The car is a 1996 Z/28, engine is stock internally (aside from a cam) and has about 146,000 miles on it. I know i've had an exhaust leak at the header on the drivers side, its been there for about a month and i drove the car mainly on weekends, recently you can hear the car sort of "pop" and backfire a small bit at around 1500 - 2000 RPMs, it backfires most of the time when driving a bit around 2200 RPMs or more and then when letting out of the throttle, it winds down and at around the 1500 mark is where a backfire or two occurs. It struggles a bit when driving, thats how i noticed it first, it wasnt driving right and the idle felt a little rougher than ussual but it didnt backfire until later on that night. You can noticeably hear it through the exhaust when its revved to 1500 RPMs, it sounds like a valve is not seating/sealing properly to me...i know these are vivid descriptions of whats happening, but maybe someone aside from me has had this same problem or one similar to it. I've checked for misfires and i dont seem to have any visible arks and its not showing any codes for it. My occupation is a amall engine mechanic (lawn and garden / arborist equipment), so i generally hear valve and head problems day in and day out, but like i said that was just my guess. I'd appreciate any oppinions or information you guys can give me. Thanks alot.

 

I had something similar on the 415 Mini-Rammed engine in my 86 Vette. The #5 tube on my TPIS long tube headers developed a very tiny hole, right on top about 3 or 4 inches from the head.

Wasn't large enough to cause any sound, but the engine sure knew it was there. Idle was rough, but no back-firing. Being tuned in on how the engine ran, I took time to check to see what was happening. That's when I found the tiny hole.

I welded it up and all returned to normal. My thinking is that the tiny hole was giving the 02 sensor fits and, again goes to show just how sensitive these FI engines are to leaks, both intake and exhaust.

Hope this helps.

Jake

 

i'll be sure to check that, until then there are no more sugguestions? no sensors that could be bad maybe? it just seems like a valve to me because the "leaking/popping" noise seems to be coming from one cylinder, and it backfires as if it were only one cylinder.

 

A pre-O2 exhaust leak will cause popping on decelleration. I would fix the exhaust leak 1st, disconnect the battery to reset the fuel trims, and see if the problem goes away.

Thomas.

 

i didnt know that would cause such a thing, so it sounds like thats WELL worth a try, i will be fixing my exhaust leaks and seeing how that goes, thanks guys, i'll be letting you know