Is it possible for a PCM to make car run poorly. My 93 Trans Am has 124xxx miles and I'm not so sure it's running like it should, obviously really rich but I hear there factory tuned like that.

Thanks,
Andy

 

It's possible for them to go bad, yes.. but it's not the first place i'd look!

 

Well I recently did, wires, plugs, o2 sensors, fuel filter, oil/filter and map sensor.

 

How 'bout the Opti-Spark distributor ?
I'd check that before the PCM....they fail probably at least 100x more often.

 

No ususally.. They typically work or they don't

 

hey alvin do you have any idea what could cause my car to be reving on its own and then after 3min stall out? its a new motor swap and i got the tune from you guys not to long ago i dont mean to steal the thread i just saw your name and thought i can get a quick answer thanks!

 

Please don't highjack threads. If you have a question, start a new thread, or PM Alvin.

 

Under what conditions is it running "really rich" - at part load/cruise, at WOT or at all times?

The stock WOT tuning is on the rich side. But the part load/closed loop tuning is a moderate 14.7:1 to give the best combination of fuel economy and emissions. If the ECM can't hold 14.7:1, its usually because its getting bad info from the O2 sensors. The typical problem is a "false lean" - the O2 sensors see air in the exhaust and assume its running lean. But this can be caused by leaks in the exhaust system before the O2 sensors, misfires, or incorrect voltages from faulty O2 sensors or O2 sensor harness wiring.

It may also be from several other faulty sensor inputs.
-coolant temp sensor indicating a temperature significantly lower than actual coolant temp, and the ECM setting a richer A/F ratio for "cold start".
-an erratic TPS signal that causes the ECM to think you are opening the throttle, and richening the mixture.
-erratic MAP signal indicating that the engine is under load

A scan, producing a data log of the sensor signals and ECM calcualted parameters will ofte point to the problem.

 

I had my 93 Z28 taken into a garage after it failed emissions. Using two separate diagnostics units, he came to the conclusion that the engine computer itself had gone bad, and that it was running on 'limp home mode' which did meant that it did not read any inputs from any of the sensors, and always ran in a full rich mode. based on the emissions readings I got, this definitely seems to be the case. bottom line- if you replaced all those sensors and your car still does not run right, it is very possible that your PCM has gone bad, and that could explain why it is running very rich

 

Well man I would still check more out.

I work in a shop and today we had a kia spectra come in with the same problem, but it was a broken wire comming from the computer to the MAP sensor, computers in my experience when they go, the car dont run at all.

Don

 

Those computers hardley ever fail, You wont believe how many cars may dad has fixed after the dealer or some other hobo that dosnt know what he his doing throws a computer at it because he cant read a voltmeter or a scanner. If your mechanic thinks its a good idea to throw parts at a car you need a new mechanic. You cant return a pcm so you better be sure that its the problem and if he cant tell you 100% that it is or isnt i would find a differnt one to work on your car.

 

The mechanic I went to may have absolutely no idea what he's talking about. But if the car starts running perfectly after replacing the engine computer, I will certainly let you know.

 

mine went bad two days ago

 

Borrow someone's PCM and see if it takes care of the problem before you invest in a new one. Once you buy an electronic part---it's yours for evermore.

When I modded my car, I bought a cheap used PCM and had it tuned---always keep my stocker just in case JMHO