1994-1996 Caprice 9C1/Impala SS -- Knowledge Base

FAQ Section

• Q: What does 9C1 mean?
  A: It's an identification code (RPO code) that GM assigns as an option package for police cars. Every option ordered on a car is assigned a RPO code. Every GM car or truck made has a large list of RPO codes associated with it.
  
  
• Q: What is the wheel identification number (or rim part code) of the 9c1 rims with the bolt-on center caps?
  A: Stamped on the steel wheel itself is RGR. Some wheel shops need to know this when buying replacement rims. RPO code is N97. I don't have the GM P/N handy.
  
  
• Q: Why does my Optispark go bad every 30,000 miles or less?
  A: Chances are that the venting system for the Opti is clogged or damaged. A properly maintained Opti lasts 100,000+ miles...yes, in real life.
  
  
• Q: Why do my windows go up/down crooked? Or why do they grind?
  A: The plastic sliders in the track may have broken. They need replaced. There is an aftermarket version that is much better. It is a roller design and can be purchased at most parts stores under Dorman or Motormite pn: 74444.
  
  
• Q: Why is my ABS light on (dash light)?
  A: Either a wheel sensor went bad or a connector is corroded. I've needed to clean the rear harness on 3 different cars. The sensors are very reliable. The harnesses and connectors are not.
  
  
• Q: Why am I getting poor gas mileage on my stock motor?
  A: This could be caused by many things. Start with plugs and wires. Use Delco parts only. Then go over ALL of the vacuum lines. These cars are 20 years old now. I've seen many brittle and cracked lines. Then check the A.I.R. pump system. Mine had a stuck solenoid on the A.I.R. pump which was causing it to ingest fresh air constantly which confused the O2 sensors and made the car run rich. I deleted the A.I.R. pump system entirely, which is legal if you reference the TSB and affix the sticker to your radiator support. Next, check the exhaust system for leaks. Then check for bad O2 sensors. Then check for a bad MAF sensor. Then check for a bad MAP sensor. Some of these sensors may be bad, but not setting a code. I've seen MAF sensors behave like this. Check your cooling system. If the thermostat has been removed or replaced with a 160 degree model (and no additional computer programming has been done), it will run too cool and the computer may make it run rich. Finally, a new intake manifold gasket may be needed, some think this gasket is a chronic problem, I do not.
  
  
• Q: I hear a tapping or clicking sound inside the car near the firewall. It goes away when the car warms up. I don't hear it deep inside the motor.
  A: Chances are that you have an exhaust leak at the back of the manifold. This was a BIG problem on these cars. Every single unmodified iron head LT1 I've seen has either had a loose or broken rear bolts (on either side). If you haven't done this yet, replace ALL of your manifold bolts with grade 8 SAE 3/8"-16. If any bolts are broken, remove the manifold, check it for cracks, cut out the cross-bar between the bolt holes on the rear port (passenger side), remove the broken bolts, replace the gaskets and reinstall everything. If you haven't done this yet, do it NOW preventatively. Once a bolt breaks off in the head from heat stress, it is a big job to remove.
  
  
• Q: My exhaust sounds like there are rocks in it. WTF?
  A: There might be! I've owned a few B-bodies that had the converters fall apart. I found large pieces of material in the pipes. The pipes were partially clogged. The only temporary recourse is to finish hollowing out the converter by banging on it violently with a BFH (rubber hammer). Let the pieces fall out of the disconnected pipe. Or drop the converters entirely and empty them out. This is only a temporary solution. The car will sound like crap and will fail federal emissions. Plan on buying new converters. Replace them both at the same time. Use new grade 8 bolts everywhere. Use stainless steel converters when possible.
  
  
• Q: Car overheats all the time. Why?
  A: These cars have great cooling systems. But when a problem turns up, it can cause big headaches. 1) Replace the radiator cap (actually the coolant recovery reservior cap). 2) Check hoses and clamps for leaks. 3) Flush the radiator and cooling system. I do this by disconnecting the restrictor valve near the PS reservior. While you are at it, replace this valve. The plastic commonly falls apart internally. DO NOT BYPASS it with a straight pipe...instead, order a direct replacement from GM... They are cheap. If your car still overheats, 4) replace the thermostat with a 180 degree stock unit (I like the Stant Super Premium PN 45218). An upgrade is the Hypertech 160 degree unit (PN 1008; requires a PCM reflash). Most already come with a gasket, so no need to buy one seperately. Use a 1/4" drive socket to tighten the housing bolts. Do not overtighten (ignore the FSM for the torque spec on these bolts; it's wrong). 5) Replace the water pump. A rebuilt/reman unit is around $50. 6) Check the performance of your electric cooling fans. Does the primary fan turn on with the A/C? Does the secondary fan run on a hot day when the engine is very hot? Unplug the temperature sensor on the water pump. Both fans should turn on. Do they blow enough air to push your hand when cupped behind each fan in the flow of air? Check the fan relays and connectors. I've seen the relays fail, the wiring harnesses melt, and the brushes in the motors wear out...all of which will seriously hurt the performance of the system.
  
  
• Q: What is this jingle/jangle noise I hear coming from the front end? If I listen carefully with the windows down, it sounds like a pocket full of coins every time a hit a bump.
  A: Check the end links. These attach the sway bar to the control arm. After high miles, the washer holes elongate and shift on the shaft or the bushings crack, crush, or fall out. When this happens, the jingle noise comes from the washers themselves dancing around. Order a set of end links from your local parts store. They are common and cheap. Or build your own using long stainless steel bolts, washers, spacers, and bushings. If you build your own, you can control the preload on the sway bar and tighten (or loosen) the suspension response a little.
  
  
• Q: Inside blower motor (heat, A/C, vent, etc.) only runs on high. Why?
  A: The resistor pack has failed. These usually rust out. It is located about 10-12" to the left of the blower motor in the ducting under the dash. It has a plug with 4 wires coming out of it in a straight line. I have been able to repair these at times, but the best thing to do is replace it.
  
  
• Q: Were there differences between 1994, 1995 and 1996 Caprices?
  A: Yes. There were many subtle differences between those three years. I believe the '94 to have the best build quality. The '95 model year made some good design improvements, but build quality started to slip. Finally, the '96 model year was a bit of a disaster with build quality and consistency since it was the final year. I hope to write a separate page on ALL of the differences between those three model years.
  
  
• Q: I would like to donk, slam, or install 24" wheels on my car. Any advice?
  A: No.

Last updated: February 29, 2016
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