Am presently running a reprogrammed PCM, engine always runs rich, I have a spare PCM from the same year car, what is required in order to swap them for testing? My goal is to increase the gas mileage, now probably getting about 10 MPG.

 

Have you done any diagnostic work to determine is there is a cause for the problem OTHER than the program?

Who reprogrammed it, and why was it reprogrammed (appears engine is stock)?

 

Engine is not modified. Reprogrammed because the truck tires are much larger than the car tires. Also wanted a performance boost which I think is the reason it's rich. Was programmed by a company in Tx.

No diagnostic work other than checking for codes, of which there were none.

My other PCM has not been reprogrammed. I was told it would be necessary to reflash it, whatever that means.

 

The best way to coax a few extra HP out of a stock LT1 is to lean it out, not make it richer. It's already programmed way to rich at WOT, from the factory. Note also, that for all practical purposes, you can only "tune" wide open throttle. The A/F ratio for "normal" (part throttle/moderate RPM) is hard coded and can't be changed.

I doubt its the tune. Tires, I understand, but that's not going to affect the MPG. Obviously a heavy 4WD truck will never see the 20-30MPG range of a stock LT1 in a 3,600# car. But it shouldn't be at 10MPG either. Just curious... what axle ratio are you running, because that has to be programmed into the PCM as well?

As far as swapping the PCM's, you just unplug the old one and plug in tht new one. Because of the tire diameter issue, your 4L60E shifting may be adversely affected, unless you have the new tire diameter (and possibly axle ratio) programmed (read - "flashed") into the unmolested PCM.

But I doubt your problem is the program or the PCM. Something as simple as misfires, exhaust leaks before the O2 sensor or faulty O2 sensors/wiring can cause the problem you are experiencing. What year F-Body is the LT1 engine and PCM out of? That will determine how you do your diagnostic work.

 

Thanks for the replys. Rear gears are 3:42, tires are factory size 265/70X16. I have noticed one exhaust leak, the connections appear to be tight, but looks like exhaust is leaking through one of the O2 sensors. I thought if it were bad I would get a code. While running down the road say 60mph, sounds like the ignition is breaking up. Although I have not changed them the plugs and wires look great. I have replaced the Optispark with a new Delco unit. The engine and harness came from a 1995 Camaro. I have added a ALDL port for testing.

All assistance is highly appreciated.

 

ttt

 

You won't get a code for an exhaust leak, unless its so bad that it drives the O2 sensors down below 200mV and keeps them there. Otherwise, the O2 sensor sees the air educted through the exhaust leak, the PCM figures its lean, and adds extra fuel the engine doesn't need. Runs rich, and wastes fuel. Misfires do the same thing.

 

Thanks Injuneer for the help. Would have been a dry run without you on the job. Thought there might be some tips out there pertinent to the LT1 that I could pick up here, will go ahead and sort it out myself. Thanks again.