miss firing and bucking

**mattmc99** · 07-13-2011

I have an 02 grand prix gt that i am working on. Its a buddy of mines car and one day we was out riding around and started to have problems. Every time my buddy gets up on it, it miss fires and will buck.. I thought coil pack replaced all 3 still not fixed. Replaced the vacum map sensor and having the same problem. Then his temp light came on one day and fans run all the time. I CE light came on and said the coolant temp sensor was bad. I replaced it and now when you start the car the fans come on run for a min shut off and never kick back on and the car will start to over heat. But if i leave the coolant sensor unpluged the fan run all the time and the car stays kool but the temp gauge doesnt work cuz it is unpluged. I read on here it could be something to do with the PCM thats causing the car to miss fire and buck,and also keep the fans from coming on when they should... I really am lost i dont know what i should do can i reset the PCM or replace it from one in the junkyard. Or is the PCM not my problem at all?? any help would be great cuz this car has me lost ..

**Bedwards** · 07-13-2011

Originally Posted by mattmc99

I have an 02 grand prix gt that i am working on. Its a buddy of mines car and one day we was out riding around and started to have problems. Every time my buddy gets up on it, it miss fires and will buck.. I thought coil pack replaced all 3 still not fixed. Replaced the vacum map sensor and having the same problem. Then his temp light came on one day and fans run all the time. I CE light came on and said the coolant temp sensor was bad. I replaced it and now when you start the car the fans come on run for a min shut off and never kick back on and the car will start to over heat. But if i leave the coolant sensor unpluged the fan run all the time and the car stays kool but the temp gauge doesnt work cuz it is unpluged. I read on here it could be something to do with the PCM thats causing the car to miss fire and buck,and also keep the fans from coming on when they should... I really am lost i dont know what i should do can i reset the PCM or replace it from one in the junkyard. Or is the PCM not my problem at all?? any help would be great cuz this car has me lost ..

The misfire is likely spark plugs or spark plug wires. Always the first thing to start with.

**mattmc99** · 07-14-2011

all new all the ways around.. still have the problem

**EJOUIE** · 07-14-2011

I had a PCM go out on me a little while ago... I brought on a reign of chaos when it decided to act up. Not only was it messing with the engine causing misfires, it began to pick on the poor transmission as well. I think a junkyard one would be your best bet, or one from Morad.

**mattmc99** · 07-14-2011

Thanks it seems like that has to be my problem. If i was to get on from the yard would i have to reprogram it to work with his car ?? Or is it a straight swap ?? And he has had some tranny issues since it started acting up. So i guessing the PCM controls shift points as well ???

**EJOUIE** · 07-14-2011

I am certain it does. I was driving on the highway and it acted up causing random downshifts which revved the crap outta the engine.

I think an 02 will need a case learn or something like that, but I dunno if another 02 gt PCM needs it though. Any 98-02 GT PCM should work.

**blueguy** · 07-14-2011

Have you checked the MAF sensor?

Unplug it and see if it still does it.

Before you replacing a PCM...that is a rarity...if EVER goes bad.

**JoRoW99** · 07-14-2011

Spray all around the engine and vacuum hoses with starting fluid or carb cleaner. if the idle changes, you have a vacuum leak. Mine was running really rough (I could feel it just sitting in the car) and i also had a lot of missfires with brand new plugs and 100% functional plug wires.. I had a big vacuum leak.

**mattmc99** · 07-14-2011

I still think it is something in the computer. Cuz when it is in park it run through the rpm range fine but when you drive it will buck. If your easy on the gas it runs fine but at wot it bucks and miss fires. I changed almost every sensor but the knock sensor and still cant fix it. Also i have checked all the vacum lines when i changed the vacum map sensor. I still cant get the fans to kick on either. I was wondering can i take it and have to computer tested at like a speed shop or should i just replace it with one from the junkyard. Can i even do that cuz if you buy a new one they need you vin number so will one from another car still work ??

**EJOUIE** · 07-14-2011

I do agree with blue, the chances of it actually being the PCM are low. My situation was an oddball, which sorta makes sense as mine is a 97.

I would check the ICM for the misfires, and possibly the T stat for the overheating issue. Then consider the PCM.

**mattmc99** · 07-14-2011

I have replace the maf with 3 different ones from the junkyard and didnt fix the problem. And i put in a new T stat bout 3 months ago and i removed it to see if it was bad when he started to have problems with the car and it was fine. I am almost sure it has got to be something to do with the computer.. I am thinking i should take it to have it hooked up too a tuner to see what going on inside the computer.. But also would the crankcase knock sensor cause it to run like that if it goes bad ?? but that still would not explain why the fans are not working right..