I drive a 93 M6 Z28. A couple weeks ago I noticed a little misfire but didn't think to much of it. As the days went be the miss got worse and worse. I finally pinned down exactly when it does it. Anywhere between 2,000-3,000rpm at anything but full throttle. If it starts missing I just floor it and it goes away even at a low rpm. Even if I keep it part throttle it clears up above 3,000rpm. The car pulls fine up top. It does not do it at all when the car is cold, only when I have been driving for about 15min. I replaced the Opti, plugs, wires, tried a diffrente coil, and hooked it up to a laptop. Everything looked fine but the long term fuel trims were not changing much, they were just staying right around 108. Any ideas?

 

EGR would be my first guess. They stick and are usually a problem from just off idle.

No luck there, unhook an O2 and see what it does while staying in open loop.

 

EGR was delted from the car a long time ago. What would unhooking the o2 show me?

 

Unhooking the O2 sensors (BOTH of them) will put the car in open loop (power enrichment mode) all of the time. When you give it full throttle, it goes into power enrichment mode. Your O2's may be supplying false information and causing it to miss while running in closed loop.

 

Only have to do one of them, not both as it will throw a code either way. The point was since you say it runs good cold but not hot, try leaving it open loop.

Oh yeah, even if it's deleted, if the blocking plate is leaking air, same problem. So just cause it's not there doesn't mean it's not the problem.

 

I will deffintaly try that, thanks.

 

It's been a while, but I thought the car would throw a code if you only unhooked one, and it would still go into closed loop. DTC13 for left O2 failure and DTC63 for right O2 failure. If both are unhooked, no code and no closed loop. I could be wrong, but I don't recall getting a code when I did this. I've never tried just unhooking one and see if it stays in open loop.