1995 Lumina 3.1L Backfire at 2000-3000 RPMs

[blk95lumina]

Hello,

I recently purchased a 1995 Lumina 3.1L w/ about 145K miles.

The car had been sitting for 4 months, but started up immediately w/ no hesitation, idles smooth, accelerates well, etc.

I was told by the owner the car fails emissions.

The problem I am having is the car will backfire (sounds like a loud "pop" near the front of the engine) but it only seems to do this when the engine is warm and only between 2000-3000 RPMs while sitting in Park.

Under any other conditions the car seems to run OK and the backfire is not heard.

Any ideas on where to start?

Thanks.

[Bearwulf]

What codes is the diagnostic showing?

[blk95lumina]

The check engine light is not on, but I suppose w/ an ODB 1 there could be some stored codes.

Have not really worked on ODB 1 cars much, so I do not have a scanner nor did the local Autozone.

Any ideas on where I can pick up a cheap scanner or how to read the codes w/o a scanner?

Thanks.

[Schrade]

Originally Posted by blk95lumina

The check engine light is not on, but I suppose w/ an ODB 1 there could be some stored codes.

Have not really worked on ODB 1 cars much, so I do not have a scanner nor did the local Autozone.

Any ideas on where I can pick up a cheap scanner or how to read the codes w/o a scanner?

Thanks.

Scanner? Your desk drawer.

Beginning in 1994, you short pin "12" to pin "4" and once again turn the ignition switch to "On" without starting the engine.

The speedometer will display any codes using the same protocol as the 1990-1993 model but there are some changes in the designation for the modules plus additional modules are added:

Module "1" is still the CCM module.

Module "4" is now called the PCM module (Powertrain Control Module) because automatic transmission computer control was added to Engine Control Module in 1994.

Module 7 (on the 1996 model only) is the RTD module. (This is the Real Time Dampening module which replaced the Selective Ride Control module in 1996).

Module 9 is the ABS/ASR module number from 1994 through 1996.

Finally, Module "A", the DERM (Dynamic Energy Control Module --- the air bag control module) will be requested to show any codes.

Just like the 1990-1993 display, you read the codes on the speedometer and read the module number on the trip odometer.

Again, you can cause the codes to repeat by turning the ignition off for five seconds and then back on.

Turn the ignition off and remove the short to restore normal operation.