Had a misfire a few months back. Chased it all over. Heres the symtms.
Tipping in at cruise speed, misfire light popping, floor it, goes away til about 5000-5500 area then returns and slows down on rpm. Replaced, Opti, plugs, wires, ICM, coil. Aluminum elbow, no rips. I found two loose spark plugs, tighened them, Car ran awesome. Ran awesome for about two months. Went to the drag strip, car felt alittle slow. Next day ran like crap, light light misfire. Drove home that night , was doing the same thing, light misfire on tip in (at 60-65) Parked car. Found two more spark plugs loose, tightened them. Took car for test drive, felt strong again, sideways on the 1-2 shift, was happy. U turned to come home after a 1 mile cruise, stood on it; light misfire again. Seems to me this only is happening when its warm. Cold it ran nasty fast. Warm up missfire returns. I have searched researched, and find nothing but the same answers.
How can I check items I have replaced? How can I eliminate?

 

O2's maybe?

 

thats the thing, no codes, I keep reading and finding new avenues. I'm down to egr, O2's, fuel preasure

 

I know you checked it, but I would make SURE air isn't getting in past the MAF. I had the same problem (only when warm) and turned out underside of rubber sleeve for my Al. elbow had a slight tear in it. Other than that, I'll let others chime in Actually, for some reason my car gets a lot of false knock when its warm , try checking that? I just tuned it out.

 

I'm using marine bellows over top of the aftermarket air inlets. No leaks. Going to try a coil and spacer (washers) and perhaps a ICM. *SIGH* maybe I can collect on the insurance. I'll be sure to invite everyone, bring your wienies and marshmellows

 

It sounds like you have a faulty plug wire...working intermittently.I would check it in the dark,running...pop the hood,and look for arcing.

 

I would not think fuel pressure since it only does it once it warms up. Easy to check with a gauge though.

 

I've got the exact same problem. I jsut replaced the opti, o2's and all my vacuum lines were bad, so I jsut fixed those leaks and it didn't change.

right after I changed out my o2's, it seemed to fix it for a few days, but I got the cheap brand o2's and not delcos. I think since my fuel pressure regulator wasnt hooked to a vacuum line, it foul'd the new o2's right away. I'm gonna replace teh o2's again soon but I never get around to it since I bought my daily driver

 

I had the same ptoblem and it turned out to be part of the wiring harness touching my LT's. It had partially burned the harness and the PCM wasn't getting a crank sensor signal. Check your wiring harnesses around your headers....

 

Check the wiring harness that plugs it the opti ,mine would heat up and the wires would not make good contact and miss fire. finding it was a nightmare . But with the motor up to temp ,unplug wires out of opti and unplug from conn,on the pass ,side of intake .Omh wires while shaking and moving the wires and plug .

 

thanks everyone I'll try each one by one and post results of what it is