I put a rebuilt short block in my 95 z28. It starts and runs with 40 and up psi, but makes bad knocking type noise at under 2000 rpm. Rev above 3000 and smooth and it clears up for the most part. I already checked my stall and made sure wires are in the right order. Could it be the icm or somthing like that. It came up with no codes when i scanned it.

 

If it was detonation you would prolly hear it at all rpms, tho im not positive. Sounds like a rod knock or some sort of spun bearing. I had a rod knock once and it would only do it at a certain rpm like 2-3k

 

I have zero miles on the rebuild though. The rebuild was from a very good local builder. Could it be any thing else?

 

piston slap?

 

exhaust leak?

 

sounds like a lifter rocker to me...as you bring up the rpm and oil pressure the lifter pumps up and knocking stops

 

those are all good suggestions that i will have to look into. If my valves are going to low and creating the noise can i put the stock rocker arms on to see if it makes it stop.

 

I am also not sure about my icm because it was a cheapy from autozone and i have heard autozone electronics are crap. It cost about a third of what other places are chargeing.

 

i am really scared that it is a rod knocking. My rebuilder did the job almost a year ago and i just finished it up recently. He is going to think i was driving it the whole time, and won't care that it is broken.