I have a quick question....

I have a 97 Z28 LT1 A4 with a cold air intake and SLP Loudmouth catback setup on it. When I get on it hard it pulls great and doesnt miss or backfire or anything ....when I let off after doing so it will sometimes backfire or make a popping sound in the exhaust. i have new plugs on it and new wires and they are good and its not pig rich anymore. All the air intake elbow is sealed and my MAF sensor is facing the right way...

is it because of the cold air intake and exhaust that it does this? anyone else get this problem? I can recreate it by downshifting the A4 trans and letting the engine slow itself....

 

I have a 95 with similar intake and exhaust setup and it gets pretty loud when engine breaking. Not sure if it's bad or not to tell you the truth....

 

Has the exhaust been installed recently? I know that my exhaust has a leak at a connection and it likes to backfire on decel at about 2000 rpm.. but i kinda like it.. lol.

 

anyone else know why this happens? there are no exhaust leaks plenum leaks etc..... is it bad? does it mean my cars not tuned right?

 

Mine has done it since I owned it. I have added headers, cutout & changed many things included a tune and still does it. Someone said it was unburnt fuel that was causing it. Not sure myself.

 

Check plugs and or wires.. I have found that anytime I have a backfire it's from burnt plug wire... Good luck..


Bill

 

If you just hear a little popping thru the exhaust, IMO, this is completely normal. You are hearing it more because of your cat back.

I believe mrmint69 is right. When the engine is at high revs and you suddenly let off the gas pedal, the throttle body closes and you have a very high manifold vacuum... the engine is spinning fast but the throttle is closed. This (temporarily) screws up the mixture of air and gas and it doesn't burn completely, so you hear it pop as it hits the hot exhaust manifold or cat & burns there.

When I replaced my stock cat back with the Corsa, I could hear it more. I kind of like the sound, actually.

But if you have a true backfire, that's different. That's a problem that needs fixing.

 

Yeah I think its the pops that you are describing that I hear. Not a true backfire. I was just wondering if it was bad or not, but it sounds like other people have the same thing so I guess I'm good.

 

This is exactly what it is, unburnt fuel. It will not harm your car or exhaust in any way. If you watch racing you will see some cars that belch flame out the exhaust durning decellerating into the corners.
Before the car makers connected the igintion to the streering we used to decellerate with the ign. off to build up gas in the exhaust, then when you turned the key back on,...KABLOOWY... You scare the heck out of the whole neighborhood. Only damage it caused was an occational split muffler.