Was wondering if someone can help me figure out this noise? I have a 85 T/A witha 305tpi. I recently took the top end apart and replaced all the gaskets, removed all the emmisions and egr. Had a custom prom chip burned. I set the timing to 6 degrees, no known vacuum leaks. I have not checked the fuel pressure yet, runs a bit rich at idle. Anyway, under hard excelleration it sound like it backfires just once and then its fine. This is repeated everytime you nail it and take the rpms past 4500. Its not a loud pop but still audible. Maybe to much initial timing? The chip has an aggresive timing and fuel curve. I have also modified the maf, by taking out the screens and fins. Removed and pluged the air tubes in the stock manifolds. The throttle body has all the vacuum ports pluged except the powerbrake booster, fuel pressure regulator port and the pvc port these are all hooked up. Anyone??? Thanks

 

What is the total timing advance?

 

Whoever burned your chip, had to have a base timing to start with. Check with him or try backing down the initial timing 2* at a time to see if it quits. It sounds like your catching an intake valve partially open and you could have too quick of an advance rate for a 6* initial setting. If that doesn't help you might have an intake valve set too tight. Just some idea's that might help. SBX