North American Turbocoupe Organization

Full Version: missfiring above 5500 rpm
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My 88 t-bird missfires and starts shaking real bad when it hits 5500 rpm. I have replaced the spark plugs, tps, coolant sensor, o2 sensor, distributor and nothing. I have tried another coil, pcm, bap sensor, vam, and have yet to figure out the problem. Can anyone help me out? thanks
How many miles on the head components? Might have weak valve springs and the valves are floating??
Well this problem started ever since I changed the headgasket. The other head that was on it was craked replaced it with a good turbo head. The car already had a roller cam but I do not remember if I changed the valve springs or If i installed the same ones. When I rev it to 5500 the engine pops and then starts shaking and missfiring.
Let's see if anyone else has other ideas. "Engine popping" sure sounds like valve float, especially since it's not occurring until fairly high rpms and you have replaced a lot of the usual suspects already.
Should have come here first before throwing parts at it..... O2 sensor output is ignored over 3000 RPM if load exceeds 10%, so the O2 isnt the problem. PCM for sure is nt the problem. I agree with Pete... valve float, especially if it happens at the same RPM every time. Also, have you chwcked your fuel pressure under loadto be sure the pump is keeping up?
I have not yet checked the fuel pressure yet but It does smell gasoline after i rev it and starts missfiring.