I'm looking to buy a 94 z28 but it has a couple of problems that i'm not sure about. The guy said that it will start right up and run perfect while its cold, but as soon as it gets warm it starts backfiring. He said that while your on the gas it's fine, but as soon as you let out it backfires real bad. If anyone knows what the problem is or what it could be, please let me know before I buy it. Thanks

 

i think it sounds like a too much fuel issue.

too much unburnt fuel in the exaust...

 

Any suggestions on how that can be?

 

check your induction system for holes. What happened to mine was i have unmetered air getting into my throttle body past my sensor so it throws off the gas to air ratio which causes it to burn more fuel than necessary which screws your gas mileage and causes alot of left over fuel in the exhuast. I had a tune up and it mellowed out but it still is alil raspy due tomy torn induction boot.

 

Ask him how long it's been since the spark plugs have been changed. Fouled plugs maybe the problem.

 

Unmetered air would cause it torun lean, since the computer isn't compensating for the extra air. Not enough fuel for all the air coming in. It screws with your gas mileage due to the fact that you have to hold down the gas pedal further (to compensate for lack of power).

 

Oh.. I must have misunderstood what it was doing.. either way could it lead to his problem?

 

I don't believe so. To me, it sounds like fouled plugs. The reason he doesn't hear the backfire when cold, is the exhaust isn't hot enough to ignite the unburned fuel yet. Possibly the O2 sensors are so fouled that they are "seeing" a lean condition and trying to correct it with extra fuel. That would also explain no backfire when cold. The O2 sensors aren't used to adjust fuel trim when in open loop mode. I doubt it's my second guess, I'd check the plugs.

 

If any of the O2 sensors are bad the car should be throwing a code and the SES light would be lit. I agree with 02StangGT, check plugs/wires.

 

Thanks for all of the help. I appreciate everyone's suggestions. I'll let you guys know if I that was the problem. Once again, thanks.