[SoCal LS-L]

Originally Posted by oab_au

Chris, Mac says that the engine clears up and runs fine over 4000. So that rules out a lot of things like a blocked exhaust, and a lot of mechanical troubles.
It really seems to me to be a spark timing or mixture problem, caused by, air leaks, fuel delivery??????

Harvey.

So whats the backfiring through the intake from then? Pre-ignition would be the prime suspect, but how could the signal from the crank sensor come prematurely? He has verified doubly that the crank and cam timing are correct.

I think it may be time to swap in a stock ECU and see what happens......