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I just put a new ZZ4 engine in my car and I took it to the track[Mid Ohio] and the engine stumbles between 2100 and 2300 RPM. Any ideas??? Runs perfect everywhere else.
i just got my 383 running and it seems to be having the same issue. i'm in the process of covering all the basics (timing, vacuum leaks, fuel pressure, scanner readings, etc.).
it's strange because i thought i had everything dialed in ok. once it is warmed up, it idles nicely and revs strong, with no hesitation. but while driving, under mild acceleration, it hesitates and / or seems to stumble around that RPM range as well.
hopefully others who have solved the same issue will chime in. i will keep you posted on my progress...
Do you still have the EGR? A bad egr valve can cause stumbles.
How old is the opti? Sometimes opti's can develop a dead spot at a certain RPM range.
Did you do any tuning for the cam at all? It could be loading up on fuel at that rpm or something assuming the physical stuff is all OK tuning would be where I'd probably look next.