Car runs fine it seems until it gets to running temp. Then under light throttle it begins a "choppy" misfire. But when I let off and ease back on it it's fine for a few seconds before it starts again. This happened before and i fixed it by reconnecting a loose o2 wire extension. However this time all wires are fine. I redid them anyway, but nothing is different. Awful misfire and the occasional backfire. Any ideas? Thanks

 

A few things you can try...First try cleaning the MAF (don't touch the wires just spray it)...this can solve a lot of problems...also iv seen running non ac delco o2 sensors causing issues. Just a few ideas

 

any SES light? May want to check your wires at night for any arching and maybe check your ect sensor too.

 

I've seen a few threads with about the same thing, everyone says check the ICM/coil as the silver paste is usually gone. I also seen remounting it off of the head. I guess the ICM does not like heat very much.

 

I would run a data log looking at the temperature the PCM thinks the engine is seeing. A bad coolant temp sensor could be telling the PCM that the engine is cool when it really isn't, leading to a over-rich mixture and the symptoms you describe....

I haven't seem an ICM failure that exhibits what you describe but I guess anything is possible. They usually simply stop working when they get hot and resume when cool...it's very frustrating.

 

Scan it even if the SES light isn't on. There are several critical trouble codes that do not turn on the SES light.

You do realize you can go back and edit your original post, rather than deleting them one after another????

 

no ses. actually there may be another problem now that i looked into this. there is no signal at the obd port. 0 voltage. got to looking under the dash for the problem, and the wires are a mess. cuts, splices, tape.. a real nightmare.. im guessing the police did this when they sold the car. i think this is a job that i will let a local shop do, as i dont feel like rewiring the whole car.

as far as attempts at figuring this out, ive rewired the o2 extensions, using solder and shrink tube instead of butt connectors. redoing the wires fixed this last time.

plug wires are fairly new, and no arching is evident. (ive had this issue as well in the past)

the ect is my next move. along with cleaning the MAF.

Thanks to everyone for the ideas, I will post back if I get it figured out

 

I never would have guessed. Thanks for the enlightenment.

 

"0 voltage" where, on which pin? There is no +12V pin.

 

Must've been something wrong with my meter. I'm getting readings now. 5 and 7v. Misfire was either coil, maf, or ect. Replaced coil and ect, as they were both aged. Cleaned maf. Misfire gone.

Now I'm focusing on wire mess under steering wheel. The transmission won't go into od. Performabuilt stg 2. shifts When manually shifted through computer, but will not shift on it's own. Factory transmission had all gears. Stg 2 already returned to Performabuilt under warranty and checked out, as well as local transmission shop. I'm waiting to hear from Vince at Trifecta to see if tune could be the issue.