Been trying to track down this problen for quite some time now. The car runs great when cold and will rev all the way up but once it gets warm it misses horribly at high rpm(4k and up). Its like i hit a rev limiter.

-new opti, cap and rotor looked fine.
-plug wires 1 year old.
-new fuel filter.
-will be changing out plugs with ngk tr-55gp soon. probably stock plugs.
-maybe an oxygen sensor problem?

thanks for any help you have to offer!

-andy

 

any thoughts?

 

Several possibilities:

-something is heat soaking and not functioning correctly when its hot. IC Module (see Shoebox's page for a fix) or the optical sensor module in the Opti are possibilites. Weak plug wire insulation more likely to break down at high temps, etc.

-coolant temp sensor for the PCM is not providing accurate temperatures, PCM is not able to tell the engine is warmed up, thinks its still cold, doesn't fuel it properly - would likely show up at all operating RPM, not just over 4,000rpm.

-problem related to open loop (cold) vs closed loop (warm). Engine runs fine in open loop because the short term fuel corrections are locked out. When the PCM enters closed loop, the short terms are now used, and they are "overcorrecting" due to a false lean or rich condition.

A data log using one of the popular free scanning softwares may help identify the problem.