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The Impala SS Frequently Asked Questions List

The frequently asked questions list serves as a central clearinghouse of information that the mailing list has gathered about the Impala. The FAQ is an active thing: as we learn more, the FAQ grows. Thanks to all of the contributors to the list! For daily and more up-to-date information, join the Impala SS mailing list or try the AskDoom technical mailing list.

Master Index

-- Engine --

Aftermarket Air Intakes

Q: Any aftermarket air-intake upgrades available?

A: Arizona Speed and Marine makes a nice system:

The K&N cone filter ends up underneath the splash guard inside the left fender. This is where the cold air comes from. Note that you have to drill a 3.5" hole in your inner fender to get the bracket through. The PCM is relocated to a new mounting area on the fenderwell. There are some clearance problems with the K&N hitting the fenderwell splash guard: you either have to drill into the fender slightly closer to the front of the car than the template suggests, or just mash the K&N so that it will fit correctly. Before and after runs showed a .22 second gain in the 1/4.

Evergreen Performance recently released a kit that is very similar to the AS&M kit. The main differences are that it is a ceramic coated steel instead of chrome, so the air charge supposedly stays somewhat cooler. Also, the air filter is angled so that the fit problems that occur with the AS&M and Callaway kits are remedied. As an added bonus, it is only about $250 for NAISSO members ($300 to noinmembers), which is at least $50 cheaper than either of the other two kits.

There is also a system available from Callaway, known as the "Honker". It is a cold air system. You remove the old filter box and all resonators, reposition the computer up and aft on the fender, and drill a 3 5/8" hole straight down where the computer was. There's a big cavity below this hole that is covered on the bottom with a large (stock) hunk of plastic. The fit problem is that the hole and tube that passed through it ends up being too far aft to allow the filter to fit comfortably with the lower plastic piece that bolts up from the bottom. It can be forced, though. The unit is $295 (P/N: C9701) direct from Callaway Cars (Phone (203)-434-9002, located at 3 High Street, Old Lyme, CT 06371).

Illusions Motorsports has recently announced their cowl induction hood for the Impala. It offers true cold air induction from the high-pressure cowl area. The intake itself is polished stainless steel with a custom built airbox and K&N filter. The hood is a one-piece fiberglass unit with a decent sized scoop on it. The hood goes for $600, while the induction kit is $400. The order line is 1-800-775-2811 and the tech line is (713) 370-6062.

Several other companies are now getting into the fray, such as Hennessey, that just replace the rectangular baffle at the front of the engine and put a conical K&N on the end of the MAF. Normally, for the money, you get a better constructed unit. Higher priced units are metal where the cheaper ones are plastic. No real performance differences between them, unless you get one that draws in cool air (via a scoop or filter relocation) instead of underhood air.

Random Technology has also recently introduced a "ram air" system that mounts in the air dam below the radiator. The lower part of the system (spoiler, ram air box, duct work to air filter box) is pretty nice. Everything goes together well. The filter box bolts right to the cooling fan supports using already existing holes. The air filter box looks a little cheap (not the nice ABS plastic the factory unit is constructed of) and the duct work to the throttle body is squeezed into an oval shape and clamped to the throttle body with the factory clamp. There are several points where the plastic duct is stretched, making a potential location for a future tear as things age. A piece of bent stainless (or aluminum) pipe would replace most of the duct hose and mate to a WS6 T/A duct to the throttle body nicely, though. You MUST use the K&N filter with the filter box they use. The factory filter will not work.

ESP Motorsports, a longtime friend of NAISSO and the Impala in general, has a nice system. Instead of the traditional Camaro 1LE elbow or plugged Impala elbow, ESP takes a unique approach. They supply a Corvette Throttle Body Adapter, which does not turn as the elbow does; it goes straight forward and adapts the oval throttle body opening to a circular 3-1/2" opening. This piece eliminates the "Home Plate" baffle. It includes a MAT sensor and has an opening for the distributor vacuum hose. Next comes a mandrel bent 3-1/2" aluminum air plenum. This part connects to the throtle body adapter then makes a smooth 90 degree turn toward the MAF sensor. It has a wrinkle finsh black powder coating and looks like it came from the factory. This piece eliminates the 1st base/pitcher's mound baffle. At the far end of this is a stainless steel and rubber coupler for attaching the plenum tube to the MAF sensor. On the other side of the MAF, a 9" K&N cone filter is attached, replacing the factory air box, and a small clamp on K&N filter for the AIR pump. This piece does not poke through the LH fender; it sits where the factory air box was. Also worthy to note is the folks at ESP are wonderful to deal with.

The folks at SLP have also come up with a nice system. It is basically like the others, but stands out since it has two tiny K&N filters on the end instead of one large one.

The members of the Impala list have devised several inexpensive and very effective modifications to the stock intake system that are documented in the technical archives. For a maximum of $50 (or as little as $10), you can make an air intake system that flow as well as any aftermarket system that does not pull in cold air. This method has been dyno tested to provide about 10 real-world, not advertisement-generated, horsepower.

Note that GM manufactures as mass-air extension cable that you can use with custom air intakes. Part Number for Pontiac WS6 MAF extension is GM# 12529241, cost is $26.00

Several people have asked about the effectiveness of removing the honeycomb screen from before the MAF sensor. This screen is there to straighten airflow over the MAF so that it will provide consistent, truer readings. Removing it may result in a bit of a performance increase due to A) the lower restriction in the intake tract or B) the different reading that the MAF is getting helps to correct an already existing A/F ratio problem. Taking it out may cause a rough or erratic idle, and if the MAF sensor is accidentally damaged, it is an expensive part to replace. Also, you may have problems with emissions as the calibration for the stock MAF arrangement would be invalidated. It would probably be a more significant increase on a supercharged car that needs all of the airflow it can get.

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Air Foils

Q: Will an aftermarket "air foil" increase performance?

A: Maybe, but not nearly as much as they advertise. At their absolute best, expect to see about 5HP gain, but possibly none. It's one of the "it can't hurt" mods: it may get you that extra .05 that you're looking for. There are really no ill effects, other than the $50 that you'll be losing from your wallet. It's purpose is to smooth and direct the air into the throttle body, which presents a flat face to the incoming air. The airfoil splits and directs it to the twin butterflys on the throttle body.

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Serpentine Belt Squealing

Q: During the 1-2 shift, there's a nasty squeal that comes from the engine, particularly during hard acceleration. I think it's the belt. What can I do about it?

A: This is a fairly common problem with LT1's making a lot of HP (or even some stock LT1s). Remove the old belt by using a box end wrench to loosen the idler pulley: it is either 1/2" (my car, from experience) or 9/16" (from the Helms manual). You don't actually loosen anything, the pulley is spring loaded and will take tension off of the belt. Then clean each of the pulleys using alcohol or brake parts cleaner. Make sure you don't use something that will leave a residue. Cotton swabs or a toothbrush work well for getting in the grooves on the pulleys. Next, you might want to use some fine grit sandpaper across the pulleys perpendicular to their rotation to rough up the surface just a little bit. Reclean with the brake parts cleaner to remove any sanding gunk. Next, install a brand new belt, routing it in the same manner as the one you took off. A couple shots of belt dressing will finish the job. When cleaning, make sure you do the power steering pump well: that seems to be where the slippage takes place.

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Camshaft Comparisons

Q: I've heard that the camshaft on the Impala was toned down. Is that true?

A: Here's the specs:

                                 Valve Lift  Valve Lift  Valve Lift
                     Lobe Lift   1.5 Rocker  1.6 Rocker  1.7 Rocker
Application          Int.  Exh.  Int.  Exh.  Int.  Exh.  Int.  Exh.
'94-'95 B/D-car LT1 0.279 0.287 0.418 0.430 0.446 0.459 0.474 0.487
  '96   B/D-car LT1 0.276 0.285 0.414 0.428 0.442 0.457 0.469 0.485
'92-'93 F/Y-car LT1 0.300 0.300 0.450 0.450 0.480 0.480 0.510 0.510
'94-'95 F/Y-car LT1 0.300 0.307 0.450 0.460 0.480 0.491 0.510 0.521
  '96   F/Y-car LT1 0.298 0.306 0.447 0.459 0.477 0.490 0.507 0.520
  '96   Y-car LT4   0.298 0.299 0.446 0.449 0.476 0.479 0.506 0.509
GMSPO   ZZ3 HO Cam  0.316 0.340 0.474 0.510 0.506 0.544 0.537 0.578
GMSPO   LT4 HO Cam  0.328 0.328 0.492 0.492 0.525 0.525 0.558 0.558

                     B    F/Y               LT4  TPIS
              Cam   LT1   LT1   LT4   ZZ3   HOT   ZZ9
      Intake Lift  .418  .447  .476  .474  .525  .484
         Duration   ---   205   203   208   218   212
  lobe Centerline   ---   117   115   109   ---   ---
     Exhaust Lift  .430  .459  .480  .510  .525  .520
         Duration   ---   207   210   221   228   226
  Lobe Centerline   ---   117   115   115   ---   ---
  Lobe Separation   ---   117   115   112   ---   112

All durations are reported at .050 lift. The LT1 cam duration specs are from an article in '92 and at that time the lift was .450 for both intake and exhaust. I don't know if the duration specs have changed since then, but I don't think they have. Note that the LT1, ZZ3 and TPIS ZZ9 cams are with 1.5 rockers, with the LT4's 1.6 rockers the lift works out to the following:

                LT1  LT1  LT4  ZZ3  ZZ3  HOT  ZZ9  ZZ9
Cam/Rocker      1.5  1.6  1.6  1.5  1.6  1.6  1.5  1.6
 Intake Lift   .450 .480 .476 .474 .506 .525 .484 .516
Exhaust Lift   .460 .490 .480 .510 .544 .525 .420 .555

The ZZ3 cam is from a smog-legal crate motor that Chevy sells as an upgrade in the '85-'87 F-cars. It is a street cams that will produce good vacuum and run with a stock converter. Installation in a Corvette LT1 resulted in a 30 HP peak gain, with more HP and Torque everywhere in the rpm range! The cam (P/N 10185071, cost $173.58) could be worth even more power compared to the cam used in the B-cars.

There are two versions of LT1 with respect to the camshaft, water pump, and distributor drive system. These parts are not interchangeable between the 1st and 2nd designs. The 2nd design camshaft features a slightly modified drive end with a larger pilot hole and a longer pin for the drive mechanism. The 2nd design water pump is modified for the new drive, and the 2nd design distributor has a modified drive and a moisture ventilation system that taps into the air intake duct. The ventilation system was added because the low mounted distributor tended to pick up moisture, causing it to misfire. '94 and up B-cars have the second design, and all other LT1's got it in '95.

The ZZ3 cam uses the 1st design, which is the same cam as on most Chevy smallblocks. Fortunately the pilot hole can easily be machined to the larger size and a longer pin installed by any competent machine shop in about 15 minutes. This modification would have to be done to the cam to be used in a 2nd design application, or you could change the water pump and distributor back to the 1st design type (not recommended!).

Myron Cottrell, President of Tuned Port Injection Specialties (TPIS) suggests the ZZ-9 cam with the 700-132 springs. He indicated that this combination would work well with the stock iron heads and would not require any machining, and that this cam on a stock aluminum headed LT1 produces 60 plus horsepower. He estimates at least 40 horsepower on the iron headed impala. The cam is $375 and the springs are $126. He also indicated that these springs would work with 1.6 roller rockers. He has found better HP numbers by staggering 1.6 roller rockers on the intake and 1.5 rollers on the exhaust. The duration of the ZZ-9 is 211 intake and 226 exhaust at .050. The lift is .485 intake and .525 exhaust with lobe separation being 112 degrees.

Another interesting way to compare camshafts is to compare the engines corrected compression ratio:

Graphic solution

  1. Draw a long vertical line to represent a cylinder bore axis.
  2. Draw a circle at the bottom with a diameter equal to the stroke.
  3. Mark TDC and BDC one con-rod length from the circle top & bottom.
  4. Mark the angle on the crank circle where the intake closes ABDC.
  5. Draw in the con-rod from this point to the cylinder axis.
  6. That new point to TDC is the effective stroke.

The effective stroke can be use to calculate the effective compression ratio which is an indicator of low rpm torque.

After you draw this picture you can work out the equation for it. Assuming the intake closes between 0 and 90 degrees ABDC:

Effective Compression Ratio = CRe
Combustion chamber volume = V
Effective stroke = Se
Cylinder bore = B
Crankshaft Stroke = Sc
Valve Closing Angle ABDC = A
Rod Length = R

Se = R + Sc/2 - (R^2-(sin(A)Sc/2)^2)^.5 + cos(A)Sc/2

Should compare to the graphic answer above.

CRe = ((Se * Pi(B)^2/4) + V)/V

This is (Effective stroke X bore area + Combustion chamber volume) / Combustion chamber volume

As you may know, any aftermarket cam needs to have a dowel installed in it for the distributor on the LT1. Here is the information you will need to have the machine shop take care of that:

                 -       -
   -------------/     -   |
  /                   |A  |B 
  \                   |   |
   -------------\     -   |
                 -       -

The approximate dimensions are as follows:

A = 12mm
B = 17mm
C = 3mm
D = 26mm

The hole just has to be large and deep enough to clear the distributor pilot shaft. Converting the metric measurements to english basically says we have about a 1/2" diameter hole (A) that is about 1" deep (D). There is a chamfer on the entrance to the hole about 1/8" deep (C) that extends it to about 11/16" in diameter (B). I'm not sure if the chamfer is important at all, but that's what it is on a stock cam.

There is already an existing pilot hole in the older design cams like the ZZ3, but it is not as large in diameter nor as deep. Any machine shop should be able to enlarge (drill out) this hole easily.

The newer design LT1/LT4 cams also use a longer dowel pin in a hole to the side of the pilot hole. The new dowel pin is the same diameter as the older one, it is just longer. The new pin protrudes 14mm or about 9/16" out from the end of the cam. This new design pin is available from GM under part number 10214485 (cost $0.92). It is a simple matter to pull out the existing (shorter) pin and tap in the longer one.

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Performance PCM Programs

Q: Are there any "chips" that I can swap in for better performance?

A: There have been several factory updates. Unfortunately, it appears that the first may have a desirable "second gear start" function that the second and third seem to lose.

Calibration History for the '94 Cars

Calibration History for the '95 Cars

Calibration History for the '96 Cars

To get the latest stock calibration, you should compain of a chuggle or a surge between 40-65MPH and during a low angle uphill and downhill grade. It could also set an intermittent DTC 32 (EGR valve malfunction). The dealer should reflash the EEPROM for you as per TSB 57-65-17.

The Impala (and all LT1 equipped cars) no longer have removable EPROMs that are simply swapped out. Instead, the PCM contains an EEPROM that can be reprogramed from the diagnostic port. If you want to replace your PCM or get a spare when you send it away to be reprogrammed, there are only certain LT1 PCM's that will work. The 94-95 Vette PCM is different than the Impala/Z28 PCM. The number to get for the 94-95 Impala is P/N 16188051. This is used only on the LT1 and the L99, so it can be out of any 94-95 Caprice, Impala, Roadmaster, Fleetwood, Trans-Am, Formula, Z28, or B4C Camaro. For 1996, all L99, LT1, and LT4 engines use the same PCM. This is P/N 16214399.

There are several devices that allow modification of the stock PCM program:


The HyperTech is a true PCM reprogrammer that will download the stock PCM program into itself, modify it, and rewrite the flash ROM in the PCM with the modified program. It also keeps a copy of your stock PCM program so you can return the vehicle to completely stock setup in minutes. Supposedly, the Power Programmer Plus is due to be released soon, which allows user modification of all of the parameters under PCM control (shift firmness, shift points, fan temps, gear changes, etc.), as well as allowing different chips to be plugged into it. You will no longer need to buy a programmer: you can use someone elses and just buy a chip. Also, this tool will have the capability of being used as a scan tool, much like the GM Tech 1 scanner.

Program Features

For everyone out there with a Hypertech Power Programmer that do not like the higher shift points programmed in but like the other changes, there is a way to use the programmer and retain the stock shift points at the same time if you have the stock 3.08 gears in the car. When you start the reprogramming process, the unit asks if you would like to see more options. Choose yes, it will then ask you if you have ZR or VR rated tires. Choose yes, of course (unless you do not). It will then ask if you have certain gear ratios. Say no to ALL ratios you are asked about, even the one that you have. The Programmer will then reprogram the car but leave in the stock shift points.

The new Hypertech Power Programmer Plus is now just coming into production. It corrects for virtually any gear ratio available up to 4.10, tire diameters from 24"-30" for speedo corrections, shift firmness at all throttle positions, fan temperatures, and adjustable WOT shift points. The PPP comes with a very detailed manual for ease of use and takes about 7 1/2 minutes to load. The engine tuning is similar to the original Power Programmer. Members have reported a .3 second gain in the 1/4 with the new programmer over the old one. However, several users have reported problems with Hypertechs calibration for different rear gears.


SuperChips will reprogram your PCM for you in much the same way GM does. However, you must ship the PCM to them (causing downtime for your car) or drive to one of their authorized reprogramming facilities. SuperChips will also dyno-tune your car to make the most power with your current mods. Recently, SuperChips has performed dyno testing on all of the current chips out there, and have constructed a new chip which has greater power gains than any of them. This chip will be sold for about

Program Features


Jones Electronic Technologies (JET)

The JET device does not really modify the PCM program in the car. Instead, it works by intercepting the sensor signals and modifying it so the PCM outputs will be modified. JET industries claims that this was necessary to get outside the "walls" created by the stock PCM.

Program Features


"Z" Industries

The "Z" Industries chip Program Features



F-body Calibration

A possible option for those who have made the 3.42 rear gear swap is using the F-Body (Camaro/Firebird) calibration for the 3.23 gears and automatic transmission. Program Features



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Valvetrain Clatter and Ticking

Q: There's a lot of ticking/clattering coming from the valvetrain. Is this normal?

A: For the Impala, it is normal. The increased noise is due to the metal valvecovers used instead of the thick plastic ones on the Corvette. The LT1 is bad in this respect.

A TSB has been issued that covers some of these noises. Contact your dealer if you are concerned. The TSB follows:

Chevrolet 67-61-14
Issued 04/18/96

Models: 1994-96 Buick Roadmaster
1994-96 Cadillac Fleetwood
1994-96 Chevrolet Caprice, Impala SS
With 4.3Lm 5.7L V8 Engine (Vins w, p - RPOS L99, LT1)

Subject: Engine Noise (Install Valve Stem Oil Seal)

Condition: A rhythmic engine noise at idle. The noise, which occurs at half engine speed, has been described as a "whoop whoop" (similar to a helicopter idling), and engine rattle noise (not to be confused with pvc rattle), a lifter tick in the lower end, a balance shaft noise, or a rod knock. When using a stethoscope, the noise will sound as coming from deep within the engine. The noise may be heard in the passenger compartment and in s/t vehicles is audible at the catalytic converter and tail pipe.

Important: The noise will get louder as the engine warms up at idle. The noise does not diminish with removal of the accessory drive belt, balance shaft gear, or disconnecting the torque converter.

Cause: The noise may be caused by a low level of lubrication on the exhaust valve stem, creating a "slip-stick" condition between the valve stem and the vlave guide.

Correction: Install the valve stem oil seal listed below, on the exhaust valve guides only. Lightly lubricate the seal, and with finger pressure only, push it on to the valve stem and down on to the exhaust valve guide. Important: Do not install this seal on the intake valve guides. The seal is not released for intake vlave application in the above indentified vehicles.

New rocker cover gaskets may be required.

Parts are available from GMSPO as follows: LT1 oil seal, 8, P/N 460483

Iron Head Rocker cover, 2, P/N 10046089

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Unconnected Connectors

Q: I found a connector with no mate on my car today. Did something fall off, or was never installed from the factory?

A: Probably not. The wiring harness for the engine is the same for the Chevy's, Buick's, and Caddy's, so there are some unused connectors that are simply hanging there in the Chevy. The most famous is a little blue connector near the hood latch brace. This is for the outside temperature sensor for the Buick's automatic climate control.

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Differences Between LT1 Engines

Q: What are the major differences btween the LT1 in the Camaro and the Impala LT1? How about the LT4?

Major Differences Between the F/Y-Car and B-Car LT1 Engines
Item/Description F/Y-Car B-car
Block mains: 4-bolt (Y-Car) 2-bolt
Heads: Aluminum Cast-iron
Cam lift specs: .450/.460 (int/exh) .417/.429 (int/exh)
Valve springs: 268 lb/in 393 lb/in
Valve spring od. 1.300" 1.241"
Valve spring inst ht: 1.78" 1.70"
MAF id: 3.5" 3.25"

In the F-body applications, the alloy heads have larger intake ports giving lower port velocities meaning they have a tendency to produce lower torque at the bottom end. They also have different exhaust ports ("D" shaped) which flow better, producing more power throughout the range. Aluminum conducts heat much better which reduces the tendency to get for ping-inducing hot spots, allowing higher compression. The iron heads are much more resistant to warping from heat, though, and the valve size and design are optimized for torque. Several engine builders have found that porting stock iron heads on an Impala produces better results than bolting on the aluminum heads.

As for differences between the LT4 and the LT1:

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Diagnosing Electrical Problems

Q: My Impala has intermittent electrical problems (flickering instruments or lights, engine hesitation or stalling), or the cover to the auxiliary battery connection has melted (near the underhood electrical center). What's up?

A: Under certain conditions, the battery cable connection at the underhood electrical center stud may overheat. This may cause melting of the plastic batter cable cover, the plastic stud housing, or the stud itself, resulting in intermittent loss of vehicle power. This is more likely to occur if extra electrical loads are added to the car. The fix involves moving the terminal, and is coverd in TSB 43-81-48.

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Engine Dress

Q: What can I do improve the looks of the engine compartment or at least open up the stock air intake path up a little?

A: There are several area to address:

As for the stock air box, several list members have cut additional holes in it underneath the air filter. This, along with a K&N filter, allows the engine to breath a lot better than the small, stock, inlet does. You might also want to consider one of the aftermarket intakes available for more flow improvements. Another option is to connect a conical K&N filter to the end of the MAF and leave the top of the airbox off for a replacable, free-breathing system. See the air box modification instructions in the technical area for details on doing this.

The square baffle between the MAF should be removed. It just limits full throttle noise, and for most of us, this isn't a concern. It also introduces turbulance in the intake stream, which robs power, and is a concern for us. The simplest solution is to replace it with a straight piece of pipe (PVC, chromed, or stainless), or you could also route a 3" hose right through the square baffle to preserve the "stock" look and get the same benefits. The aftermarket intakes usually eliminate this baffle as well as the stock air box. Check the section on removing the rectangular baffle in the technical archives for details on this operation.

The intake elbow and the "home plate" baffle on top of the engine are interrelated. Unlike other LT1 intakes, the Impala elbow has a hole in the top of it that connects to this plate. If you are removing the top baffle, you must either plug this hole or replace the elbow. You can plug the hole by inserting something (a paint can top w/ duct tape, a plumbing test plug, a Nestea cap, a hockey puck, a water heater tee cap, and others have been suggested and used) into the hole on the bottom of the baffle. The duct in the top of the elbow is then closed off. You can also replace the stock elbow with one from a 94-96 1LE f-car. This is documented in the home plate removal section of the technical archives.

As for flow, the stock paper element flows around 200CFM, the K&N replacement for the stock element flows around 410CFM, and the conical filter replacement will flow up to 900 CFM. At peak volumetric efficiency of the intake, the LT1 will ingest around 530CFM at 5500RPM. This can be calculated using the formula cfm = (cid * rpm * Ve)/(3,456).

Here, Ve = volumetric efficiency. That is basically how well your car sucks. CC said a typical street car has a Ve of around 0.85, whereas a racer can be 1.0 or higher (how higher, I don't know). If we figure 0.85 for the Impala, this revises the peak figure down to 473 cfm at redline.

As for other mods, you can install the Corvette fuel injector covers and plastic valve covers. This totally changes the apearance of the engine and makes it look like a Corvette LT1. You can also add red Chevrolet "SS" emblems on the fuel injector covers which come originally on the doors of '95 Chevy S-10 "SS" model pickups. These emblems could also be used on the elbow caps, as referenced above. Check out the Corvette engine dress section of the technical archives for more information.

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Lowering Cooling Fan Turn-On Temperature

Q: Can I keep my engine cooler by modifying the fans?

A: You could install an aftermarket PCM program that changes the temperature where they are supposed to come on. This will be in effect all of the time. JET also makes a kit that will turn the fans on at a cooler temperature: it wires into the stock harness.

Alternatively, you could install a factory thermostatic switch in a pre-existing (plugged) water jacket hole in the LH cylinder head, and then wire it through a hidden toggle switch (mounted in the under-hood relay box) to allow you to turn on the high and low speed fan relays automatically at 203 degrees or manually. The thermostatic switch is wired in parallel with the standard fan relay circuit so the PCM can still control the fans as normal. BTW, the thermostatic switch is the same one installed in the intake manifold as the high speed fan switch in the GN and TTA.

There are two sources for the thermostatic switch. There is the factory GM unit, and a company called GMP Parts Co. (916-685-1055) manufactures an improved version. If you want the improved design switch, call GMP, ask for John Flagg and tell him Scott Mueller sent you. The GM switch is available under P/N 3053190 and costs around $20. This switch has a 3/8 pipe thread, and there are 3/8 pipe plugged holes in the LT1 cylinder heads that are just perfect for installing this switch.

As for other modifications to help your LT1 "keep its cool", replace the factory thermostat with a 160 degree unit. These are available from many of the LT1 aftermarket vendors. Removing home plate also allow the engine to cool off faster, and allows you to lay bags of ice on the intake for engine cooling at the drag strip.

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Adjustable Fuel Pressure Regulators

Q: Will an adjustable fuel pressure regulator help my car?

A: The PCM controls the air / fuel ration using the O2 sensor at just about all RPMs except WOT. Any increases in the fuel pressure at this point will just result in shorter pulse widths and probably worse performance. At WOT, an adjustable regulator may buy some extra power if you have done other modifications to the engine, such as an aftermarket air intake and an aftermarket exhaust system . I don't think anyone on the list currently runs with an adjustable regulator. An adjustable regulator could also be useful at the track to tune for environmental conditions or altitude. However, several magazine reviews have found that there is a very narrow window (+/- .5 PSI) where the LT1 begins to lose power rapidly, and they only gained a couple of HP in the best cases.

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LT1 Head Comparison

Q: How do the heads compare between the Impala SS LT1, F-Body LT1, Corvette LT1, and the Corvette LT4? A: The Corvette and F-Body LT1 heads are identical aluminum units, while the Impala version is iron. The LT4 heads are completely different. Here's how they compare on several critical areas:

Also note that there are three gasket types available: iron head LT1, aluminum head LT1, and aluminum head LT4. The aluminum head gaskets are thicker than the other two to pass GM's extreme thermal testing with the aluminum head, giving up about 1/2 a point of compression over the iron head gasket. Some investigation may be necessary to determine if the iron head gasket will rust the aluminum heads, though. The LT4 piece, while still giving up 1/2 point of compression, is a top-of-the-line, bullet proof unit. This gasket is recommended if you are running a blower or nitrous.

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Police Package Silicone Hoses

Q: What's the deal with the green hoses on the Police Package Caprices?

A: This is option 1T1: "Hose, Radiator and Heater, Silicone Rubber (SEO)". These are green silicone radiator and heater hoses that directly replace the factory hoses. They replace all of the black rubber hoses between the radiator, engine, heater core, overflow tank, and thermostat housing. These hoses are made from 100% pure silicone rubber and will last the entire life of the vehicle, they never need to be replaced. They are installed with 100% stainless steel (including the screw) worm gear clamps (as used in the factory Police package) instead of the standard squeeze clamps for additional durability and reliability.

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Knock Sensor Readings

Q: I used a engine monitoring tool (e.g. Diacom, Auto-Xray, or Tech 1) on my engine and see retard as I floor it, no matter what octane I use. Is there something wrong with my engine?

A: Probably not: it could be because of emissions. Many cars retard the timing on take-off (slightly retard and *then* advance) to reduce the emissions. If you have a scan tool that can handle it, check the parameter "KNOCK SENSOR" in the PCM. It's a numeric counter that records the number of knocks that the knock sensor has detected. If you have the capability of data capture on your tool, do a run and look at the KNOCK SENSOR parameter over the time course of a perceived knock condition. That should tell you if the retard is actually due to "real knocks" or some other reason. If it increased, your knocking. If not, you have something else going on. BTW, the parameter "KNOCK RETARD" will tell you how many degrees off of the optimum timing the PCM has retarded your timing to counteract a detected knock condition.

If you know that your knock sensor is firing off without the engine knocking, then you can "desensitize" it electronically. NAISSO member Steve Chapple ("Rocket") came up with the following scheme.

I measured the knock sensor circuit (2 sensors wired in parallel to ground, see diagram below) at the dark blue wire at the PCM to be around 1925 ohms. This is consistent with Mike Chaney's measurement of 3850 ohms for the F-body's one sensor. 3850 in parallel with 3850 is 1925 ohms (R1*R2/R1+R2). Our Impala most likely uses the same knock sensor, we have two vs. one on the F-body.

Original Circuit:

               ____________       dk blue wire               |       |
--|||---------|knock sensor|---|-----------------------------| PCM   |
ground         ------------    |                        D22  |       |
               ____________    |                       blue  ---------
--|||---------|knock sensor|---|                       connector
ground         ------------
To desensitize the sensor circuit you can add a resistor network between the PCM and the knock sensors (see circuit below). You simply cut the dark blue wire (D22) in the "blue" connector bundle a few inches from the PCM and place the following circuit in line. R1 goes to ground (screw on the PCM) and R2 goes in series before the PCM.

Desensitized Circuit:

    dark blue wire       cut                             cut          |      |
  <---------------------/ / /---|----------/\/\/\/------/ / / --------|  PCM |
   to knock sensors             |             R2                  D22 |      |
                                |                                     |      |
                                |                                dark +------+
                                >                                blue wire
                                < R1
                                -   Ground
Ah...the resistor values, yes we need that. I calculated values for a 25% reduction and 33% reduction. I have the formulas below if you want something more or less.

33% reduction: R1 = 3856 ohms, R2 = 641 ohms
25% reduction: R1 = 5779 ohms, R2 = 481 ohms


R3 = (1-X) * Rk, where X is the desired reduction (i.e. X= .25 for 25% or .33 for 33%)
Rk = 1925 ohms which is the measured resistance of the knock sensors at the blue wire
R2 = Rk-R3

After a little algebra:

R1 = Rk*R3/Rk-R3

You may not be able to find the exact resistor values. You can build them by adding smaller resistors together.

In the DC (no knock) state, the PCM still sees the 1925 ohms resistance. Under a knock condition, the knock sensor will send a voltage to the PCM which will be attenuated by the series resistor R2. R1 really has no attenuating effect.

This idea worked for Mike Chaney's '95 Trans AM. He had a stumble at around 5000 RPM that he thought was being caused by false knock. His 25% reduction circuit cured the problem.

Note that the circuit as shown will only apply to the 94 - 95 cars. They use the 10456126 knock sensor, which has a 4K ohm internal resistor. The 96 switched to the 10456017 knock sensor, which has a 100K ohm internal resistor. The circuit would have to be revamped accordingly to compensate for the difference in sensors on the 96.

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LT4 Engine Swaps

Q: What would it take to swap an LT4 into an Impala?

A: Not much! Some members have already even done this. The LT4 crate engine options can be summarized as follows:

LT4 '96 Corvette Production Engine - p/n 12551183, $5,950 list, $4,462.50 dealer cost. This is a complete '96 Corvette engine which includes everything from the oil pan to intake manifold with throttle body, fuel rail, fuel injectors, opti-spark distributor, ignition module and coil, spark plugs, and even wires. It also includes 'vette exhaust manifolds, water pump, harmonic balancer, accessory bracket, all engine sensors such as knock sensors, temperature sensors, oil psi and temperature sensors, and the throttle position sensor. It even includes $1,800 worth of (unnecessary) 'vette flywheel, magnesium bellhousing and clutch.

When installing this engine in an Impala, you will be removing the following parts and replacing them with the equivalent parts from the LT1 in the Impala or discarding them completely.

These are all NEW parts that come on the production LT4, and will be left over after the swap is complete. The magnesium bellhousing and clutch alone sell for $1,800 new, the injectors are over $600, throttle body is $450, exhaust manifolds are $275, and the water pump is $70. These items, along with the original LT1 from your Impala, can really help to subsidize the installation.

You also get many other notable items with the production engine including a new $450 distributor, $200 worth of red LT4 sparkplug wires, a $25 '96 higher energy ignition coil, new updated double platinum '96 sparkplugs, various new engine sensors, and even 6 qts of Mobil-1 oil and a PF-52 filter already installed.

Unfortunately the complete production engine will not be available much longer. There were only 300 extra LT4 engines left over after the '96 production run, and SLP took over 100 of them for the 100 '97 Camaro SSes they will be building with LT4 engines. The rest are the only ones left over for warranty and service exchange as well as over the counter sales.

To fill the gap once this engine is gone, GM Performance Parts has introduced a new LT4 Engine Kit, p/n 12371172. This is a 3/4 LT4 engine which is commonly referred to as a long block. This engine includes everything up to the heads, but is not a fully dressed production engine. It does not come with an intake manifold, fuel rail, injectors, throttle body, engine sensors, wiring, spark plugs, distributor, or exhaust manifolds. It does include a separate kit of parts with a 4bbl carbureted intake manifold, HEI distributor, Corvette water pump and harmonic balancer. Unfortunately all of these extra parts except the balancer are not needed in an LT1 swap situation and they will be left over. These parts are also not installed on the engine and do not include attaching hardware or gaskets.

You will need to purchase an LT4 intake manifold to complete the kit. The following parts will be left over from the LT4 Engine (3/4 engine) Kit:

Most everything else that is needed would be swapped over from the LT1 engine including the following items:

Note that the LT4 Engine Kit is ideal for an LT1 swap since most of the missing parts you would need come off of the existing LT1 anyway. The only difference between using the Production LT4 vs. the LT4 Engine Kit is that you will have many more parts left over to sell if you start with the production engine compared to the engine kit version.

Theoretically the LT4 Engine Kit should be much more economical than the production engine due to less leftover parts, however if you can sell those leftover parts, it may shift the economy over to the production engine. I calculate roughly $3,200 worth of NEW parts will be leftover after the swap using the production engine, assuming you can get half price for them, that would mean a $1,600 rebate on the deal. Not to mention if you sell your original engine for $2,000 then the total cost of the LT4 swap is now only about $1,000 using the production engine!

As a side note, the paint code for the red LT4 intake color is GM70. The "universal code" WA-9075 is non-vendor specific and any shop supposedly can mix a WA paint code, so you may want to try that. Any GM shop should be able to get you the GM70. You may need to add a clear coat on top to get the correct effect.

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Mobil 1 Oil Cap and Plate

Q: Will the Corvette "Mobil 1 Only" oil cap and plate fit on my Impala?

A: If you have a '94 or if you have switched to the Corvette valve covers, you can use the Corvette oil fill cap (P/N 12554955). Normal '95 and '96 cars can not use the cap due to a different oil fill neck. The plate/sticker can always be used, but the "best" mounting spot is where the first intake resonator rests on the radiator shroud, but other more creative mounting spots are also possible.

To construct a cap for the 95-96 models, or if you just want to use the new multi-colored cap from the C5 'Vettes, check out the technical archive on how to create one.

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Nitrous Oxide

Q: Is there a nitrous oxide system available for the Impala?

Compucar makes a "wet" system for the LT1 which fogs fuel and nitrous through a plate that mounts in between the TB and the intake. From what I can gather, Compucar is a great company to deal with and they warranty every part of the system for life... no questions asked. The "supposed" weakness of this system is that the fuel may not make it back to the rear cylinders due the inadequacy of the fogging system and the design of the intake being optimized to flow air and not fuel. This bit of info comes mainly from the NOS guys trying to sell you their "dry" system (see below). The Compucar system is a 75/150HP system and can be purchased for around $600.

NOS makes a "dry" system that sprays nitrous thru the throttle body elbow into the intake. To get the added fuel, they increase fuel pressure with an added in-line fuel pump and decrease the return pressure to the fuel tank. This system is supposedly a bit more complicated to "tune". There is also questions about whether the injectors will work properly/effectively at the higher rate/pressures. From talking to people who have used the NOS and the Compucar, they say that the Compucar system is much better in pure quality of parts down to the brackets that hold the bottle in. NOS supposedly is not as flexible to deal with on parts/problems. NOS has 85% mkt share and are the current leader in Nitrous systems. The obvious risk of this system is that if you have a problem with fuel delivery on one of the cylinders, you have major problems! This is a 150HP system, part # is 05176, and jobber price is $675.00. It gives you everything you need for installation except the car and the guy/gal to do the work. You can use up to the 125 HP jetting without having to modify the internals of your Impala's engine. The jetting comes soft (rich) from the factory because of temperature differences around the country. If you were using the kit in hot weather all the time the jetting would be pretty close to perfect. If you use it in a moderate to cool environment you would be able to make more power by leaning out the fuel jet.

With any nitrous system you will need to retard timing. How much depends on whether you have aftermarket chips/prgmrs that advance your timing. The most flexible way I have discovered is to have something that retards your timing a specific number of degrees once the nitrous solonoid is activated. This can be done with products from MSD, etc. This lets you keep the performance advantages of your aftermarket chip/programmer while you are not on the bottle.

The million dollar question...."Will it harm my precious beast?" That one is tough to get a straight answer on. The NOS and Compucar guys say that with the 150HP kits (max. avail. for LT1) there is basically no risk in long term damage. But then they are in the business to sell systems. I would think that putting another 50% more of an explosion into your combustion chamber will have long term effects on pistons/rods/valves, etc. It all depends on how much you are "in it". From talking to people that have nitrous, it is VERY addictive and you will use it much more than you think. If you can stay out off the nitrous except at the track (don't forget about the tires you will go through) and want to have the "warm fuzzy feeling" of knowing you have low 13 sec power for that Saleen you may see in the right place at the right time, then go for it!

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Octane Ratings

Q: What octane rating should I use in my Impala? Will I gain anything going with a higher octane?

A: Octane is added to gasoline to prevent knocking. If knock is detected in an Impala engine, the timing is automatically retarded to prevent any damage to the engine. However, retarding the timing also decreases the power that the engine puts out. Under normal circumstances, a stock Impala can run fine (i.e. no spark retard) on 87 octane gasoline. Factors such as heat, load, and gasoline quality affect the point at which the engine begins to knock. To ensure maximum performance, some owners run higher octane ratings to prevent any chance of knock.

Octane ratings have little effect on mileage, and the extra cost you pay at the pump would most assuredly negate any mileage gains you would experience from running a higher octane, anyway. Also, the same cleaners are put into each octane level, so don't believe the hype at the pump.

If you are using a performance PCM package, such as the Hypertech or SuperChips programs, then you probably need to use premium gasoline all the time. These programs are tuned for 92-93 octane to get the most power out of the engine (through advanced timing). The same thing goes for superchargers or nitrous applications.

Another data point to remember is the oxygenated gasoline (sold in some state year around and in others in the winter) contains less energy per gallon than conventional gasoline. Thus, power levels and mileage levels will be lower than with "normal" gasoline.

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Adding an Oil Cooler

Q: Is there an oil cooler on the Impala?

A: Yes, there is. It is internal to the radiator. You could also special-install option 7P8: "Cooler, High Capacity Engine Oil". This is a heavy duty external oil-to-air aluminum plate cooler, similar to the external oil-to-air trans cooler, which is mounted on the LH side of the vehicle directly in front of the radiator. This cooler is standard on all Caprice police package vehicles, and replaces the oil-to-water cooler inside the LH radiator tank on civillian LT1 Caprices. It includes all aluminum pre-bent lines from the oil filter adapter and replaces the lighter duty oil-to-water cooler located in the LH radiator tank which is standard on the SS.

You'll need the following parts (net prices):

The main installation hitch is unbraiding the oil Level & O2 sensor wire harnesses from the existing cooler lines. The oil level wires attach inside the sensor housing & are difficult to see. Use a small pen light to see the tab on connector, lift the tab with a small screwdriver, and gently pull wires out. The O2 connector is on the side of the block above oil level sensor. Squeeze the connector together to remove the light grey holding pin before pulling connector apart.

When you get your parts from the dealer, use the Cooler part # and have him screen print what the assembly looks like on the car. You should get a really nice parts explosion of all the parts and where they go.

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Spark Plug Indexing

Q: What is spark plug indexing, and what can it do for me?

A: Frank Halley writes:

Several companies sell "indexing washers" that allow you to change the orientation of the sparkplug tips relative to the head. Why you ask?

GM cut the threads for the 8 sparkplug holes in your car so they start at random angles. AC/Delco makes sparkplugs the same way. The threads on the plug are random, relative to the electrode construction. Therefore, some plug gaps point up, some down, and some sideways. However, the plugs are the most efficient when the gap faces "up" or toward the center of the combustion chamber. Otherwise the flame must travel around the electrode to get to the entire air/fuel mixture in the cylinder.

Indexing washers allow you to change how far the plugs go into the block. This allows you to change the orientation of the plug tips relative to the combustion chamber. Indexing is a good idea, but indexing washers have two drawbacks:

  1. They retract the plug tip out of the cylinder, thus making them less effective and changing their heat range
  2. They change the compression slightly (less plug in the cylinder)

There is an alternative. I bought a new set of plugs, but you could use your old plugs for this as well. Measure where the plug threads start relative to the electrode. What you want is the angle from the electrode to where the thread starts when looking at the front of the plug. Write the amount down for each plug.

Using the plug nearest 000, measure the thread orientation in all eight cylinders. I did this by putting a piece of electrical tape on my sparkplug socket that corresponded to where the gap was on the plug. Write down the values, subtracting the value of the sparkplug thread orienation each time.

Now, match each cylinder with, the plug that comes the closest to the same angle you measured (put the 45 degree plug in the 45 degree cylinder). Check the first few with the tape on the plug socket to make sure you have the angles orientated correctly relative to each other.

I ran my car with this change and the plugs gapped at 0.055" today. There were no other changes to the car. It was the same track at about the same temperature. I was able to increase my average terminal speed in the 1/4 mile from 92.47 to 93.03, and the time from 15.031 seconds w/o to 14.905 seconds with. These figures indicate about a 5HP gain.

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Spark Plug Changes

Q: What's the easy way to change spark plugs?

A: There is no easy way! Seriously, though, here are some suggestions from list members:

Spark Plug Changing Strategy
Plug Access Tools Difficulty
1 Top Socket with Short Extension Easy
2 Wheelwell Socket with 10" 3/8 Extension Very hard: remove the right front wheel, go through wheel well
3 Top Socket with Short Extension Easy
4 Wheelwell Socket with 10" 3/8 Extension Very hard: remove the right front wheel, go through wheel well
5 Top Socket with Short Extension Easy
6 Top Socket with Short or No Extension Moderate
6 Bottom Socket with Short Extension Moderate - watch out for cat and manifold
8 Top Socket with Short or No Extension Moderate

Some other tips:

  1. Be sure to re-install the heat shields on plug wires 6,7,8. If they touch the headers, they will fry.
  2. Purchase 5 more heat shields (p/n 12132232) and install them on plug wires 1,2,3,4,5. The other 5 plug wires need to be protected from the heat of the headers. The engine bay will also have a consistent look when the hood is popped.
  3. Lube both ends of each plug wire with dielectric grease, eliminates moisture and corrosion, and increases conductivity. The next tune-up, plug wire removal will be a piece of cake.
  4. Wear a long sleeve shirt and surgical gloves to cut down the scratches and cuts to the hands and arms while removing and installling the plugs.
  5. Use the '96 Impala AC 41-943 double platinum plugs (p/n 25166821) for better cold winter starts and performance. The Bosch Platinum plugs part number is HR8DPX Resistor 4205, if you want to go that route. However, a number of members have had problems with the Bosch plugs burning up rather quickly.
  6. Another useful tool to use is a T-handle spark plug tool. One mode is the THORSEN Professional 5/8" Spark Plug Tool: insulated T-type handle with swivel action socket. The part number is 158571. Thorsen Tool Co. is in Rockford, IL.
  7. Reserve about 3-4 hours, it'll take that long to complete the job.

"Been there, Done that several times"!! Back to the index...

Underdrive Pulleys

Q: Would underdrive, "power pulleys" free up some more power in the Impala?

A: In a word, no. The Impala has a 140amp alternator putting out 13.8 volts, which equates to a maximum output of 1932 watts, or 2.591 horsepower to run the alternator. So, accounting for ineffeciencies, your alternator is only pulling 3HP, at most (all accessories running). More often, it's more like 1.5HP, where a 1/3 underdrive pulley would save you only about .5HP. Actually, this is the best case for the pulleys: in fact, the alternator will put out current to match demand at RPM's above idle. This means that the only affect of the pulleys will be to reduce idle output from 75-100 amps to around 50 at idle. You would no longer be able to run all accessories at once without discharging the battery. In addition, there is more drain on the alternator once you start to run the motor because it has to recharge the drained battery.

Also, being that they are made out of soft aluminum, the belt will actually wear the pulleys over time, causing belt slippage, belt mis-alignment, inbalances, and other problems. This does not happen with the stock steel pulleys. If all you wanted was appearance, you should have the stock pulleys Jet Hot coated or perhaps powder coated or something. This would look good, and retain the proper charging at idle of the stock pulleys.

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Roller Rockers

Q: What about using higher ratio rockers for the engine instead of the cam swap?

A: Crane offers self-aligning, 1.6:1 rockers that effectively increase the lift of the stock camshaft. There are no piston to valve clearance problems with these rockers. Several members of the list have used these and have had good results. Prices have been quoted from $275 to a bit over $300 for the parts. You can expect at least a 15HP gain with this modification. They have been found to be somewhat noisy in some installations, though. You should also get the K-Motion #0700 springs to complete the package, or you will probably get into valve float.

When installing the rockers on a stock cast iron head, be sure to check pushrod clearance as the steeper rockers alter the geometry slightly, and the pushrod clearance is tight. If you also upgrade to a higher lift or duration cam, you will probably need to get the heads machined to accept guideplates and screw studs. This will also allow you to use the standard, non-guided rockers. You should also get hardened pushrods from 94-95 LT1's (the 96's are non-hardened).

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LT1 Scan Tools

Q: Are there "scan tools" available for the LT1 that allow me to monitor the various engine parameters at work?

A: There are several. The best, by far, is the GM Tech 1 scan tool, which is used by the GM dealerships. However, at over $1000 a crack, this is out of the normal "mod" budget for most of us.

The next best solution is the Diacom by Rinda Technologies. Diacom is a package that will run on most laptops and can monitor and record most PCM activity for 94-95 cars. 96 support is currently incomplete, but most values are present. For more information, see their website at The Auto-XRay is made by Jones Electronics. It is a stand-alone electronic device that can plug into the ALDL port on 94-95 Impalas. I am not sure if it works on 96s or not. Current best price is $??? from $??? (can someone help me here??? More info, please???). A NAISSO member is making a tool called the Scanmaster LT1 that is designed to display and record critical data from the PCM. The product is a small plastic box with the front panel being an LED readout. It just happens to fit in the hole that the junk tray sits in in the pull-out ashtray. It is also very easy to install since it only requires tapping into 12V+, a ground and the data wire that goes to the ALDL above your right knee.

In regular (closed loop) mode, the left side displays O2 sensor data and the right side displays the amount of spark timing retard. The fun begins when you step on the gas than one!) since the Scanmaster goes into record mode. What it records is the lowest O2 reading and the highest spark timing retard value along with both events' associated MPH (the reason for MPH rather than RPM is that the engine could see the same RPM at multiple vehicle speeds). This data is stored until the next time you step on the gas.

The extended mode is where you get to view the rest of the data:

If you want to get in touch with the mastermind behind this, Bob Bailey, you can email him at and tell him Scott Knight sent you. The place to get the Scanmaster is Modern Musclecar at 810-777-2299 and you need to talk to Mike. The price is $249.

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Speed Limiter

Q: Is there a top-speed limiter on the Impala?

A: Yes, for 154 MPH, which is really a non-issue since it is drag-limited (in stock form) to about 140, anyway. Some '95s may have gotten the incorrect speed limiter due to the wrong tires getting put on the car. The dealer should fix this. Note that this speed occurs in overdrive, not third gear. Third is "only" good for 125 or so.

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Engine Thermostat Torque Specifications

Q: The torque specs in the manual seem high for the thermostat housing. Are they correct?

A: NO!! Both the factory service manuals as well as the Hypertech documentation are INCORRECT with regards to the thermostat housing bolt torque. If you follow the incorrect specs (which are 3 times more torque than what is correct), you will either strip the threads out of the soft aluminum waterpump, or you will break the heads off of the tiny 5mm bolts! The manual states that they are supposed to take 21 ft-lbs of torque, which is far to high for the size and material of the bolts. The correct specification for torque on the thermostat housing bolts (as found in the '96 Y-car (Corvette) service manual) is 10 n/m or 89 in-lbs, which would be 7.42 ft-lbs.

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Adding a Power Steering Cooler

Q: Is there a power steering cooler available?

A: Option 7L9: "Cooler, Power Steering Fluid (SEO)". This is a metal tube cooler that crosses the front of the vehicle from side to side directly under and behind the radiator. This is standard equipment on Caprice police package vehicles and is used to prevent the power steering fluid from overheating during spirited driving sessions.

You will need a Pipe Assembly (GM P/N 26036034) and 2 "Clamp-Lo" (GM P/N 2091638). The service manual details the installation of the lines. There's also a diagram of how to route the lines from the gear box to the power steering reservoir.

For those who like to use all OEM parts on their cars, there are also two more p/n's needed: #11509363 (10 pack of bolts), and #12337917 "Nut, RR BP" (essentially a clip with a nut on one side). These two other parts are required to correctly (as OEM) fasten the pipe assembly to the bottom of the radiator crossmember. The total cost for me for ALL of the parts for this mod is about $45.00.

Also be sure to pick up an additional 32oz of GM power steering fluid to compensate for the larger capacity, and also to use as part of the bleeding process.

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Q: Are there supercharger kits available for the Impala?

A: There are several kits available, including the Vortech, the Paxton, and the ATI ProCharger. Apparently, the Vortech guys split off from Paxton when they wanted to make some changes to the design. The Vortech is their brainchild. The ATI unit includes an intercooler which allows them to produce higher boost than the Vortech or Paxton. The Vortech installation swaps in larger injectors, and a MAP sensor to run a booster fuel pump when additional fuel is required. They also report much higher gains in horsepower than the Paxton. The Vortech uses circulated engine oil rather than a separate resevoir that must be changed like the Paxton. Several F-car people have run 12s with no other mods, and tests indicate that the Vortech on an F-car LT1 is worth 113 more HP at the rear wheels. The only company that makes a Vortech kit specifically for the Impala is Specialty Vehicles International (SVI) in Colorado Springs, Colorado, (303) 329-8238 or (719) 573-0857. The rest of the kits are adaptions (some decent, some not) of the Camaro kit.

The Paxton unit includes the supercharger, three additional injectors to supply extra fuel to the engine while under boost, and the Paxta-Map boost timing manager. The Paxta-Map allows you to dial in more injector pulse width from the cockpit as a function of boost. This allows fine tuning of the amount of fuel delivered to the engine. The Paxton system also includes a method to retard the timing as the boost grows, like the Vortech.

The ATI system is relatively new, but they claim to have built racing superchargers for a long time and have had some Mustang products around. Their "hook" is the addition of an intercooler for the boost. The intercooler allows them to run much higher boost (up to 12 PSI on a mildly modified engine) without detonating. The Paxton and the Vortech used to be available in 8 or 6 PSI units, but the 8 PSI units are no longer available, supposedly due to engine problems. ATI claims their 9 PSI unit will work fine on a stock engine. Remember that these PSI figures are probably quoted at the output of the supercharger and not at the input to the engine: the intercooler costs a few PSI. There seems to be a difficulty in getting ProChargers tuned and running correctly on the Impalas. Also, there are no Impala- specific kits available yet.

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Throttle Body Coolant Cutoff

Q: What's a throttle body heater, and why would I want to get rid of it? A: Engine coolant flow is provided to the throttle body to improve cold driveability. Engine coolant is routed from the rear of both cylinder heads to the throttle body and then to the coolant recovery reservoir."

If you determine that your car won't be driven in temperatures that would cause ice to form on the throttle body, you might consider disconnecting the heater. The heater's only function is to reduce the chance of ice forming on the throttle body. Without the heater, the intake air is cooler and the engine can make more HP.

To disconnect the heater, you will route the coolant line directly from the cylinder head to the coolant reservoir without going through the throttle body.

First, put something under the engine to catch any coolant that leaks out when reconnecting the hose. An oil change pan works very well for this. Get a rag to protect the opti-spark distributor from getting wet. Put it somewhere where you can reach it quickly.

There is a metal pipe running the length of the cylinder head on the passenger's side of the engine. It is attached to the bottom of the valve cover on the outside of the engine. There is a very short, 90 degree rubber elbow from the end of that pipe to a pipe on the throttle body. Two spring clamps hold the rubber elbow to the respective pipes. This hose is the most difficult to remove because of the spring clips.

On the driver's side of the throttle body, there is a rubber tube running from the throttle body to the coolant reservoir. It is held on with a screw-type hose clamp. This hose is very easy to remove.

You should loosen the hose from the driver's side of the throttle body first, but not remove it. If you remove it, coolant will leak out while you remove the other hose. With a screwdriver, loosen the clamp on the long hose. Get that spare rag and hold it under the hose while you momentarily remove it. By removing the hose now, when coolant isn't running all over the engine, you ensure that you can get it off quickly when you need to.

Now for the hard part. Stuff the rag under the short hose to catch most of the coolant that will leak out. Get two pairs of pliars. Use one to rotate the short rubber hose and the other to rotate the clamp until you can see the ends of the spring clips holding the tube on the long metal pipe. Move the spring clip inward (away from the end of the hose) by squeezing the clip with the pliars.

The trick is to get the short hose off and the long hose on the metal tube running beside the block as quickly as you can to minimize the amount of coolant that will leak out onto the engine.

Use the pliars to pull the short hose off the long metal tube beside the cylinder head. Put your thumb over the hole to stop the coolant from running out. Remove the long hose from the driver's side of the throttle body and attach it to the long metal tube. Now remove the short tube from the throttle body.

You should cut the long tube to fit its new location. That takes a third thumb to plug up the metal pipe while you cut the hose. When you are done, use the hose screw-type hose clamp to attach the hose to the long metal pipe.

Check the hose to ensure that it won't rub on the alternator or the serpentine belt and that it isn't lying on the (sharp) spring clamp ends holding the radiator hose on the engine block.

The first time you get a chance, put your hand on the intake manifold after the engine has run for a while. You will notice it is much cooler than an engine that still has the throttle body heater hooked up.

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Aftermarket Throttle Bodies

Q: Will a larger, aftermarket (52mm and larger) throttle body improve performance?

A: The stock throttle body flows about 630 cfm, which is more than adequate for any non-supercharged LT1/LT4. Even the higher flowing LT4 uses the same throttle body as the LT1, since nothing larger is required. The maximum airflow through a 350 at 5800RPM is only 587 CFM, and the LT4 maxes out at about 650CFM at 6200RPM.

Note that these figures also assume 100% Volumetric Efficiency (VE), which normally aspirated engines do not achieve. High performance engines run in the 85% area normally, and the only way to approach or even exceed 100% is to run a turbo or supercharger. Factoring in even a generous 90% VE, we would have 583 CFM of flow at the LT4 redline of 6400 rpm, and only 528 CFM at 5800 rpm. As you can see the stock 48mm throttle body which flows about 630 CFM is more than adequate for even the LT4! So, unless you are planning on supercharging or the like, the stock throttle body is good enough.

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-- Tires, Wheels, and Brakes --

Brake Coolers

Q: How can I cool the braking system?

A: One of the quickest and least expensive ways is to install the 9C1 and Taxi air deflectors on your Impala. These route more air to the brakes to keep them cooler and prevent brake dust buildup on the front wheels. The special 9C1 side deflectors were a later addition to the Caprice 9C1 package. From '91-'93 the 9C1 cars came without any side deflectors at all. In fact there was a factory bulletin that indicated that the stock type side deflectors should be removed if excessive front brake pad wear was noted (pads wear much more when overheated). In '94 they upgraded the 9C1 cars to full 4-wheel discs, and added the killer front brake cooling deflectors to increase front pad life. Besides the added cooling, they also lend a unique look to the front of the Impala, since the air dam no longer wraps all the way around the front of the car: the new deflectors start heading back at the ends of the spoiler underneath the radiator and the curves out, directing air towards the brakes. They are available for under $4 each at any Chevrolet parts desk, and bolt right up to the pre-drilled holes in the radiator housing.

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Brake Dust and Grease on the Wheels

Q: After I drive my car, there are spiral "arms" of dark brown substance that looks like grease coming from my center caps. What is this, and how can I stop it?

A: This can be one of two things: brake dust or wheel bearing grease. You can determine this by attempting to wash it off with a garden hose: the brake dust will come of somewhat easily without a lot fo scrubbing, but the grease will smear around and take some work to get off.

The brake dust seems to happen more often when driving in humid environments. It also may be related to the particular type of tire dressing that you are using.

If it is grease, you should get your car into the dealer to have them check to see if the bearing are lubricated and sealed properly.

One last possibility is that you used oil on your lug nuts when mounting your tires. You should not do this! Try to clean off the oil with brake parts cleaner and remount the rims.

Note that applying a good coat of wax on your rims when you wash your car makes it much easier to get all of this gunk off when you wash it the next time. The brake dust also seems to stick less to freshly waxed wheels.

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Tread Life

Q: How long will the stock BFG ZR4's last?

A: Under most normal driving conditions, including some enthusiastic driving, the tires will last about 30,000 miles. This has been stated by GM and BFGoodrich, and has also been confirmed by several list members.

When it comes time to replace them, you can usually find a good deal from Tire Rack. Look in the latest issue of Car and Driver or another good auto magazine for their latest add: the ZR4's are usually advertised for ~$140 each. If you get the tires locally, take in the ad and ask them if they'll meet the price: usually they will.

Another way to save money on tires is to join BFG's Team TA. Call 1-800-RACE-BFG and sign up. Ask them to send the rebate coupon. You can save $100.00 on a set of four. The rebate covers the ZR-4, and lasts from 3/1/96 through 11/30/96. Besides rebates, you can buy race tires (like the drag radial or R1's) for cost, which is typically $70-$100 less than the tire shops. They also send you a monthly newsletter with racing and tire tips.

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Brake Pads

Q: What sort of replacement brake pads should I use?

A: The stock pads on the Impala are very good. They stop well, don't squeak, and tend to last a long time. However, they are very expensive from GM. Also note that the replacement pads you get from GM are not the same as the original pads: they are of cheaper construction.

Raybestos makes a nice set of pads for the Impala. These are what Tim Allen used on his LT5 powered SS. Most auto parts stores should stock them. Make sure you get the top of the line pads as there are several grades available. Also note that the Impala pads are different from stock Caprice pads. Get Raybestos Premium Pads (Blue Box) , Part No. PGD 614 M.

Performance Friction make brake pads for Nascar and Indy cars. They sell "highway (-4)" and "z-rated" street pads for the Impala/9C1s. These are a carbon Metallic pad that can withstand higher temperatures to reduce fade and also last much longer than OEM pads. The "-4" front pads cost about $41.00 #6144 and the rears #6284 are about $47.00 a set. The "z-rated" pads are about $80.00 a set for the fronts and the rears aren't available yet in a Z-rated version. Thes pads put off a black dust as opposed to that rust color dust and should wash right off. Note that the "highway" pads are available from most AutoZone stores.

Note that Performance Friction will give 25% off list for any of the their products for NAISSO club members. As an example: Part #614Zm, (Front Z), list price is $84.90, which equates to a discounted price of $63.67! This is the best PF price you'll find! Contact PERFORMANCE FRICTION CO, MARK PRICE - Product Manager EXT #8143, 1-800-521-8874, 83 Carbon Metallic Hwy, Clover SC. You should mention "Impala Club" when ordering. Other useful product numbers:

There shouldn't be a problem with brake squeal as long as the rotors are properly prepared. Resurface and then sand them in a crosshatch pattern. 3M sells a sanding disk for a drill designed to put the crosshatch pattern on the rotors. The outboard clip needs to be crimped and the inboard grasshopper clip should be replaced with a new one.

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Tire and Wheel Sizing

Q: What size is the standard wheel and tire combo on the Impala SS?

A: The standard tires are BFGoodrich Comp T/A ZR4s in the P255-50ZR17 size. Currently, BFGoodrich is the only company to make a tire in this size. Several tires are available in similar sizes, but the speedometer will then be off.

The B body cars have a 5", 5-bolt stud pattern, while ALL Corvettes (and most other sports cars) have a 4 3/4" 5-bolt pattern. Keep this in mind when purchasing aftermarket wheels or drooling over those 315 series tires on the 'Vette.

The stock 255/50 17's are 27.0394" in diameter (the height of the tire itself, or the height of the aspect ratio, is 5.0197")

And finally, the magic formula:

Rim Size[in] + (((Width[mm] * (AspectRatio / 100)) * 0.03937)*2)

17 + (((255 * (50/100)) * 0.03937) * 2)
17 + (((127.5) * 0.03937) * 2)
17 + ((5.0197) * 2)
17 + 10.0394
27.0394" for the stock setup.

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Threshold Braking and ABS

Q: Is the ABS system on the Impala safe? What about this threshold braking business?

A: Threshold braking is a technique practiced by all serious high performance drivers; if made a habit, it replaces the `stab the pedal and lock 'em up' panic habit entirely, and is much to be prefered. Basically, the premise is that tires generate maximum braking force when they have just started to slide, but just before the wheels lock up entirely. Drivers who threshold brake learn to feel what this `threshold' feels like, and learn to search for it and hit it on the application of the brake pedal. In many cars, you can feel that you are near the threshold when the pedal starts to firm up as you depress it. In any case, if you can't hear the tires whine just a bit, you're not very near the threshold.

In some cars with ABS, there is a twinge in the pedal just before the system starts cycling; if the driver backs off on the pedal just a tad when the twinge is felt, then they are very close to the threshold and they'll probably achieve better stopping distances than if they just punched it and let the ABS take over. This method is primarily useful in early ABS systems; newer ones with more sophisticated multi-channel controllers do not require such methods.

Recently, there has been a rash of publicity over a number of accidents, and one death, involving police cars equipped with ABS systems. The police departments in question quickly blamed the new ABS systems, but according to Autoweek magazine, it now seems clear that the problem was a lack of training; none of the involved officers had any recent performance driving training. There is reason to believe that the drivers reacted to the pulsing brake pedal by `pump braking', an old and discredited technique of stabbing and releasing the brake pedal, the goal being to try and get brakes back with a failing hydraulic system. If you think about it for a minute, you'll realize that pump braking must cut the effective operation of a working brake system by at least 1/2, so if you cut the 40% duty cycle of an ABS system by that much, you are giving up most of your brakes for the wrong reason. Threshold braking has the advantage in that it is an effective and useful technique regardless of whether your car has ABS; if you do fear a failed hydraulic system, then one or two stabs at the pedal will be sufficient.

ABS works by monitering the wheels of the car, looking for signs of locked brakes. The Impala system can distinguish between thre different points: left and right front and rear. It cannot detect impending lockup (which is what you would really want in an ideal world), but only the existence of lockup. The sensors used vary; some of the less well designed sensors are sensitive to tire size, and to brake pad material, and may cease to function properly if the owner deviates from original equipment or OE-equivalent components.

When the sensors detect lockup, the ABS system responds by unlocking the brakes individually. If the driver keeps their foot firmly planted, the ABS will end up cycling between the locked and unlocked states (if a sensor existed that could detect _impending lockup_, then we could sit right at that point, which is where maximum braking effect is achieved.) This pulsing can often be felt in the brake pedal, as the system cycles. The percentage of the time that the brakes are truly engaged is called the `duty cycle'; typically in an ABS system this is about 40% With older systems and on dry pavement, a trained driver could beat this duty cycle quite reliably using a technique called threshold braking, but newer "multi-channel" systems appear to be able to beat threshold braking system in at least some cases. on wet pavement, braking is so chancy that ABS will outperform threshold braking nearly every time. However, in some mud and snow conditions, often maximum braking effect can be acheived with the brakes locked; only Audi, of the manufacturers producing ABS-equipped cars, has seen fit to provide a disable switch for the ABS system for this eventuality.

A particularly important feature of ABS is that it preserves steering control. Without ABS, once the brakes are locked, steering is impossible, but with ABS, it can be retained because the ABS system will release the brakes if it sees steering-triggered lockup, and back off on the percentage of the time that the brakes are applied. Braking distances will lengthen accordingly, but at least you will be able to steer the car.

An important caution: ABS cannot exceed the maximum theoretical braking force in any given situation; if you start sliding on glare ice, don't expect an ABS system to help you out very much. The coefficient of friction is not changed by the presence of an ABS system in your car.

As far as maintenence goes, in addition to the potential restrictions I've listed above, you have to worry about the following: 1) parts costs are much higher; the OE master cylinder for my obscure european sedan lists for $185, but the OE master cylinder for the ABS-equipped version of the same car lists for over $1000. Most manufacturers explicitly forbid use of DOT-5 (silicone) brake fluids in ABS-equipped vehicles. Because of the potential cost of replacement of corroded brake system components, regular (I suggest annual) replacement of brake fluid becomes very important.

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Wider Wheels

Q: I'd like to get some wider wheels for the rears. Where do I look?

A: You may want to get wider wheels if you plan to run 275mm width tires or larger on the rears. These are really too big for the stock wheels, according to most manufacturers.

The Forgeline RS (used by Callaway) and the ZR6 made by ROH apparently closely resemble our stock wheels and are available in 9.5 x 17. The ROH (an Australian company) rep says ROH had the contract to make the OEM wheels for our SS, but then GM switched to Superior Industries International in Van Nuys, CA. The SS prototype shown at car shows had ROH ZR6 wheels.

Forgeline RS's run around $495/wheel, but that may be negotiable. Expect around $250 a piece for the ROH's. As a basis of comparison, your local Chevy dealer will sell Impala rims for $330.30 each, including centercaps. The aftermarket wheels will fit perfectly as far as bolt pattern and backspacing.

There are also several places in the US that will cut and widen the stock wheels. Try "The Wheel Shop", and expect to pay around $200 per wheel.

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Winter Wheels

Q: I'd like to get some decent looking wheels to put on my Impala for the winter. Any ideas?

A: Standard Caprice rims will not clear the disk brakes. You need to use the 9C1 (RPO N97) rims, or some other type of steel rim that will clear. The Impala takes a standard 5 x 5" spacing wheel. GM offers several alteratives, such as S10 wheels (look especially sharp with the baby moon chrome hubcap covers) or "G" van/truck wheels (heavy duty, look good, and clear everything).

If you use a regular steel wheel with less than 4 1/8" backspace the wheel will bind against the caliper when the lugs are tightened and the wheel will not turn. For instance, if you are using S-10 rims for the winter, you should get 1/16" spacers to go between the rim and hub so the wheels will turn. That is where the 4 3/8" (or greater) back space comes into play. If you examine a stock steel rim, it consists of several "steps". Each step is smaller in diameter. The smallest diameter is where the center section (where the lug bolt holes are) is welded to the rim. The police (9C1) rims are 7" wide by 15" rating. They fit our cars because the backspace is held at 4 3/8". This allows the step in the steel rim to come as close as practical to the caliper without touching it. The disadvantage to Impala SS owners is that as you go wider on the rim width virtually all the extra width has to go toward the outside of the car. Anything over an 8" rim will take the tire sidewall and bring it out to the fender/body metal causing contact (read: tire / body damage). Using a 17" rim there is sufficient clearance for the rim to go over the caliper and sufficient clearance for the rim to grow to 9.5" (with 5 1/16" backspace) and still have clearance to the frame and inner fender well to allow a carefully selected oversize tire to clear.

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-- Interior --

Alarm Systems

Q: What alarm system does GM recommend installing?

A: Goodwrench has several alarm systems that can be installed in the Impala:

  1. VSS 100 (economical)
  2. VSS 150 (new and unrivaled)
  3. VSS 200 (high tech)
  4. GM Goodwrench VSS 250 (new with high tech features)
  5. VSS 350 (All new top of the line)

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Seatbelt Guides

Q: The rear seat belts are very uncomfortable for my children: the shoulder strap hits them right in the face! What can I do?

A: 97+ Chevy Blazers have a seat belt guide for children that redirects the rear seat belt so that it will go across their shoulders at the correct angle and not ride against the side of their neck. The part is basically a plastic clip that attaches onto the seat belt and a short four inch bungee cord attached to a push in plastic fastener and holder for the clip part. The best part of these GM guides is that they can be clipped on the seat belt and removed very easily to accommodate for children or adults. When the guide is not in use it can be securely attached on to its holder fastened with the same fastener that is holding the bungee cord.

Installation is a snap but should vary according to the size of your children. On my Caprice there is a plastic interior piece covering the transition from the back of the seat to the door opening. I drill down about one inch from the top screw hole in the center of the plastic piece. Drill a hole large enough to accommodate the plastic push in fastener, then just put the fastener in the hole and push in the securing pin on the fastener. Wherever you install the clip, just make sure there is enough of a empty space behind the area you are drilling into to accommodate for the depth of the fastener. Part numbers are as follows:

Part  Number    Description    List Price    Naisso Price*
15986626         Guide             3.00            $2.19  Beige
15986628         Guide             3.00            $2.19  Blue
15986623         Guide             3.00            $2.19  Graphite
15986624         Guide             3.00            $2.19  Gray
*via Bob at World Parts
You could also add one of these guides to the front passenger seat by attaching it to the center door pillar interior plastic. DISCLAIMER: Perform and use this information at your own risk. I take no responsibility for the safety of your children or any other individual for that matter.

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Changing the Factory Carpet

Q: My factory carpet is looking shabby. I'd like to replace it with black instead of the easily-dirtied light grey. Any suggestions?

A: Use the factory black carpet for a Cadillac Fleetwood (the Roadmaster carpet is the same as the Caprice). This stuff is MUCH higher quality than the Chevy/Buick carpet, plus only the Fleetwood had black available. It is fully complete with insulation and sound deadener, more than what comes on the stock carpet. The pile is much denser and slightly longer than the stock Impala carpet as well. The Fleetwood has a 6" longer wheelbase, so the carpet will have to be trimmed somewhere during the install. You can either slice it across between the B-pillars under the seats and overlap, or possibly trim the rear section only. The floorpans are basically the same except for the 6" in length, so other than some minor trimming, it should work fine. The Black Fleetwood carpet is available under part number 10276338 and costs around $370 list, $263.12 wholesale complete. You can also add the nice black Fleetwood floormats: 12370406, Mat pkg front, $36.23 and 12370406, Mat pkg rear, 20.80.

A worthwhile addition if you are adding the Fleetwood is to add the rear passenger heating / cooling system from the 94-96 Fleetwood as well. You need a Distributor (010164972, $10), a RH Outlet Duct (010164974, $13), a LH Outlet Duct (010164975 $13), and Duct Retainers (020030401, 2 needed, $1). The total price should be around $40. These pieces allow you to run ductwork through the factory slots in the Fleetwood carpeting to get air conditioning and heating to the rear passengers.

If you are having problems with your carpet (unusual wear, holes, etc.) and would like the dealer to replace it with the Fleetwood carpet, follow these steps:

  1. Have your local dealer inspect the carpet and ask that it be replaced under warranty. The dealer will readily agree to replace the carpet under warranty providing the warranty period has not expired. Some dealers have tried to deny warranty saying the wear is normal. Don't you believe that or accept it. The warranty applies as long as the warranty period has not expired. The dealer may state that they will replace it in kind, warranteed part for warranteed part, with no deviations. This is the GM line the dealer is held to. Any deviations from this policy will result in the dealer losing any reimbursement by GM for warranty

  2. If you want better carpet than stock, contact GM Customer Service to request replacement, under warranty, with the Fleetwood carpet. Volunteer to participate in any additional costs to cut and seam the carpet to fit the SS floorpan or for additional costs for parts to install the air diffuser which diverts warm air to the rear footwells. Point out that the Fleetwood carpet is $12 cheaper than the SS carpet, based on list prices. GM Customer Service has agreed to this provision for others.

  3. If and when GM agrees, they will ask for the dealer's name, phone number and the Service Manager's name. Have this info handy.

  4. Find out from the dealer if they do the work or subcontract it to a local upholstery shop. GM normally allows $150 for a B-body carpet replacement as reimbursement to the dealer. If it costs more to fit the Fleetwood carpet to the SS floorpan, you will be responsible for the difference. If the dealer uses a local shop vs. their own shop, visit the shop, show them the car, tell them it will have to be cut (with an approx. 3" section taken out), seamed and fitted to the floorpan. If it is cut and seamed under the front seats you cannot see the seam. They can provide you an estimate and this will give you a pretty good idea of what your participation will be for the additional labor.

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Adding a CD Changer

Q: My Impala came without a CD changer. Is there an easy way to add this?

A: If you have a 1995-1996 radio with the cassette player only, it is relatively painless to add a CD-changer, and allow the stock head unit to control it. The CD player radio will not control the CD changer. Also, '94 radios were different and cannot control a CD changer.

If you are looking to buy a changer, contact World Parts or call Speedometer Services in Georgia (1-800-241-2385) to get the stock factory changer for dealer cost (currently about $410). The connectors should wire right into the stock radio with very little pain.

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Compass/Electrochromatic Mirror

Q: I want to install a compass. Is there a good way?

A: Option DD7: "Mirror, Inside Rearview, Electrochromic w/Digital Compass". This is a direct replacement factory rear view mirror that includes a digital electronic green LED compass display in the upper right hand corner. It is a self contained unit, with a fluxgate sensor mounted inside the base of the mirror where it attaches to the windshield. This mirror also includes a built-in electrochromic feature, which causes the mirror to automatically darken at night when headlights shine brightly from behind. Both the electrochromic and compass features can be turned on and off via a switch on the bottom of the mirror. It is available as P/N #12344614 and lists for around $265.

There is a hot at all times circuit to the Impala mirror which must be cut or disabled. This hot lead and the dome light circuit relay ground are wired to pin 7 and 6 of the original mirror. The compass mirror only uses pins 1, 2, and 3 which carry the power for the mirror and compass (hot in run, bulb test, and start), ground, and a hot in reverse signal (from the backup light circuit) to nullify the electrochromic feature while backing up.

P/N 12344614 comes with an instruction sheet that details the wiring. It also includes an extra 3-pin connector which plugs into the mirror. The new mirror uses only these 3-pins (pin 1, 2, and 3 at the mirror), yet the stock wiring harness in the Impala has a 7-pin connector to the mirror with the 3 pins for the electrochromic function plus two extra pins for the 12v (hot at all times) and ground for the map lights.

The compass mirror will take the stock 7-pin connector if you cut a small section out of the back allowing the larger connector to be inserted. Then take pins 6 and 7 and moved them to location 4 and 5 in the stock connector which has no corresponding pins in the new compass mirror. This functionally disconnects those leads from the mirror, yet they were still in the stock connector and I did not have to cut any wires.

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Installing a 96 Console in a 94-95 Impala

Q: Can I install the floor shift console from a 96 into a 94-95 Impala?

A: Scott Mueller provided this article on how he did it. He'll have a more detailed instructional guide available later, which will go into the tech archives, but here's a quick rundown for you impatient types.

Parts list and approximate prices:

You'll also have to make a bracket or block to mount the shifter to the floor. The factory bracket on the '96 is not available as a separate part. However, you can make a thick spacer block out of solid 3" thick plastic to bolt the shifter to. It had to be ground to fit the floor contour as well as the shifter. Bolts then attach the shifter to the block, and then long bolts go through the block to the floor. Use all stainless hardware to prevent corrosion, and large stainless steel washers sealed with silicone sealer. The holes end up above and to the rear of the trans, and are not visible unless directly under the car looking over the trans.

You will also need to grind down the '96 style shift lever you will install on the trans shift stud as well as the original shift lever so they are half of their original thickness, such that they can both go on the stud together. This is so that when you move the floor shift, the stock original linkage will also move, rotating the shift collar on the column and moving the gear indicator.

As an alternative, I believe that the shifter bowl from an '87 Monte Carlo will work, it does not have the shifter attachment boss, but should be a direct replacement for the stock one otherwise. In otherwords, it will rotate so you can have a functional gear indicator. I have not tested the Monte Carlo shift bowl so I am not certain it will fit, but I have one and will be installing it also on my '95 9C1 later this summer, at which point I will be fully documenting the best procedure for doing the shifter.

Using either the original shift bowl (with the shifter boss ground off) or the Monte Carlo bowl also preserves the neutral safety switch in the column. You will have to remove the steering column, remove the column shift lever, grind down the lever mount, bondo or tape the hole, and paint to match.

Converting to the '96 neutral safety on the shifter is much more expensive, as is purchasing all of the lower steering column parts up to the shift bowl from a '96. Since many parts are different in the column, it doesn't make sense to go to the '96 column configuration. If it works, the Monte Carlo bowl will be the perfect solution, except that there is it is a lot of work to dissasemble the column to replace the bowl, rather than remove the entire column intact and grind off the existing shifter attachment and fill the hole with bondo.

You can move the BTSI (Brake Trans Shift Interlock) solenoid over to the console, or just disconnect it. Tricholoroethylene removes the "Press brake to shift from park" writing on the console cover plate without damaging the plastic. You will also need a few misc. pieces of hardware and a light socket for the console shift indicator. I think it was about $700 in parts total for everything.

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Installing an External Trunk Opener

Q: I saw a Caprice with dual switches where my lighter is. What gives?

A: This is option 6H6: "External Trunk Opener, RH side of Radio". This is a dual switch panel that replaces the cigarette lighter outlet to the right of the radio in the dash. The switches are backlit and match the shape and size of the dual switch panel to the left of the radio. The top switch is an on-off switch that is normally wired to cut off the speedometer and radio display in Police vehicles. This was designed to eliminate any interior light with the car running for surveillance purposes. You could wire this switch to enable or disable the signal to the power antenna relay, allowing you to play CDs (or tapes) with the antenna remaining down. With the switch on, the antenna will go up and down when the radio is turned on as normal. The second switch is a momentary contact power trunk release button, which functions in addition to the one inside the glove box. The cigarette lighter itself is relocated to a hidden blank area in the dash, which is visible only with the ashtray pulled out, as per the SEO Police package.

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Fuel Gauge Problems

Q: My Impala ran out of gas the other day, and the gauge still said I had some and the low fuel light wasn't on. What's up?

First, it's not a good idea to run the gas tank too low (into the red). The fuel pump in most modern cars is cooled by the gasoline in the tank, and if it is not submersed, it will overheat and burn out. You can still have gas left and uncover the pump due to fuel sloshing.

TSB 67-65-19 describes a condition where the vehicle stalls or runs out of fuel while gauge shows fuel remaining. The fix is to repair or replace fresh air hose/canister and bracket. The fuel vapor canister fresh air system may be restricted. Basically, if there is a kink in the fresh air hose to the purge canister or if the canister itself is plugged, you'll draw a vacuum on the gas tank and fuel won't be able to flow. It's kinda like trying to pour gas out of your gas can without opening the little vent. This applies to 94 and 95 Impalas only.

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Horn Problems

Q: I have to press very hard to get the horn to work. Is this normal?

A: The later models received a revised horn pad. This pad can be identified because it has two "bugles" on the cover rather than one. It is much easier to activate the horn using this design. A technical service bulletin exists to have this fix applied to '95 Impalas if they suffer from "tilt-n-toot". This means that the horn activates when the tilt steering is released forcibly. With a little coercing, most dealers will put the new horn pad in any Impala as a safety item.

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Inflatable Lumbar Supports

Q: Is there a way to improve lumbar support in the Impala seats?

A: You can buy an inflatable bladders, complete with inflator bulb and bleed-off valve, from upholstery supply houses, JC Whitney, or many other sources, and for around $10. When you get ready to install, run the driver's seat all the way forward, then lean the seatback all the way back. You'll then see two plastic edge moldings that hold the front and rear seatback leather together, and they simply unsnap when you run a tool (such as a screwdriver) between them. Once that's done, run a hand up between the leather seat upholstery and the foam padding behind it. You'll encounter a little resistance, because the two are Velcroed together. Simply undo the Velcro with your hand, and you'll be able to insert the lumbar bladder into the space. Don't close up the seat upholstery yet: instead, return the seat to its original position, and check, by sitting down, the position of the bladder. It should, when pumped up, press into the center of the small of your back.

Adjust for fit, and then close up the plastic junction. Run the tube for the inflator bulb down and around to the right of the seat, and position the bulb forward of the seat belt buckle between the seat's thigh bolster and the console.

If you are willing to spend the money, an even better solution is to use the swap the pseudo-buckets in the Impala with a set from a 93+ Bonneville SSEi. The seats have one nut in each corner that is welded into the seat bottom that accepts a bolt coming up through each corner of the adjuster. These nuts in the Bonny seats are about 1-1/4" closer together (side-to-side) than the Impala ones, so to use the stock adjusters, drill a 5/8" hole in each corner, 5/8" inside the stock holes. Alternatively, the welded-in nuts in the seat could be removed and moved further apart. Other than the four totally hidden holes, it is a straight bolt-in. The power seat connectors hook up stock, and an extra power cable will enable the controls on the side of the seat. Take the headrests to a local upholstery shop to get the "SS" embroidered in for the totally stock look. logo.

The '93 and up Bonneville SSE and SSEi offer virtually identical seats in leather, with gray or beige being the only color options. The option code is AS7. The gray leather is a perfect match. If you can find a wrecked '93 and up Bonny with gray leather buckets you've got yourself one nice upgrade. You can go one better if you can locate a set of these with adjustable lumbar supports.

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Floor Mats

Q: Where can I get some nice mats for my Impala, preferably with an Impala-specific log on them?

A: Call Auto Custom Carpets in Alabama. See the latest NAISSO newsletter for discount info. The mats, front and rear, are heavy black carpet with good edge stitching. You can order them in many different configs, such as an Impala deer logo alone embroidered in silver on each mat. You can also get the Impala SS script alone or with the logo. The mats do not move around. They have little nubs on the bottom. The cost is a little more than $100.

You might also try the Griot's Garage catalog (worth getting even if you don't want the mats!). They are in Tacoma, WA at 1-800-345-5789. They sell a set of 4 mats with custom logos for $98-120, and they are available in smoke, quartz, grey, black, and others. As of last yearm, their vendor didn't have any 94-96 Impala logos. The quality is very, very good.

Motorcars International (Springfield, MO, 1-800-977-9707) also sell custom mats, same identical colors as Griots, and say "there isn't a logo that they can't do". A set of 4 with logos runs $124.

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Resetting the Change Oil Light

How do I reset the Change Oil light? Or, I've just changed my oil and the light comes on. Do I need to change it again?

A: The '94s have a button behind the panel on the left hand side of the dash. Open up the panel, and with the car in the "On" position but not running, press and hold the button until the light goes off.

All Impalas can use the next method. With the car in the "On" position but not running, press the accelerator to the floor three times while the instrument panel is going through the bulb test stuff. The Change Oil light will blink indicating that it has been reset.

You are supposed to reset the light manually after each oil change. If you do this, you'll probably never see it. However, if you don't, it may come on after a certain number of miles indicating you need a change. Just reset it: your oil is fine. Also, keep in mind that most mechanics (GM service technicians included!) do not reset this light when they change oil!

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Oil Pressure Gauge

Q: Why does the oil pressure gauge always read 3/4?

A: The stock SS oil pressure gauge is completely bogus, since it actually does not use a sending unit but a switch instead. The oil pressure switch is mounted on the back of the engine behind the intake manifold, and is calibrated to close at 4 psi. When the switch closes, it grounds the stock oil pressure gauge through a 68-ohm resistor, which causes the gauge to read 3/4 scale at all times. Factory SEO (Police) cars get a real sending unit calibrated to show a resistance between 0 to 88 ohms depending on actual oil pressure. You can install this yourself if you're so inclined.

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Use Overdrive in Pursuit

Q: What is this "Use Overdrive in Pursuit" sticker I hear about, and where does it go?

A: Early (pre-94) police package Caprices were equipped with a sticker that read "Use Overdrive in Pursuit Mode", or something to that effect. The sticker is available from the GM parts bin and makes an interesting conversation starter in the Impala. The stock location is under the instrument panel plastic just above the steering column. However, this location is not usable on at least the '96 cars. Another alternative is just below the Impala emblem and above the radio.

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Overhead Console

Q: Can I get an overhead console for my Impala?

A: GM offers one for their small S10 Blazers that might work. A better solution might be an aftermarket unit from Gall's or Infinity. Gall's was carrying an overhead console with 6 switches, an eyeglass compartment, two map lights, and a small storage compartment in the back. It looks identical to the console offered by Infiniti Products for Chevy trucks. It is only for 91-96 Caprices, and was $229. Call Infinity and ask if their Traveler Console would fit Impalas/Caprices as Gall's appears to be identical to theirs. Infinity offers a compass/temp option but the switches may be more useful. Jobber cost from Infinity is $131.69 and $16.95 for six switch option or 187.39 for the compass/temp option. Gall's is still carrying it but not showing it in their new catalog. Infinity's phone number is 1-800-217-7133.

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Buzzes, Rattles, and Creaks

Q: There are a bunch of buzzes, rattles, and creaks inside the car. Any ideas where to look?

A: First, look for any obvious loose pieces of trim and tighten them down. The quality control on the interior bits is a bit lax.

If you have rattling from the door panels, it could be problems with the power window motors. Several people have found that the rivets holding the motors to the doors were loose and needed to be re-riveted.

If you take the door panel off yourself, there are several areas that can cause rattles. One is the sheet metal itself. Purchase some rubber/asphalt sheeting material specifically designed to sound insulate a car. This stuff goes under different names, one manufacturer calls it Dynamat: most stereo places will carry it. The stuff comes in different sized sheets that can be cut to fit virtually any panel, and has peel and stick adhesive on one side. Attach pieces inside of the door panel outer skin.

The next area of rattles is the door lock module itself. Some of the rivets in the lock module may be loose from the factory. You can remove and replaced any or all of the rivets there. The lock module bracket is held in place by 4 special aluminum rivets (p/n 9442468, cost 0.24 each).

Also running from the lock module to the door handle are two metal rods, which were close to contacting several parts of the door or each other either with the handle relaxed or pulled. You can wrap these rods in two or three places where contact may occur. You can also tape the handle area, where one of the rods may be near contacting. Finally, some minor bending of the rods will insure that they will clear everything properly.

Another area of potential problems is the window regulator mechanism. Check this out and made sure everything is tight. Note that when the window moves up and down it places stress on other parts of the door, so even though your rattle went away when your window was partially opened, the rattle could still be caused by the lock mechanism or other area of the door.

Finally, when you re-assemble the door, add extra silicone grease to the door lock module, the door handle, and the clip that the rods slide through. Also stuff foam into the door armrest area and under the switch pod. Add some thin foam pieces behind some of the wiring harness connectors and wires to make sure they will not contact the door metal.

If you're getting a buzzing sound during acceleration from the steering column area, purchase a can GUNK heavy duty silicone lubricate spray and lube the "cube" of plastic which is located behind the blinker control adjacent to the tilt wheel adjuster. Also, lube the whole steering column and its associated mechanical parts including the blinker control, tilt wheel adjuster and ignition locking cylinder.

Rattling noise from RH rear trunk area. Noticeable during cold ambient temperatures. If the noises are coming from the trunk, pull back the side trunk carpet. Stuff 2-3 old towels in the cavernous area between the rear wheel well and rear door pillar. Take a long pole or yard stick to pack or stuff the towels into the cavernous area. Then take another towel and pack it in between the right side of the wheel well next to the rear quarter panel back to the tail light assembly. Then pack 1/2" to 1" of foam padding along the quarter panel. Reinstall the carpet. You may want to do this on both sides. Finally, to clean up the trunk area, purchase the 9C1 trunk mat to help keep things from siding around during an aggressive turn.

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Speaker Upgrades

Q: How would I go about upgrading the speakers in the Impala?

A: Just about any speaker would be a tremendous improvement over the weak GM units. Upgrading the rears is easy:

If you use 4x6's to replace the factory front speakers, then you do not have to completely remove the door panels. The factory 4x6's are mounted on a removable plastic baffle. If you remove the two screws in the armrest (you don't have to remove the armrest, just let it sit there), one screw in the bottom rear of the door panel, and pry out the three door panel retainers along the bottom of the door panel, you will easily have enough access to the baffles to remove them. You can then transfer the factory speaker wiring (96's have about 10" or speaker wire, ending in a two-pin speaker connector) to the replacement speakers, mount the new 4x6's into the original baffles, and reinstall them. This allows you to do all of the work outside the constraints of the doors.

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Steering Wheel Alignment

Q: My steering wheel is misadjusted. Can this be fixed?

A: There are two common complaints with the steering wheel on the Impala: one is that it is off-center or angled in the dash, and the other is that the wheel is not horizontal when traveling in a straight line (i.e the top of the wheel is not at 12 o'clock).

The first problem appears to be a permanent problem. No one has found a way to fix it yet. If you have a '96, the problem may be exaggerated by the black bezel surrounding the steering wheel: it is cut out deeper on the right hand side which makes it appear as though the wheel juts off to the left. This is a relic from the 94-95 column shifter, and is normal.

As for the second problem, you should first have the vehicle aligned. The factory alignment is notoriously poor ("toe-n-go", as one member witnessed at the factory plant), and can cause the car to pull to one side or another. If this does not fix it, the dealer can reposition the steering wheel so that the wheel is perfectly horizontal while traveling in a straight line.

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Sungate Windshield

Q: What is the SunGate windshield, and what does it do?

A: The SunGate winshield has tiny metal particles in it to prevent the sun from beating down into the car and onto the dashboard as much. You can tell if you have the SunGate by checking for "Sungate Shaded Solar Ray" on the lower passengers side of the window. It was RPO A23 in 1995 and 1996, so you can also check the SPID label on the underside of the decklid to be sure. An unpleasant side effect of the SunGate window is rendering most radar detectors useless.

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Q: What sort of sunroof should I get installed in my Impala?

A: Lennie Dolphin has a fully automatic sunroof by the American Sunroof Company (ACS) which the dealer installed as an after market option.

The sunroof is priced at a cost of about $900 and has the vent mode with a wind deflector. Push the open button, the roof opens. Push the vent button, the vent opens (great in the winter for a little fresh air without freezing yourself). You have the option of many different positions from about 1/4" opening to full. The panel, which matches the headliner, can be closed to keep out the sun or slid back to see the stars at night. When I open it, the panel will slide back with the sunroof. The controls are mounted in the headliner just above the rear view mirror. When I shut off the engine, it automatically closes. You also have option to lock the sunroof to keep it open or vent after shut off. Excellent install, no leaks, just fun to have and use.

You can see a picture of the sunroof at Washington Area Impala Lover s (WAIL) Homepage, or you can contact ASC at:

American Sunroof Company
18900 Walnut Street
Southgate, MI 48195-9800

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Installing Auxiliary Switches

Q: I have a need for some additional switchgear inside the Impala. Is there a good looking way to do it?

A: The police package has a dual switch panel that goes where the cigarette lighter is in the stock Impala. The top switch is labelled "Off" and the lower one is the trunk momentary contact switch. The cigarette lighter is relocated to the ashtray. P/N for the switch is 10225158 (about $25). You may also want an 8 way Female Metri-Pack 150 Series Terminal (old P/N was 12064862: you are more likely to find it as P/N 12126438) for connecting the switch to the wire harness: it lists for ~$90. This connector is shown on page 8A-202-12 of the '96 Impala service manual. The "F Metri-Pack 150 series" designates the actual types of terminals used in this connector as Female Metri-Pack 150 series. That info will be needed when you go to order the terminals: you can then use whatever wire you want. Note that removing the radio (take the screw out on each side of the face plate) gives easier access to the switches and the antenna wire.

Please note that the '96 ashtray is different than previous years. There is an extra set of stops on the ashtray rails to prevent is from coming out too far and interfereing with the console shifter or your fingers. To remedy this, remove the whole assembly, take the ashtry out of the mount (just lift the clips on either side) and use a Dremel tool with a cut off wheel to remove the the first set of stops. These are the ones most toward the rear of the car when the tray is installed. This will allow the ashtray to come out about 1" more and allow the lighter to be used or a cell phone (computer) adapter to be plugged in. Just be careful when you slam the shifter into park: if the ashtray is out, you've only got about 1/2" of clearance between it and the shifter handle.

There is a big, ugly yellow button in the police Caprice that takes the place of the change holder in the Impala. A nicer option would be the panel that goes in the spot on wagons (P/N 10203772): it contains an on/off switch for the rear wiper and a momentary contact button for the hatch release.

If you still need more room, several companies have permanently sealed the ashtray shut and mounted rockers on top of it. This could be handy for many things, and slid out of the way to use the cupholder.

Although it's not a "true" 6H6 style switch and it does not replace the cigarette lighter like the real 6H6 style switches, altering the E/M/RESET switch may be an effective alternative. This can be handy if one needs an extra factory style on/off type switch without having to cut extra holes in the dash for it. Inside the E/M ("English to Metric" or miles to kilometers) switch, the pink and light blue wires going to it control the top ("E/M") button. This top button is an on/off style switch. The light green wire controls the bottom ("TRIP") button. This bottom button is a momentary contact switch. In this particular switch, the light green ("TRIP") wire momentarily makes contact with the pink and light blue wires ("E/M"). As you can see, the switch differs from the "true" 6H6 switch because it does not have the switch circuits working in conjunction with each other like this one does. It is for this reason the bottom ("TRIP") will have to remain dormant and not used if the top ("E/M") switch is to be wired up for use. This is due to the fact that a closed circuit will occur between ALL the wires in BOTH circuits when the "TRIP" button is activated. This may pose problems for those who choose to wire an accessory to the light green wire associated with the "TRIP" momentary contact switch. The solution is the following:

  1. Have the pink and light blue wires spliced together permanently. This will allow the dash to read in English measurements (miles).
  2. Next, the green wire needs to be connected to a pin on a momentary contact switch (like the "trunk" button on the "true" 6H6 switch). The other pin from that momentary contact switch needs to be connected to the permanently spliced pink and light blue wires.
  3. Wire in the new accessory to the "E/M" switch via the PINK and LIGHT BLUE wires on the connector going to it.
  4. For backlit illumination, do not touch and keep the light gray and black wires connected.
  5. Swap the "TRIP" button itself from the E/M switch with the symbol for "TRUNK" on the 6H6 switch. This is accomplished by easily disassembling each switch. Just unhook the tabs from the back of each switch, take out the buttons (easy) and swap them out of each other. Now the correct button for "TRIP" will do what it actually says. (Reset the "trip" odometer).
  6. You can also switch the circuit boards between the EM/Trip switch and the real 6H6 switch. This will allow you full isolation of the top and bottom switches. The circuit boards (but not the bezel!) are interchangable.

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Installing a Tachometer

Q: Is there any way I can mount a tach in the Impala?

A: You can fairly easily mount a 2 1/16" tachometer in the black bezel that surrounds the instrument cluster.

Cyberdyne (1-412-258-8440, 1-412-258-8442, fax:1-412-258-8342) gauges are digital, featuring red LED displays. They have no logo of any kind, which contributes to the "factory" look, and are completely dark when the vehicle is off. These are 2-1/16" round gauges with black bezels and you can install them directly into the black dashboard instrument cluster bezel on either side of the steering column.

Alternatively, you can get almost any analog tachometer that is less that 3" deep and 2 1/16" wide and mount it in the same location. JC Whitney carries a unit (81NP1446W) that does the job nicely: no writing on the face, black bezel, and backlit.

You can also use the two screws that hold the black instrument cluster bezel in place as mounting points for a tachometer. For instance, you could mount the base to one of these screws and turn the face upside down. It would restrict a bit of the instrument cluster, but it would still be useful. Alternatively, you could mount a bracket between the black bezel and the dash housing that would stick out past the bezel. The tach could then be mounted to the top of this, which would put it above the dash and out of the way of the instrument cluster. Wires can be routed back through and around the bezel.

Greg Day is now making "A" pillar gauge pods. They should be available to ship in about two weeks, and can be purchased from Summit or any speed shop that carries the Keystone Catalog. The units are paint matched to our interior gray trim color. The part numbers are 10231 (Single 2" gauge pod), 10230 (Dual 2" gauge pod), 10231 (Single 2" gauge pod), and 10232 (Single 2 5/8" gauge pod). Pricing should be between $20.00 to $25.00 each Some shops may not recognize these numbers yet as they are new items. You can also contact Greg Day at Gauge Works 703-404-1166.

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Temperature Gauge Problems

Q: My temperature gauge shows my Impala running really cool, like in the 150-160 degree range. I thought the thermostat was for 185. What's the story?

A: The gauge is functioning exactly as it is designed. The temperature indicated by the gauge is absolutely and totally accurate, for the position on the engine that the sending unit is mounted!

To understand this, first note that there are two temperature senders on the Impala. The one on the RH cylinder head is for the gauge only, while the one on the front of the engine in the water pump is for the PCM.

Now remember that this engine is reverse flow cooled. This means that cold coolant entering the engine from the radiator is directed to the heads first, which is exactly why the gauge sending unit reads low compared to what the PCM sending unit sees. The PCM sending unit sees actual engine coolant temperature, and is not hit by the flow of cold coolant directly from the radiator.

If there is a problem with the gauge at all, it is certainly not that it is inaccurate. Nosir, the gauge is perfectly accurate, but the sending unit for the guage is mounted in the WRONG PLACE to get a "correct" reading. Unfortunately there is no other tapped hole in the water jacket to mount it unless you drill and tap another location. There is a tapped and plugged hole in the other head, but that would offer the same gauge readings: in fact, it might read even lower temperatures since it is mounted more towards the front of the block, closer to where the coolant first enters from the radiator.

It has been verified with scan tools that can directly read the PCM temperature sending unit, as well as a digital Cyberdyne gauge sending unit mounted in the stock gauge sending unit location, that the two stock temperature sending units (gauge and PCM) will read temps as much as 60 degrees apart while moving at high speeds on a cool night. If you stop and let the car idle long enough, eventually the radiator coolant temperature equals what the actual coolant temp in the block is, and both readings are relatively the same. As soon as you start moving, the temperature read at the gauge sending unit will drop rapidly, however the actual engine temperature, and that which is sensed by the PCM sending unit, remains about 10 degrees above the thermostat setting.

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9C1 Trunk Mat

Q: Is there something I can use so I don't mess up my trunk or my rear quarters from stuff sliding in the trunk?

A: This is option B48: "Mat, Heavy Duty Rubber Trunk (SEO)". This is a heavy rubber mat factory cut to fit the trunk floor, and is an option on Caprice police package vehicles. Install it to protect the carpet and for further sound isolation. You can also install 1" thick foam padding behind the carpet on either side of the trunk, which eliminates "out-dings" from objects careening around in the trunk during high G-force maneuvers.

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Steering Wheel Radio Controls

Q: Is there any way I can add steering wheel controls for my radio, like some other GM cars?

A: Yes! You do need to replace the steering wheel, though. These controls are found in '95 and up Pontiac Trans Ams (and some other Pontiacs as well). You can also find them in late-model Monte Carlos. The Pontiac wheel is Graphite in color, as are the controls, while the Monte wheel is black, and features black controls.

There have been two different types of Steering Wheel Control (SWC) systems in GM vehicles. The first was an optical system that was used mostly on vehicles without airbags. This system used an optical coupling ring in the steering column and sent data to the radio. The newer system is analog in nature and uses the air bag coil in the column to pass a voltage to the radio. In each system the connection to the radio is only a single wire.

The analog SWC switches are just momentary contact switches wired in parallel such that when any one switch is pressed, a series circuit with a specified resistance value is completed between a hot in ACC/RUN ignition source and the SWC terminal on the radio.

For those of you who wish to install this type of steering wheel, bolting on the wheel itself on is very straight forward, it goes on exactly like the stock wheel. You need a new SIR coil from the '95 and up F-car: the SWC system plugs into the new SIR coil. The SIR coil then has a wire that runs to the base of the steering column. To wire up the radio controls you will have to connect the wires in the 4-pin connector at the end of the coil harness to:

These signals are not necessarily connected in this order, and if you want a factory looking job you will need to purchase the mating connector for both the SIR coil and the radio.

The '95-'96 Impala radios have the analog SWC feature built-in, all that is needed is to connect the switches to the SWC terminal on the radio for it to work. The switches work by connecting a pull-up resistance value between a voltage source and the SWC terminal on the radio. By reading the voltage present on the SWC terminal the radio can be made to change stations, volume, etc. The switches and resistance values are as follows:

SCV Stereo SWC Functions
Switch Function Resistance
SW1 RH Volume UP 1270 ohms
SW2 R Volume DOWN 294 ohms
SW3 R Play 348 ohms
SW4 R Mute 475 ohms
SW5 L Seek UP 715 ohms
SW6 L Seek DOWN 1180 ohms
SW7 L AM/FM 2370 ohms
SW8 L Preset 6980 ohms

Using this information one could build a control switch. All of the 8 switches should be wired in parallel with each other, such that when any one of them is pressed, it will complete a series circuit with the specified resistance level between the ignition voltage source (12v) and the SWC terminal on the radio.

If you want to purchase the switches from GM, the part numbers for graphite versions of the switch pods as used in the Firebird are 16191162 (LH Switch pod, $88), and 16191172 (RH Switch pod, $88).

The switches plug into connector C3 pin 14 on the back of the radio. The radio connector is a multi-part connector. The C3 portion is the lower part and also contains the SCV terminal I believe. The C3 portion actually clips to the other C1 and C2 connector parts, forming a larger integrated connector which plugs into the radio.

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Rear Windows Falling Off Track

Q: My rear windows keep falling off of the track. What's wrong?

A: What comes stock on the Impala is a plastic piece that goes in the window channel and has a recepticle for the ball on the end of the lifting arm. The main feature of this plastic piece is that it is designed to break if tremendous pressure (i.e. human arm caught in the window and switch activated) was put on where the lifting arm ball snapped into the plastic piece. It is shaped oblong, and is about 1 1/4" long with rounded ends. If the window sticks, this piece probably will break, and then the window will fall off of the track.

If your windows have come off track before, you have probably broken this piece, and you are now only able to roll your rear windows up by putting the metal ball at the end of the lifting arm into the window channel. This works fine to get the window up and keep them there but it is by no means a final soloution as the window channel opening is about 5/8" wide and the ball at the end of the lifting arm is about 1/4". So when the window is all the way down, the metal ball on the lifting arm usually pops out or pops out when you hit a bump. This usually results in the metal ball at the end of the lifting arm scratching your tint as the window falls down crooked into the door.

There are a total of three of these plastic pieces in each door. Two are in the window channel (one for each lifting arm) and one is in a channel (or track) that is attatched to the inside door skin and is used to adjust the geometry of the lifting arms.

When GM parts looked up the plastic part, what came was a perfectly circular plastic piece that looked like a donut (hole in the middle for the metal ball of the lifting arm). It doesn't look like it would work but it fits in the channel OK and, with a little grease and a pair of vice grips, it pops onto the metal ball also. The part number for this plastic piece is 9666748 BEARING, $2.99.

This part looks like it is NOT designed to break under heavy pressure like the old ones It is perfectly circular and not oblong, so it slides better in the channel than the stock piece. Also, this perfectly round piece comes standard on newer GM models, Impalas specifically.

BTW, if the safety break pops and you roll the window all the way down, you risk shattering the window with the scissor mechanism as it will ride out of the track and up against the window as it comes down into the well.

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Intermittent Wiper / Washer Failures

Q: Sometimes the windshield washer and wipers work, and sometimes they don't. Often I find blown fuses. What could be wrong?

A: When you use the tilt wheel, it moves a bundle of wires up and down along the bottom of the column. There is a plastic wire protector right under the wires to act as a shield and a sort of channel to allow their free movement. Right where this bundle of wires exits the channel, some of them were rubbing on a portion of the steering column or other objects nearby, wearing off the insulation and causing a short circuit.

To fix this problem, all you need is some electrical tape and a few wire ties. Lay down with your back on the floorpan and your head under the steering column and move the tilt wheel to see where the wires are chafing. Use the tape to wrap any wires that have had their insulation worn off. Then use the wire ties to bundle up the wires such that they do not contact the column or other objects while the steering wheel is tilted fully up or down. This will solve the problem and prevent it from recurring. There is no TSB on this problem, but there should be!

BTW, another area of wire chafing is the trunk light. The wires often become pinched or chafed near the LH decklid support arm, where the mercury switch is located. These wires will break or short, if they break the trunk light simply will not work, but if they break and one of the wire ends touches the body, it will create a short that can keep the light on and kill your battery.

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Caprice Wooden Door Panel Inserts

Q: Can I fit the standard Caprice wood grain kit to the Impala?

A: Yes, it can be replaced by rewelding a few parts and bolting on some other, although it's rather pricey. The doors are fairly easy to do: the dash will require a lot more work and money to complete. Mitch Posner graciously provided the parts list and installation details. Here's what you'll need for the doors:

The panels consist of two separate pieces that are attached together: you can tell from your own panels there is a separate cutout. You need four of the same parts (16671169) for all the doors (they are reversible!). Here is the complete list to get from GM, with current prices listed:

These panels are superior to the stick on woodgrain kits that cost just as much and can peel off! The dash panel, which is the only other part to complete the job, is far bigger than it looks to replace and pay for.

Note that the door welds that hold the door bezels cannot easily be undone without removing the entire door panel and unwelding (melting) the welds that attach them to an inner door panel. This is around $100 in GM labor per panel to remove and replace the panels if you don't DIY. The door switch bezels (around the lock/unlock and door levers) do in fact snap into place.

The front door armrest switch panel design is black with a woodgrain edge that may not look as good as the original all grey one. Pictures of the way all of this looks can be found at Ken Pauley's web site.

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-- Transmission and Differential --

Brake Transmission Shift Interlock

Q: How can I disable the brake / transmission shift interlock?

A: This "feature" was added to most GM cars during the time when Audi was suffering lawsuits from "unintended acceleration" cases. It prevents the driver from putting the car into gear without the brake fully engaged. It is easily defeated for more careful drivers.

For a '96, just remove the shift handle, lift off the cover plate, and unplug the connector from the BTSI solenoid. Then get some 1,1,1 Trichloroethane solvent and wipe off the white "Press Brake to Shift From Park" lettering from the console cover plate and reinstall. Other solvents will work to remove the lettering, but test them on the back side to be sure they don't melt the plastic.

On a '94-'95 the BTSI solenoid is at the base of the steering column: just unplug it. If you want to remove the white lettering, it's on the instrument cluster which is a little harder to get to but it can be removed just the same.

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Torque Converters

Q: What will a a torque converter change do for the Impala?

A: Changing to a higher stall torque converter allows the engine to rev to its powerband faster, and to stay there while accelerating. Since all street converters for the Impala still lock up, there is no difference in cruise RPM's. GM offers torque converters of several different stall speeds for the 4L60E, 4L60, and 700-R4 transmissions.

The stock Impala converter is rated to stall at 1397 RPM (actual stall will be anywhere from 1400 to 1600, depending on engine torque output), while the highest stall converter GM offers is rated to stall at 2025 rpm (actual stall will be around 2000 to 2200 rpm, depending on engine torque output). The higher stall speed means greater torque multiplication which improves acceleration off the line. This also virtually eliminates the annoying creep while idling in drive as well as the clunk you sometimes get when shifting from park into either drive or reverse.

You can tell which converter you have by a 4-digit alpha code found on a sticker attached to the converter.

The code is interpreted as follows:

Going to the S10 converter increases stall speed by 628 rpm, which feels very good indeed. The factory 2025 rpm converter is an excellent, low cost upgrade that offers a very noticeable effect on performance without being too radical.

One area that some of the better (and more expensive) high stall aftermarket converters will excel in is durability in high HP applications. While the stock converter can live behind 300 to 350 HP with few problems, going to 400 HP or more can be pushing it. Actually in my experiences the trans will go before the converter, unfortunately when the trans goes the debris usually takes the converter with it (of course the opposite is also true).

Originally, the '85-'86 Corvette torque converter was recommended as an Impala upgrade. As you can see from the 2nd digit code this is a K-140 converter, which is the highest stall factory converter available for the 700-R4, 4L60, and 4L60E transmissions. The original part number for the '85-'86 'vette converter was #8650919, which was later changed to #24201203. GM only sells torque converters as what are called remanufactured units, but depending on the converter application you order, you may actually get a new converter instead of a rebuilt unit. Unfortunately since the '85-'86 'vette is an older application, you will almost certainly get a rebuilt converter if you order under that part number. Not only will the converter be used (rebuilt), but since then some of the internal components have been upgraded.

To get the high stall converter in an updated form with the latest design, order a similar K-140 high stall converter from a 1995+ 4.3L (RPO L35) S10 Truck V6 application (p/n 24202310). This new converter uses the same basic internal components (stators, etc.) as the 'vette converter, and as such has the same high stall speed rating (2nd digit code "B").

GM ranks converters by what they call a "K-factor", which indicates torque capacity and the resultant stall speed. Mark McPhail of GM Motorsports says both the '95 L35 Truck and the '85 Corvette converter described here have the same K-140 internals, resulting in the same stall speed given the same engine torque output. Since stall speed varies with engine torque, GM gives a rating of 2025 rpm, however this converter stalls at around 2200 rpm in a stock Impala.

The L35 Truck converter is listed under a new part number for 1995 and newer applications, so you are much more likely to get a brand new one when you order it instead of a remanufactured unit. The second thing is that the L35 truck converter has damping springs added to the TCC (Torque Converter Clutch) assembly. That may explain the code difference in the third digit. This does not affect performance per se, but apparently reduces noise and possible shudder or vibration when the TCC engages. Note that although the 4th digit code is different in the S10 and 'vette converters from the stock Impala converter (code "F" vs. "G"), the lug shape and mounting pattern is identical,

Finally, this new converter costs exactly the same as the 'vette converter. Both list for about $209.66, and sell for $157.25 trade price. The stall speed is 628 rpm higher than stock but is not in anyway too high for even a completely stock Impala. Remember this is a factory 298mm (11.73") torque converter with a TCC (Torque Converter Clutch) and is a direct replacement for the factory unit. Note there is an additional $35 core charge which you will get back when you return your stock converter to the dealer.

Another company, Precision Industries, is offering a 9.5" 2500 stall converter for the 4L60E transmission called the "Vigilante". This converter, along with the Trans-Go shift kit, are supposed to be able to shave almost half a second off the quarter mile time! Be aware that the 9.5" converter will generate more heat than the stock converter, but the exceptional cooling capacity of the transmission will probably handle it. The Vigilante goes for around $800.

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Differential Gasket Warning

Q: Is there some sort of problem with the rear axle bearings and/or the differential cover gasket?

A: If you look at the rear differential cover, you will notice two small indentations on either side directly in line with the axle tubes. These indentations are to direct the flow of oil through two holes in the differential case which then flows down the axle tubes to lubricate the axles and the outer axle bearings. The differential cover gasket is also supposed to have two holes in it, which line up with the holes in the case as well as the indentations to allow oil to flow down the axle tubes.

Starting in the 1990 model year, GM has been improperly installing differential cover gaskets THAT DO NOT HAVE THE LUBRICATING HOLES!!! If you do not change this gasket to one that has the proper holes, your outer axle bearings, as well as the axles themselves, will be destroyed by around 70K miles. The damaged (under lubricated) bearings will wear grooves in the axle shafts, requiring that they also be replaced. If this is left unchecked, the metal bits from the damaged outer bearings and axles will also damage the inner bearings, pinion bearings, as well as cause the spider gears to wear into the differential carrier.

GM has been made aware of this problem, but currently has done nothing about it, and even new vehicles still come with the improper gaskets. I just purchased a new factory replacement gasket over the counter and it also lacks the lubricating holes! The village of Schaumburg now replaces all factory gaskets with a replacement Fel-Pro gasket (P/N RDS 55028-1 which does have the proper lubricating holes) at the first vehicle service or by no later than 3K miles. Since they have been doing this, they have had no problems with damaged axle bearings and axle shafts, or other excessive wear in these areas.

Be aware that GM does not acknowledge that the rear axle gasket has a problem, and that the technician will not have any idea what you are talking about if you tell him to "just fix it". You must get the gasket yourself and take it in to them (or do it yourself) to get the correct gasket. There is no TSB or recall for this gasket.

As a side note, GM full-size light-duty pickups also suffer from this problem!

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Grinding Sounds from the Differential

Q: Why is my rear differential making the grinding noise?

A: There are several possible problems with the rear axle. One is that the improper gasket has been used, which does not allow enough lubricating oil to the side outer (wheel) bearings. The rear axle gasket must be changed immediately to the proper Fel-Pro RDS 55028-1 which has the correct lubricating holes allowing more oil to flow into the axle tubes.

The second problem is that the axle manufacturer (American Axle), seems to be somewhat sloppy with respect to shim selection. When the axle is assembled, a shim is installed under one of the pinion bearings to set the pinion depth of engagement with the ring gear. Several people who have had rear gear changes indicate that the factory gears were shimmed improperly.

This points out the need to use the pinion depth gauge to determine the proper shim required if you ever have the ring and pinion gears changed. Most shops will simply re-use the existing shims, thinking that they must have been correct when the axle was manufactured. If you do ever change the rear axle gears, make sure that the shop has the proper pinion depth gauge tool, and that they USE it!

If you have noises in slow, tight turns, this is likely from the limited slip differential portion, and can often be corrected by adding two bottles of the GM limited slip additive. Even if you use synthetic you must use at least one bottl e of the additive. Also remember to change the to the proper Fel-Pre gasket immediately to the proper type, or bearing damage and excessive wear may result.

Another reason several people have been having problems with their rear end making noises is by using synthetic gear oil. For some reason, this stuff ( even the stuff that claims it is "limited slip friendly") doesn't seem to work well with the Impala. If used synthetics and experience noises, try switching back to regular GM lube and one bottle of the additive to see if it fixes it.

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Rear Axle Gear Ratio Changes

Q: What's involved in changing the rear gears on the Impala SS?

A: Basically, you will need to change the gears, get the PCM reprogrammed for them, and change the ABS reluctor. For 3.42's and steeper, you can use GM reluctors for the B-bodies. For 3.73s and lower, you'll need an aftermark et shop like Evergreen Performance or Ligenfelter, or you can get P/N 26018946 (about $7.00) which is the reluctor used on the '91-'92 Cadillac D-body (Fleetwood Brougham) with the V4P 7,000 lb. trailer towing package. You'll also need to have either the Goodwrench staff reprogram your PCM (which they seem to be unwilling or unsure of how to do) or purchase a new PCM program that allows you to change this. The Hypertech device lets you change it dynamically.

If you are looking for something larger than a 3.73, the small block equipped light duty 2500 series trucks have a 8.5" diameter 10 bolt ring gear and are available with the 4.10 ratio. Before the introduction of the Vortec engines in the C/K truck line, the 8.5" 4.10 ratio had slightly greater availability. So you might check for pre '95 model year applications. In addition, the GM Astro/Safari twins also use an 8.5" 10 bolt rear end and had a 4.10 ratio available a number of years ago (late '80s), although they may not have had ABS at that time.

A gear swap would go for about 5 hours of time at the dealer, so you would have to base it on what they charge for an hour. Here are the minimum parts needed for the GU6 3.42 gear swap:

Required Gear Swap Parts
Item/Description P/N Cost
GU6 factory 3.42 gear set 26041514 $273 .24
20-tooth ABS reluctor #26018945 $7.4 5
pinion seal #26033578 $9.0 7
cover gasket Fel-Pro RDS 55028-1 $4.7 5
2 qts. of diff. fluid ??? $6.9 9
GM limited slip additive #1052358 $4.2 8

Since you have to press on the pinion bearings, it is recommended that you install new ones, rather than trying to press off the old ones and then press them back on the new pinion. You may also need carrier side bearings. Check out everything, and if there are problems, replace the necessary additional parts.

The axle side bearings are normally fine, it is a good idea to replace the seals. Also purchase an additional pinion crush collar, since they are useable only once, and although the gear kit includes one, having a spare will be useful if you accidentally over torque the pinion nut. Also recommended is a new pinion nut, as they are a prevailing torque (crushed) type fastener, which can loosen if used too many times.

Finally, shims are used to set the pinion depth and backlash, but you won't know which shims to get until you take it apart to measure everything. Some people will just re-use the original shims, but many people have seen that the original shims are not always fully correct. Use the proper pinion depth gauge to check both depth and backlash, and compensate appropriately with the proper shims. There are 4 different shim kits for pinion depth, and 11 kits for setting backlash.

Here are the additional parts needed for a complete job:

Optional (but recommended) Gear Swap Parts
Item/Description P/N Cost
Pinion front bearing #9418356 $35. 17
Pinion rear bearing #9413427 $34. 55
Pinion Nut #1260823 $2.3 4
Pinion spacer (crush collar) #1234726 $2.4 9
Axle seals (2 reqd) #554631 $11. 96
Shim Kits (as needed) ??? $18 each

As far as figuring out new RPM versus shift points, use the following formulas:

rpm = ((d*26.7) / ((a*b/500 + c*2.54) * 3.14/100)) * e * f


a = tire width in mm (for instance 245)
b = tire aspect ratio (for instance 50 on a 245/50-16 tire)
c = rim diameter (for instance 16)
d = speed in mph
e = rear end gears.
f = transmission gear ratio

So, for example, what rpm will a stock 94 Impala turn at 75 MPH?

a = 255, b = 50, c = 17, d = 75, e = 3.08, f = 0.70

rpm = ((d*26.7) / ((a*b/500 + c*2.54) * 3.14/100)) * e * f
rpm = ((75*26.7) / ((255*50/500 + 17*2.54) * 3.14/100)) * 3.08 * 0.7
rpm = (2002.5) / ((25.5 + 43.18) * .0314) * 2.156
rpm = (2002.5 / 2.156) * 2.156
rpm = 2002.5

Also, as a side note, the Richmond gear sets (and probably other aftermarket sets as well), do not work with the Impala SS reluctor setup. The price o f the Richmond gears is very attractive, about $200 vs about $350 for the GM's. The Richmond gears themselves will work on the Impala, but your ABS light will turn on and the ABS will not function. Until Richmond redesigns the pinion to accept the reluctor, like the GM gears, they rate as a "NO Buy". FYI, the "reluctor" on the Impala is pressed on to the pinio n shaft, which turns at driveshaft speed . It is the device that generates the pulse signal to the ABS computer for your rear wheel speed. When you change gear ratios you must also change to a reluctor with the correct tooth count . Your front wheels have their own reluctors, for a total 3 reluctors on the Impala. F-Bodies and Vettes have four reluctors, one for each wheel, and they are able to use the aftermarket gears because the reluctors are not attached to the pinion gears. And since they are not, they do not have to be changed to compensate for a new gear ratio. Simply put, driveshaft speed is altered with gear change, wheel speed remains constant with a gear change.

A very good price on Motive (what GM sources for the stock gears) can be had through Internet Racers Supply. They sell the entire kit for around $200. This compares very well to the $500+ you'll spend at the dealer.

Here's a table to give you an idea of the RPM's you'll be turning at various RPM's with the more common gear sets. Note that these tables are provided for rough comparison purposes only: drivetrain losses and tire size differences may cause variations from these numbers.

MPH vs. RPM for Common Gear Rations

MPH vs. RPM for Common Gear Rations
First Gear Ratio (3.07:1)
RPM MPH w/3.08 MPH w/3.42 MPH w/3.73
500 4.26 3.84 3.52
1000 8.53 7.68 7.04
1500 12.79 11.52 10.5 6
2000 17.05 15.36 14.0 8
2500 21.32 19.20 17.6 0
3000 25.58 23.04 21.1 2
3500 29.84 26.87 24.6 4
4000 34.10 30.71 28.1 6
4500 38.37 34.55 31.6 8
5000 42.63 38.39 35.2 0
5500 46.89 42.23 38.7 2
6000 51.16 46.07 42.2 4

Second Gear Ratio (1.63:1)
RPM MPH w/3.08 MPH w/3.42 MPH w/3.73
500 8.00 7.21 6.61
1000 16.01 14.41 13.2 2
1500 24.01 21.62 19.8 3
2000 32.01 28.83 26.4 3
2500 40.02 36.04 33.0 4
3000 48.02 43.24 39.6 5
3500 56.02 50.45 46.2 6
4000 64.02 57.66 52.8 7
4500 72.03 64.87 59.4 8
5000 80.03 72.07 66.0 8
5500 88.03 79.28 72.6 9
6000 96.04 86.49 79.3 0

Third Gear Ratio (1.00:1)
RPM MPH w/3.08 MPH w/3.42 MPH w/3.73
500 13.04 11.75 10.7 7
1000 26.09 23.50 21.5 4
1500 39.13 35.24 32.3 2
2000 52.18 46.99 43.0 9
2500 65.22 58.74 53.8 6
3000 78.27 70.49 64.6 3
3500 91.31 82.24 75.4 0
4000 104.36 93.98 86.1 7
4500 117.40 105.73 96.9 5
5000 130.45 117.48 107. 72
5500 143.49 129.23 118. 49
6000 156.54 140.98 129. 26

Fourth Gear Ratio (0.70:1)
RPM MPH w/3.08 MPH w/3.42 MPH w/3.73
500 18.64 16.78 15.3 9
1000 37.27 33.57 30.7 8
1500 55.91 50.35 46.1 6
2000 74.54 67.13 61.5 5
2500 93.18 83.92 76.9 4
3000 111.81 100.70 92.3 3
3500 130.45 117.48 107. 72
4000 149.09 134.26 123. 11
4500 167.72 151.05 138. 49
5000 186.36 167.83 153. 88
5500 204.99 184.61 169. 27
6000 223.63 201.40 184. 66

Back to the index...

Transmission Leaks

Q: My transmission is leaking something. Any ideas?

A: GM has a TSB out for 95-96 Impalas that explains leaks from around the front of the tranny. It appears that the front pump bushing may be causing the problem. This applies to all 95's and to 96's with tranny's built before September 11 (Julian 254). The pump bushing is spinning and walking out of the body. The bushing is removed and replaced with a revised one.

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Common Transmission Problems

Q: Are there any common transmission problems I should watch out for?

A: Most owners report a transmission "clunk" when letting off of the throttle just as the tranny does a 1-2 shift. Most dealers call this normal.

TSB 67-71-47 describes a 3-2 part throttle downshift flare (replace 3-2 solenoid). Some owners with 4L60-E trans built before May 24, 1996/ Julian date 6145 may experience an engine speed flare of 1000-2000 RPM, during a part throttle downshift at 19-31 mph. This condition will not set any DTC's. This is caused by an exhaust seat on the 3-2 control solenoid backing out. This is for the 1996 models only and applies to everything using the 4L60-E, not just the Impala.

The sprag unit is a weak link in the tranny. When it goes the clutches start to slip and they burn out. Further wear overheats the converter and Experience and what several transmission shops have shown this to be the case. Raybestos has just introduced a new Sprag unit called the Mechanical Diode. The unit was developed after many 4L60E failures from Police and Taxi company complaints.

The unit was developed using an Impala SS. The Impala is owned by Frank Slocum, President of Raybestos aftermarket products. This product was developed for High Performance Vehicles. The Mechanical diode can handle 1400 ft. pounds of torque, twice the output of two (2) big block 454's. Also in the brochure it shows the high end limit at 2510 ft. pounds

Raybestos also offers other products to make your tranny "bullet proof": TCI special built 12" 2800 stall converter with anti ballooning plates, a Raybestos Keylar band, Raybestos Blue Plate clutches, and Lube Guard, a special Transmission additive. They also offer an aluminum transmission pan that has heat fins to cool the fluid down by about another 30 degrees.

If you are interested in contacting Raybestos, call Charlie Browning at 317-364-4560 for further information. Charlie can send you information and a list if their distributors. The part number for the Sprag unit is MD700-R4 and is currently the only model available.

Another problem relates to overheating of the transmission if run in lockup mode at high speeds. In lockup mode, some of the transmission oil is not routed through the cooler, but is dumped straight back into the pan. This was done to increase fuel mileage. TCI and Art Carr both replace the converter clutch valve to direct all fluid through the cooler. This will increase flow from aabout 1 gallon per minute to 2 gpm. TCI recommends doing this even to a stock configuration, as it dramatically increases reliability.

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Rear Axle Ratios

Q: What rear-end ratios are available in the Impala / Caprice?


Impala And Caprice Available Rear Gear Ratios
Axle Ratio RPO Code Ring/Pinion Teeth Application
2.56 GM8 41/16 Std. Roadmaster LT1, 93+ Fleetwoods.
2.73 GU2 41/15 Std. Caprice L99 (exc. 9C1)
2.93 GW9/GU3 41/14 Std. Caprice LT1 (exc. 9C1) and 93+ Fleetwood Broughams, Opt. Roadmaster LT1
3.08 GU4 40/13 Std. Caprice 9C1/LT1 (Police), Std. Impala SS
3.23 GU5 42/13 Opt. Caprice L99, Std. Caprice 9C1/L99 (Police)
3.42 GU6 41/12 Std. 91-93 Caprice 9C1/L05, Std. 94+ Fleetwood w/V4P
3.73 GT4 41/11 Std. 91-92 Brougham w/V4P

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Second Gear Start

Q: The owners and service manuals say that the Impala should start in second gear while in the "2" position, but mine doesn't. The service department says they all act that way. What's the deal?

A: All '94's and some early '95s came with the second gear start function built in. This has been verified. Sometime early in the '95 production run, a new PCM calibration was issued that either disabled the 2nd gear start feature on accident or on purpose. Some have heard that it was because too many people where blowing transmissions by starting in 2nd with a trailer attached.

Chevrolet is aware of this problem and has opened a file folder on it (number 960149175). Call 1-800-222-1020 for the latest scoop on the problem. Some list members are actively working to get this problem resolved as of March, 1996. Try calling Jeremy at extension 5138 for more information on the problem.

Several of the aftermarket PCM reprogrammers can offer this feature on their programs.

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Shift Kits

Q: Can I improve the transmission to make shifts "tighter" and shift with more performance oriented up/down shifts?

A: Since the PCM has a lot of control over the transmission feel and shift points, most of the performance PCM programs reprogram the transmission for a better shifts. Changes include harder shifts, increased rev limits, delayed upshifts, and quicker downshifts.

Another member has suggested using Type F transmission fluid instead of the Dexron stuff. Dexron is formulated with more "slip" agents in it, resulting in sloppier shifts. This comes from its origins in the land yachts of the seventies.

Also, Scott Mueller posted the following data on a couple of shift kits that are available for the 4L60E in the Impala (and many other GM vehicles):

I have purchased both the TransGo (818-443-4953) and Art Carr (714-962-6655) shift kits for the 4L60E. I must say I was blown away by the TransGo kit, it is extremely comprehensive and well thought out. The Art Carr kit is very simple by comparison.

The Art Carr kit (#17050) for the 4L60E costs $59.00 wholesale. It includes nothing more than a 3-4 accumulator spring, an orifice plug, two washers and a cotter pin! The instructions are vague and consist of only one sheet of paper. They do throw in a new filter, but include a crude cork pan gasket instead of the much improved composite type pan gasket the factory uses.

The TransGo kit cost $88.57 (wholesale) and includes about 10 times more parts, including accumulator springs, pressure valve springs, servo springs, check balls, a re-designed 1-2 shift valve, boost valve, new servo o-rings, and more. The documentation is excellent, and this even includes a very cool installation video which shows exactly how to install the kit step by step (on a brand new '95 Impala SS no less! ). The video is so well done that anybody could easily install this kit, even though it is far more comprehensive and complicated than the Art Carr kit.

In addition to firming up the shifts, the TransGo kit also allows the transmission to hold any gear you select to any speed, and allows downshifting instantly on command. It even contains a mod that shortens the reverse delay and release time, which is very long on these transmissions. Also, there are several optional or adjustable features in the TransGo kit, which means even after you install it, you can easily re-calibrate it for harder or softer shifts.

The TransGo kit does not include a new filter like the Art Carr kit, but does include the proper factory style composite pan gasket. A factory filter and gasket kit costs $15. TransGo has been in the transmission rebuilding and shift kit business for quite a bit longer (over 35 years) than Art Carr, or anybody else for that matter.

Below are some tips for installing the TransGo kit from NAISSO member Tom Pierce. The September 1996 Car Craft Magazine has an article on doing this modification to a 1996 Impala SS if you'd like to see how it's done before you buy the kit.

The car now shifts like it MEANS it, and even medium throttle shifts are quick and crisp. Curiously, I can't tell much of a difference in the downshifts after installing the kit, but upshifts are killer!

Here are some additional tips from Steve Das:

During the installation of the shift kit, there are spring and washer selections that are to be made that affect particularly the 1-2 shift firmness. In step 1, the shift kit was installed with the stock or original "1-2 shift firmness" spring which is specified for "HD, police, taxis" use instead of the white spring (specified for High Performance) supplied in the kit. In addition, I used only ONE washer in the 2nd accumulator. I noticed that the video showed washers with LARGE holes in them that would easily fit over the pin boss and into the bottom of the accumulator. The washers supplied with my kit had small holes in them: just large enough to fit over the pin. Since there is a boss extending above the spring seat, this kept the washer from bottoming out and in fact, results in probably about as much compression as two large hole washers would. The shifting now is nice and firm in all gears and will BARELY break the tires loose on the 1-2 on rough concrete freeway surfacing at full throttle which is the way I wanted it. I have ridden in a car that used the white spring and two washers and is much harsher shifting than this. In fact, it will READILY break the skins loose on ANY surface at full throttle.

Getting the large external cover off of the 2nd and 4th piston assembly is a job! The passenger side catalytic converter MUST be moved (remove the nuts, drop the converter down a little, pivot it to the outside, push one of the bolt holes back up over one of the studs and install one of the nuts hand tight). The converter will then hang out of the way and you do not need to unplug the O2 sensor wires.... which is not easy to do! In addition, the converter heat shield must be removed. I had to actually bend the bracket for the heat shield that is next to the piston cover to get the cover off. In addition, after disassembling the piston assembly per the instructions and installing the two gold washers, it was IMPOSSIBLE to get the snap ring back on the 2nd piston retainer without the use of a press to compress the springs enough to get the large snap ring back in. Also, I found that several of the holes you have to drill in the separator plate are VERY close to their original size. Don't be surprised. In addition, it would appear that the aluminum plug that you put into the separator plate with a hammer blow or two, is too small; it isn't. It will work fine. Don't forget to drill the hole in it after installing it in the plate. Remember , the pressure regulator that goes into the bottom of the pump has TWO snap ring groves. Use the top one as explained in the video.

After the work is completed, the video says to add 6 quarts of fluid and start the engine, then immediately add two more quarts. Apparently, some of the 4L60E transmissions hold more fluid after pan and valve body removal than my '95 as this results in about two quarts too much fluid! I would suggest adding FIVE quarts or a little less, starting the engine and checking the level. If you do get it too full, there is one of the transmission oil cooler hoses at the lower radiator fitting that has a spring clamp on it. Remove the spring clamp, pull off the hose and put another hose on the exposed nipple. Put this hose in a drain pan and start the engine. The fluid comes from the added hose and into the drain pan. Then you can reconnect the hose and replentish the fluid back to the correct level. Incidentally, on most GM transmissions, this is a good way to drain the torque converter after a filter change. I have not looked at the fluid flow for the 4L60E but assuming it is the same as most, the fluid from the convertor is sent through the cooler and then to the pan. Fill the transmission with fluid (I usually add about two quarts too much in this case) and run the engine until the fluid coming from this hose is clean. Don't let the trans run out of fluid but usually you will see the color change after about 6 quarts has been pumped out. You have then drained the converter of the old fluid and replaced it with clean fluid from the pan.

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Torque Converter Clutch Lockup

Q: My torque converter seems to lock up sooner than my buddies. What's the difference?

A: Ken Rolt & Robert Acorcy report the following:

The year (94 to 96), or model (Impala, 9C1, LT1 equipped Caprice) makes no difference in the lockup speed. It was whether you had the Chuggle & Surge TSB update.

WithOUT the TSB update - 3rd gear lockup ~37 mph; 4th gear lockup ~ 46 mph.

With the TSB update - 3rd gear lockup ~43 mph; 4th gear lockup ~ 53 mph.

All the above numbers are +/- 2 mph in range, and are accounted for by either speedometer error, or error in reading the speedometer.

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-- Body and Exterior --

Amber / Parking Light DRLs

Q: I see some of the new vehicles from GM have super-bright parking / turn signal lights instead of using the headlights as DRLs. Is there anything I can do like this on the Impala?

A: Those lights actually use 2057 bulbs, which are dimmer both on low and high filaments than 2357s. The difference is that on the '97 F-cars they wire the turn signals to work as DRLs (not the parking lights), which means that the 32 candlepower bright filament stays on all the time. When you use the turn signal, those applications switch the brighter filament OFF rather than ON. In otherwords, if you installed the brighter 2357 bulbs in the F-cars, the DRLs would be even brighter, since they would be using a 40 cp filament instead of the 32 cp filament they use stock.

You could get the same effect on an Impala if you wire the turn signal/park lamps so the brighter filament comes on with the parking lights. Also you would have to rewire the relay so that it flashes the filament off rather than on when the turn signal is used, just like in the F-cars. Then when you turn on the park lamps, you'd have the bright DRL style amber lights lit up just like on the '97 F-cars. That would also give you a "switchable" DRL, that is by using the parking lights you could turn them on. You could also wire it up to come on all the time the car is running. This would be an excellent use for the top Caprice wagon switch added to the LH side of the dash!

If you have to have DRLs, the use of the turn signals would be preferable to the reduced power high beam headlights. They use less power, run up the hours on cheaper bulbs, are much less offensive to traffic in front of you, plus they look better and more distinctive as well.

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Replacement Bulbs

Q: What replacement bulbs are needed for the various auxiliary lamps on the Impala (e.g. backup, CHMSL, parking)?

A: What follows is Scott Mueller's dissertation on the subject:

The factory installs the following bulbs for the following applications:

What is interesting is that although there are several different numbers listed for the above two sets of applications, all of those listed above comprise basically two different kinds of bulbs! All of the bulbs in the first group plug into exactly the same socket and have exactly the same dimensional specifications, and likewise for the bulbs in the latter group. Many different numbered bulbs interchange in these two types of sockets. All of the bulbs in the first group, which comprise the tail and backup lamps, Center High Mounted Stop Lamp (CHMSL), front park/turn signal as well as the cornering lamps are technically classified as a type S-8 bulb with a DC (Double Contact) index (staggered pin) base, dual C-6 (straight across bar type helical coil) filaments, and a 1.250" LCL (Light Center Length is the distance from the base to the filaments). These bulbs are about 1.041" (26.44mm) maximum diameter and 2.0" (50.8mm) in overall length. There are several bulbs with these exact same specifications, however they differ in the light output or wattage of each filament, and in some cases the average filament life.

There are several bulbs which meet the S-8 specification, and which are interchangeable in an automobile application:

 Trade          Design                  Avg.
   No. Filament  Volts Watts  Amps  CP  Life
 2057       Low   14.0  6.86  0.49   2  5000
           High   12.8 26.88  2.10  32  1200  
 1034       Low   14.0  8.26  0.59   3  5000
           High   12.8 23.04  1.80  32   200
 1157       Low   14.0  8.26  0.59   3  5000
           High   12.8 26.88  2.10  32  1200
 2397       Low   14.0  6.72  0.48   2  5000
           High   12.8 28.54  2.23  40   400
 2357       Low   14.0  8.26  0.59   3  5000
           High   12.8 28.54  2.23  40   400

CP = Candle Power
This data was taken from a Wagner Lamp Specification Guide, other brand bulbs may vary slightly in specs, but not by much. As you can see from this table, the bulbs are listed roughly in order from dimmest to brightest. For example, comparing the 2057 that comes in the stock Impala taillight with an 1157 replacement, you can see that they are essentially the same bulb, except the 1157 would be 50% brighter on the low (parking light) filament.

You can install the 2357 bulbs in your taillights, backup lights, and cornering lights, which are 50% brighter on the low filament (parking lights) and also 25% brighter on the high filament as well. This will make the brake lights, turn signals, and cornering lights that much brighter. There is a slight tradeoff in bulb life, but 400 hours is the average life of a headlight bulb anyway, and brake lights and turn signals are not on continuously. Note that the super bright 2357 bulb was already factory issue in the CHMSL.

Each one of these bulbs is also available in an "NA" version, which means the bulb is coated with a Natural Amber coating. For example, the stock Impala front park/turn signal bulbs are 2057NA, but you can replace them with brighter (both in park and turn signal mode) 2357NA bulbs. Just one more thing to make your Impala stand out from the crowd.

Now for the other group of lights: the Rear Side Marker, Rear License Plate, Ashtray, Rear Roof Rail (reading lamps), Instrument cluster, and Warning/Indicator lamps all use the same basic type of bulb. These are a T3-1/4 Wedge Base bulb, which is about 0.4" (10.3mm) in diameter and 0.81" (20.6mm) in overall length. There are several bulbs which meet this specification, and as such are interchangeable:

 Trade Design                  Avg.
   No.  Volts Watts  Amps  CP  Life
   161   14.0  2.66  0.19   1  4000
   158   14.0  3.36  0.24   2  3000
   194   14.0  3.78  0.27   2  2500
   192   14.0  4.62  0.33   3  2000
   168   14.0  4.90  0.35   3  1500

The instrument cluster uses a variation of the wedge bulb. They are mounted in a twist lock base that plugs directly into the printed circuit board on the back of the cluster. When sold with the base, these are called PCxxx bulbs, for example a PC194 is basically a 194 bulb that comes soldered into a PC (Printed Circuit) board twist lock base. Older GM cars (around '90 and earlier) used a standard bulb which would plug into a separately available twist lock base, allowing you to easily change the bulb since you could re-use the base. The newer ones have the bulb permanently soldered into the base, so when one burns out you have to try and find the special PCxxx version rather than just replace the bulb in the existing base.

If you are going to change your instrument cluster bulbs to brighter ones, get the separate PC wedge bulb base. Then you can use any one of the non-PC standard T3 1/4 wedge base bulbs by just plugging them in. You can get the correct stand-alone PC wedge bulb base from GM under p/n 25015169. Use that base and install a conventional 168 wedge bulb, which lights up the background numerals and needles much brighter. If you want you can also replace some of the warning indicators with brighter bulbs also, that way when they light up you can't miss them.

Do you really want to see inside your trunk? Aside from the second trunk light (P/N 1026 8235) if you really want to light it up, replace the bulb(s) with the 921's.

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Repairing Paint Chips

Q: How should I go about repairing tiny chips in the paint?


  1. Get some of the correct color touch up paint (you can get it from Goodwrench).
  2. If possible, get some touch up clearcoat.
  3. Apply a thin layer of the color coat
  4. Wait an hour or so and apply another coat
  5. Apply coats of paint until the chip is almost, but not quite, level with the normal paint surface
  6. Preferably, wait about a day, or at least an hour, if you're like me and lack patience.
  7. Apply a few thin coats of the clear (or additional color coats if you couldn't get the clearcoat) until the paint actually is a little higher than the surface.
  8. Wait a day or two for the paint to cure a bit: you really do need to wait a couple of days here!
  9. Lightly sand the chip area with a 2000 grit or 9 micron, 1" sanding disk and back-up pad (a body shop supply shop will have it) until the chip is level with the surrounding areas. Don't worry about scuffing the surrounding areas: it'll buff out.
  10. Using a lamb's wool pad and a rotary buffer, buff out the scratches using 3M Finesse-It compound, also from the body shop.
  11. If needed, and black will need it, deswirl the the area using a random orbital buffer/sander with a foam pad and a low abrasion polish, like 3M Finesse-It Final Finish.
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Cleaning, Waxing, and Drying

Q: Do you have any tips on good products to use to keep the Impala looking its best?

A: You'll usually find as many opinions as people you ask about things like that. Basically, you need to find what seems to work well for you and use it.

As far as washing, be sure to use a real car wash, and not a dish soap. Disk soap will pull wax from the car and remove oils from the paint. Use a high quality wash, such as Meguiar's or Zymol, to wash with. Remember, it is only the soap and water that is keeping all of that dirt in suspension and preventing your wash mit from acting like a piece of sandpaper.

Drying can be done many ways. One way is to use (a lot) of very soft, lint-free terrycloth towels. Diapers and cotton tee-shirts also seem to work well. Be sure they are 100% cotton, or you can scratch the finish. Another way is to use a genuine leather chamois. You can get the car dry enough with these that you won't need a towel. The downside is that they are expensive, and they are difficult to wring out and care for. A less problematic alternative, although with poorer absorbtion characteristics, is a product called The Absorber. This is a man-made chamois that can be tossed in the washer with your other towels. You need to follow behind it with a terry towel to finish off the water beads, but it soaks up a lot of the water and is really easy to wring out. Another tip: don't use any fabric softener or bleach on the towels you use on the car: use detergent only, and stay away from the dryer sheets.

As far as waxes or polishes, no one that I have talked to has ever had a problem with the Meguiars line. They have a wide variety of products and their finish seems to look great. Zymol (the expensive stuff, not the Wal-Mart stuff) also seems to work very well. Several list members have had great luck with a product called The Treatment. This is available from Andersons, Western Auto, or directly through NAISSO. This stuff supposedly works very well on black cars.

For a dark car, you might also want to invest in one of the no-wash cleaners, such as Meguiars Final Inspection spray or the like. This works great to remove little spots and things and really gives the car a deep shine when you use it.

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Color Choices

Q: What sort of color choices are avaiable on the Impala?


Color Choices for Impala SS By Year
Color Code 1994 1995 1996
Black 41 X X X
Dark Cherry Metallic 77 - X X
Dark Green-Grey Metallic 18 - X -
Granite Metallic 03 - - X
There was one car that came from the factory with a non-stock color. It was painted especially for the owner, and even had paint shipped to off-site suppliers for the bumper skirts, etc. Unfortunately, it was virtually destroyed in a hail storm.

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Daytime Running Lights

Q: Do Impalas come with DRL's, or can they be added?

A: All Canadian model Impalas come equipped with standard daytime running lights (DRLs), but no American model comes that way. However, GM does make a module that allows DRLs on American models. This module (P/N 12370131) CAN be made compatible with the Twilight Sentinel System which came as original equipment on the car.

Installation note 1 on the back of the instruction sheet details a remedy to prevent interaction with the Twilight Sentinel that results in relay chatter and flickering parking lights. It involves installing a standard automotive 5 pin SPDT relay to isolate the Twilight Sentinel output from the headlamp circuit when the Twilight Sentinel is not activated.

The only hard part was finding the Twilight Sentinel Module (I had not received my service manuals yet and the instructions don't tell you where it's at). It is located under the glove box behind the passenger kick panel.

The system works like this: Start car in daylight; 15 seconds later headlamps come on (low beam only at reduced power, no parking, tail, or dash lights); when it begins to get dark the Twilight Sentinel kicks on full power and the other lamps. Cool. If you start up in the dark, the Twilight Sentinel will have your lights turned on.

There is a small flaw in the GM fix however. It only occurs if the Twilight Sentinel turns your headlamps off and your headlamp switch is off (Mr. Goodwrench says to always have the switch on at night for added safety). If this happens the relay chatter will start. You can unlatch the new relay and stop it easily by switching to high beam and back.

If you put a sun shade in the windshield, take it out before you start the car during the day or the Twilight Sentinel will think it's dark out and will have the headlamps on when you start up. Then it will turn them off and you'll have to flash the high beams.

GM has come out with a second set of directions which may eliminate the chatter. Ask your dealer for information. The just of it is that you need to cut the big yellow wire behind the RH kickplate going to the twilight sentinal and insert an '87a' relay. This fixes the problem once and for all: be sure to get the latest directions when you pick up the kit.

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Adding Flash-To-Pass

Q: How can I implement a flash-to-pass feature on the Impala?

A: Install a dimmer switch from a '94+ Cadillac Fleetwood. This will flash the low beams when you pull the control stick back. See the technical archives for a detailed installation procedure.

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Gas Bib

Q: How can I keep gas from dripping on the rear bumper when fueling?

A: White Caprice vehicles get a special rubber "bib" that is installed behind the license plate bracket. This bib prevents fuel from dripping on the rear bumper during refueling, and is installed on white vehicles because gasoline can cause the paint to yellow. This is a worthy feature no matter what the color, and it is easy to add your Impala. P/N is 10186225, and it will be $10-$12.

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Q: How can I improve the headlamps?

A: Option T84: "Headlamps, Export, RH Rule of Road". These are export headlamp capsules that directly replace the standard US lamps. They are made of glass instead of plastic like the US versions, and have a much better light pattern including a very sharp cutoff. They also include additional "positioning" bulbs which are designed to come on with the parking lights for use in certain European cities that do not allow headlights to be used even at night. The positioning bulbs are mounted in the parabolic reflectors such that they make the reflector look as if it is lit, even though the main headlamps are off. The T84 lamps also feature H4 halogen bulbs, which you can replace with 80/100 watt versions for increased brightness. The very sharp light cutoff insures that no light is directed into oncoming vehicles, so nobody is blinded. One interesting feature of the T84 lamps is that the headlamps are moved inboard towards the grille within the glass capsule, and the turn signals are outboard, which is exactly opposite from the US spec. lamps. This gives the car a totally unique front end appearance, and the clear glass lenses add to the effect. Installation instructions can be found in the technical archives.

Another option is to mount foglights in the grill. John Green has a complete new grill that consists of two quartz foglights installed already and a center light that fills the bow tie area that when turned on glows bright red. All you have to do is remove your grill and replace it with his, hook up the wires and switch (included), and then your in business. There is a special price for NAISSO members.

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Hood Insulation

Q: My underhood insulation is looking pretty bad. What can I do to replace it, and how can I keep it nice?

A: You have to start with a brand new piece of hood insulation. Order it from your dealer, it is $64 list, $45 wholesale. Also order a bunch of the large plastic retainers as you will likely damage some when you remove your existing insulation. The hood insulation is part #10196123, and the retainer's are part #3977775, which come in a box of 25. You only need 15-16 of these. You can attempt to salvage your current insulation by using the same tool you use on your door panels to remove the clips.

First, you will have to remove the hood lamp. It is riveted on with aluminum rivets. Drill them out, but first put a piece of tape on the drill bit to act as a stop. You don't want to slam the bit all the way through and put an out-ding on top of your hood! Pick up a set of the standard black oxide 7mm hex screws with integral washers that GM uses on practically everything to re-attach the lamp. These screws fit perfectly in the existing holes and now you can more easily remove and re-install the hood light without the hassle of rivets, plus they look factory.

Next, pull out the retainers and rip off the old insulation. You don't need to preserve it so tearing is OK. Cover your engine compartment with a plastic sheet as when you rip the hood insulation, since all kinds of debris will come down, including fiberglass from the insulation itself.

Now, take your new hood insulation and lay it out on a table. Go over it with a pair of scissors to trim any unsightly edges or frayed areas. Get some good quality gloss black enamel paint, you will need several (6-8) cans. First do a light coat over the whole thing to sort of seal it, and then concentrate mainly on the side that will show. The insulation will soak up the paint like a madman, which is exactly what you want. Lay extra paint along all of the edges to really seal them up and prevent any future fraying.

Then just let it dry and install like the original preferrably using new retainers. Either screw on or rivet on the hood lamp and you are done. If you are thinking about adding a second underhood lamp, now is the time to do it. You will now have completely sealed and non-fraying hood insulation that has a deep and rich black appearance. It also does not get as dirty in the future since it is basically sealed with the paint. It is a touch that few people will ever notice directly, but it will make your engine compartment stand out from the rest!

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Alternative Horns

Q: The horn is a little wimpy. Can I beef it up?

A: Stock Impalas come with 2 horns located in the left front fender, near the air box. These play a high A note and a low F note. The Roadmaster cousin have 2 more horns in the right front fender; a high C note and a low D note. The change in sound from the basic two-tone to a four-tone blast is appreciable.

Installation is fairly straight-forward; tap into one of the wires for the stock horns and route a 12 gauge wire to the right side and connect to the new horns. Mounting brackets come with the horns (mine came with piggy-back wiring connectors, also, but some horns do not come with the wiring: make sure you get the wiring). You'll need 5/16" bolts, nuts and washers to connect the new horns.

You'll need 1 Horn, High C Note, PN 1892246 (dealer is $41.75, net is $31.31) and 1 Horn, Low D Note, PN 1892162 (dealer is $40.25, net is $30.19).

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94 Impala SS Rear Window Inserts

Q: I have an older Caprice but really like the looks of the 95-96 rear window inserts. Can I use the rear window inserts from a '94 Impala?

A: Yes! Anyone with the triangular window can buy the plastic inserts that came on the 94 Impala SS. They come in black only and with the small deer emblem on. Parts #'s are 10248296 and 10248297. Cost is about $25 each.

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Red Bow Tie

Q: What's with the red bow-ties on the some of the Impalas I see? Does this mean something special?

A: The red bow-tie has become the unoffical NAISSO identifications. If you see an Impala with a red bow-tie on the front instead of the stock silver one, you can almost bet they are a NAISSO member. The red bow-tie was also used by Jon Moss on the original Impala SS, and was the only part of the car that was not approved for production, so adding the red bow-tie really completes Jon's creating. Lastly, with the availability of the Cavalier Z24 Red Bow Tie (CRBT) and the ease of installation, it's a quick and easy modification to perform. Check the technical archives for details on how to install the red bow tie.

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Windshield Pops and Squeaks

Q: Is there any way I can prevent the windshield from squeaking and popping when I go over bumps?

A: That "popping" noise comes from the reveal molding rubbing on the windshield on the passanger side. If you pull off the soft rubber molding that lines the A-pillar, the reveal molding, which is harder plastic, is directly underneath and mounted into the pillar w/ 4-5 screws. Take off the reveal molding and place a "gasket" between the molding and the windshield. You can use a piece of plastic, like a garbage bag, to do the job. Nothing fancy is necessary because when you're finished, you won't see a thing. Just remember to re-seal the screw holes with RTV silicone for extra water protection.

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9C1 Wiper Blades

Q: What are the "9C1 Wipers" I hear about, and why are they special?

A: The police package (9C1) wipers are designed with a small "wing" in them that prevents them from lifting off of the windows at high speeds. This is a popular add-on item for the Impala. The GM part number is 10283602). Oddly, the 9C1 wipers are avalaible at a much discounted price in Canada. They can be ordered via any of the Canadian dealers for about $8.40 (cdn) each, instead of about $25 each in US.

Cory, at Dueck Chevrolet on Marine, can help with this deal. Their telephone number 604-324-7222 (call collect) or 1-800-665-8257. Mention Mike Yang's name and NAISSO, and Cory will take care of it for you.

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-- Police Package (9C1) Caprices --

Police Package Optional Equipment

Q: What sort of optional equipment can you get on the 9C1 Caprice?

Caprice 9C1 Options
RPO Code Descriptions Price
9C1 Police package $1,159
LT1 5.7L engine $325
QQG R4Y "V" Rated Goodyear P235/70R15 tires $64
6N1 Inside Driver Door Handle releases Lock $20
6C7 Auxiliary Dome Lamp $22
6J6 Rear Window (deck) Brake and Stoplamps $170
6J3 Flashing Headlamp (Wig-Wag) wiring provisions $80
T53 Alternating Flashing Trunklid Warning Lamps $225
8X3 Bilstien shocks $275
7X7 Dual Spotlamps $250

Grand Total $2,590

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Overview of the Caprice 9C1 (Police) Package

Q: What's a 9C1 option? What does it do?

A: The police package is available on the Caprice for $1159 (1994, and probably 1995, too). You get a whole slew of police-edition specific equipment, much of which also goes on the Impala. However, the Impala does not get all of the special heavy duty equipment of the police package Caprice. It's generally cheaper to get an Impala and add on the missing equipment than to get the Caprice and bring it up to Impala standards, though.

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Police Package Standard Equipment

Q: What exactly does the 9C1 (police package) option get me?

A: You get the following list:

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Buying a Used 9C1

Q: I'd like to get a used 9C1 to complement my Impala. What should I look for?

A: Most police departments and highway patrols get rid of their cars after a couple of years. The quality of these cars varies greatly: you are usually best suited looking for cars that are assigned to individual officers, as they tend to take better care of them than "pool" cars. Most states or municipalities auction them off at given intervals. You may also want to go through a broker to attempt to purchase used police vehicles to avoid the hassle and risk of the auction: you usually don't get a good chance to look over the car at auctions.

A 94-96 LT1 9C1 is the way to go, but you will pay more for the LT1 engine. If you are willing to give up 55 to 65 HP right off the bat, you can get a '91-'93 for much less than a '94 or later. The price of a given car depends mostly on year, engine, condition and mileage. Expect to pay between 5K to 15K for a '93-'96 9C1. You can find the "LT1" code on the SPID sticker inside the trunk. Also look for the "9C1" code to make sure you are getting a real police car with all of the Chevy features. The L99 4.3 engine is weaker than the older 91-93 5.7L V8s.

The '91-'93 cars have the LO3 or LO5 engines. You can check the engine type by looking at the eigth digit of the VIN.

Also note that all '91-'93 LO5 9C1 cars got 3.42 gears standard, while LO3 cars had only 2.56 gears standard and 3.08 gears optional. All '94-'96 LT1 9C1s got 3.08 gears standard, L99 9C1s got 3.23 gears standard. There were no optional gears with any LT1, L99, or LO5 9C1 cars. Unlike with the Impala, the G80 Limited Slip differential is not standard on 9C1s but was optional for all models and years. Again, check the SPID label inside the trunk.

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-- Exhaust Systems --

Aftermarket Exhaust Systems

Q: What can I do to get a more performance oriented sound from the Impala exhaust?

A: So far, there have been several setups mentioned on the list.

Borla Cat-Back Exhaust


Flowmaster Muffler Replacement


Flowmaster Cat-Back Replacement


  • Part Name/Number: Flowmaster Impala SS Cat-Back System, PN 17118
  • Construction: Aluminized Steel Tubing with Polished Stainless Tips
  • Resonators: None
  • H-Pipe: 2" H-Pipe Included
  • Diameter: 2.25"
  • Claimed HP Increase: N/A
  • Street Price: Evergreen Performance offers it for $400 for NAISSO members.
  • Comments: The tips are very much like Mustangs: they are polished stainless tips that are very visible. The tips parallel the body seam for two and a half feet starting at the rear of the wheel opening and exiting just past the bumper. Very showy, but not overpowering. When you fire it up, it sounds like a Flowmaster. No deep muted bass, but the traditional hollow trashcan crackle. They include very special mufflers they have engineered just for the Impalas: extra large, extra long, 5 inch thick case for high flow (universal Flowmasters are only 4 inches thick). They also include extra chambering for noise reduction. The kit is extremely quiet from inside the car: there is no noise at all! Punch it, and you hear it. Cruise it, and silence is all you get. There is no bad speed or resonance. Flowmasters and quiet, not synonymous until now!

    Walker Muffler Replacement


    Walker Cat-Back Replacement


    ATR Cat-Back Systems


    SLP Cat-Back System


    B&B Performance TriFlow Cat-Back System


    Muffler Delete


    Most members have found that the addition of a crossover pipe ("H" or "X", but the "H" seems more popular and Borla recommends it over the "X") smooths out power production and does a good job eliminating torque "humps" in the powerband. It is an easy install just before the muffler and should cost less than $50. Recommended for all exhausts, stock and modified. Several members have also reported that it helps with some of the exhaust drone mentioned before.

    Note that removal of the resonators is not really discussed above. Experience has shown us that removing from a stock (or modified) exhaust system doesn't really show much gain in the area of power or sound. Also, they are really just straight-through pipes, so there's not much of a flow restriction there. On the muffler delete option, they may help quiet the exhaust a little bit. One reason you may want to delete them is for driveway clearance. In this case, it makes sense to pipe the exhaust out just behind the rear wheels, ala Callaway.

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    Cracked Exhaust Manifolds

    Q: My exhaust manifold glows red hot, and I think it might be cracking. Is this a common problem?

    There is a Chevrolet TSB out for problems with cracked exhaust manifolds:

    Service Bulletin No: 67-61-19
    Date: October, 1996

    Subject: RH side exhaust manifold cracks (install a new manifold)

    Models: 1994-96 Chevrolet Caprice with 4.3L, 5.7L engines

    Condition: Some vehicles, primarily police vehicles, may exhibit a cracked exhaust manifold on the RH side of the engine.

    Cause: Thermal cycling stress due to high ambient temperatures caused by extreme driving conditions and high engine speeds.

    Correction: There are two types of exhaust manifolds used for the 1994 through 1996 model years. One manifold for the 1994 and early 1995 model years has the AIR tube screwed directly into the manifold. The other type of manifold for the late 1995 and all 1996 model years uses a male fitting in the exhaust manifold which the AIR tube attaches to.

    Parts Information: To address the exhaust manifold cracking concern for the 1994 and early 1995 vehicles install manifold p/n 12524289 and cut the metal tie bar between the number 6 and 8 exhaust ports. For the late 1995 and all 1996 vehicles install exhaust manifold p/n 12556731. These manifolds are new for 1996 and are cast without the metal tie bar. Use gasket p/n 12552469, and refer to Bulletin 47-66-03 for bolt usage.

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    Droning or Booming

    Q: Theres a droning coming from the exhaust (possibly aftermarket). What can I do?

    A: First, a crossover pipe seems to eliminate some of the drone associated with aftermarket exhaust systems. These can be welded in pretty easily in the Impala application, and can also lead to some performance increases.

    If you are using the stock exhaust system with aftermarket muffler or the muffler delete, or your exhaust tips point down on your aftermarket system, you may be able to eliminate some of the droning. Have your local muffler shop modify your system to point straight out of the back of your car, ala the Mustangs. This seems to reduce the noise by quite a bit.

    If you have been under your Impala, you will no doubt have noticed the weight hanging off of the RH exhaust flange where the converter pipe meets the intermediate pipe. The weight is actually filled with lead shot to dampen exhaust vibrations. This was added early in the '94 model year (before Impala production started) to control a resonance in the exhaust. Now there is a new bulletin which covers adding a similar weight to the LH side also to control a droning (they call it moan/boom!) in the exhaust. You may want to check to see that you have this on both sides. A technical service bulletin exists (43-66-03) so you can have this serviced if it is notice d in a stock system.

    Lastly, you may have to learn to deal with it! There seems to be an inherent drone at about 1800 RPM in these cars with any exhaust system. This is amplified more and more with the louder your exhaust is. Remember that you will have to deal with this when replacing your exhaust.

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    Q: Are there any headers available for the Impala?

    A: Arizona Speed and Marine makes an equal-length set for the Impala SS. They wrap over the valve covers and back down. They cost about $585 if you are in NAISSO and go through Evergreen Performance. TPIS also offer similar coated headers for about $650.

    Edelbrock also offers an Impala SS header. The normal price is $504.00, but you can probably get them for about $450 through club distribution channels (contact John Levitz at Evergreen Performance). Edelbrock claims a .32 second improvement on an SS. You have to do a little bit of cutting and welding on the passengers side catalytic converter flange for the install, but the rest should be a bolt-on operation.

    SLP has released exhaust headers for the SS, P/N #30006 ($326), and an installation kit, P/N #30025 ($88). The person to call at SLP is Joey @ 908-349-2109 (Toms River, NJ). Since they are aware of the NAISSO group, make sure you mention it if you call to order.

    One thing to be careful of when installing headers to the rubber boot for the grease cover on steering shaft. This rubber boot located just in front of fire wall but only about 1" behind the header. If you don't protect this from the heat, it will melt and leak all of the grease out. Use a heat deflector blanket to protect it.

    Another option is to have a stock pair of B-body exhaust manifolds extrude- honed. A thick, abrasive substance is forced through them, which polishes the insides of them and removes material from the places that most restrict flow. The cost is about $500 per pair, and another $140 for a new set of manifolds (they have a 1 month backlog). You will also probably want to port-match the manifolds to the gasket for maximum flow, and get the manifolds coated to preserve them and prevent excess heat from entering the engine bay. The honing is done by Extrude Hone, who has offices in both CA and PA. The CA office is 310-531-2976, while the PA office is 800-367-1109 or 412-863-5900. Extrude Hone is extending a discounted $375 price for any people who mention NAISSO or Scott Mueller's name. They also port match them to the gasket, and all flash is removed as well. Note that they do all of the SLP Camaro SS exhaust manifolds, so they have the right tooling for both F-cars and B-cars already setup. The casting used on the F-cars is exactly the same as the one used on the B-cars (Caprice and Impala), only the outlet is machined slightly differently and the heat shields are different.

    Jet Hot coating is done by MCCI Jet Hot (800-432-3379). Prices vary, but a set of manifolds will probably run about $125 or so.

    Team Dynotech is also considering to start extrude honing f-car manifolds. They are setting up tooling as we speak. The shop guy has done extrude honing on aircraft turbines for 20 some years, and wants to try something different. He's already done turbo housings for Norwood (Ferrari tuner). They are planning on doing this on a exchange basis so you wouldn't have to wait for your manifolds to be done. They will also port match to the gasket and remove casting flash. The tentative price is set to $360, which is $140 less than extrude hone wants. They will do a prototype set the next week or so and flowbench them before and after. I would think they could do Impala SS manifolds also once they have the tooling for the f-cars. Team Dynotech, ask for Chris: (214) 630-2878.

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    Leaded Fuel Only (Export) Exhausts

    Q: I'm moving to a country that doesn't have unleaded and need to remove the cats ;-). What should I do?

    A: Option NM8: "Exhaust System, Export Leaded Fuel". These are factory stainless steel pipes that directly replace the catalytic converters on vehicles built for shipment overseas. They do not include stainless steel bungs for the oxygen sensors, which you can obtain separately and weld on with stainless steel welding rod in the same locations as on the standard US pipes. Part numbers are 10204015 & 10204014 for the pipe assemblies and 10168551 for the gaskets (two needed). In addition, if you're doing any work with the manifold to pipe attachment, it's a good idea to have extra manifold studs on hand, p/n 10220453 (about $1, 6 total), in case they break. These studs use nuts, p/n 11516072 ($.75ea), but a better option is to use the metric equivalent from Totally Stainless (800-767-4781). One more thing: it's not a bad idea to check the condition of your O2 sensors, and replace them when you switch spark plugs or you have the pipes off and over 50K. The sensors are p/n 25165313 and are only $25.63ea. These work for '94-'95s, any may work for the OBDII '96s, but I haven't confirmed. And as always, anti-seize is your best friend with all these bolts. The O2 sensor bungs you need are available from Lingenfelter (LN0055-B) @ $6.95 each or from NAISSO for $10 a pair. Or, if you've got nothing better to do, they can be made out of 1/4" thick steel, 1.25" x 1.25" with a 21/32 hole drilled thru the middle. Then just tap the hole w/ 18mm x 1.5 tap and you're done! Other than having these bungs welded on, this should be a bolt on addition, with no major tools required. Most people have found a bit of a performance increase from them and a somewhat throatier exhaust note.

    Note that these pipes will not work on 1996 vehicles due to an additional O2 sensor after each catalytic converter to monitor efficiency. To make them work, you will need to order two secondary O2 sensor simulators from Caspers Electronics (847-247-0484). The simulators allow the '96 PCM to believe that the secondary O2 sensors are installed and functioning. Remember that this is not legal in most area, so use your own judgement when performing this modification.

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    Rattles Coming from the Exhaust System

    Q: There's a rattling noise coming from the rear of the car. Any ideas what to look for?

    A: Some, if not most, Impalas arrive with the rear exhaust hanger bolts loose or missing. Have them replaced or tightened at the dealer. Also, there is a heat shield that goes around the plastic gas tank that runs close to the exhaust. It can get resonate when a larger or noisier exhaust is installed.

    If the heat shield is rattling, try getting some thick sponge or that gray spongy packing material and cut it into four large pieces. Stuff the four pieces in between the heat shield and the chassis, front to rear. The pieces of sponge will act as a noise dampener.

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    Stock Exhaust System Removal

    Q: I'd like to remove my stock exhaust myself to install my new system. Is there an easy way to do this?

    A: It may be possible to do this job with only the rear of the car elevated, but it is easier if the front is raised slightly as well. Ramps will help get the tires off the ground (these are also useful for oil changes!) With the rear of the car on jack stands and the front on my ramps, there's plenty of room to work.

    Each side of the exhaust system is fastened to the rest of the car at three points: