maybe i can better help here......but my 91 z28 is backfiring i believe.....when im going down the interstate at 70 mph and up and let completly off the gas i get a loud pop in the back of the car. it will not do it at lower speeds and it wont do it when im giving it gas and if im at higher speeds if i just ease off the gas slowly instead of just completely letting off it wont backfire. car is pretty much stock. has the original exhaust. the cat is no longer there and the previous owner cut off the tips at the muffler. this just started monday. any suggestions??

 

Check your timing

 

wouldn't the car run bad if it was the timing? the car runs perfect and idles perfect

 

I actually have the same problem, except my 87 T/A is slightly moded. Its a 350 with a 5 speed, and if i rip around town and hold it at like 3000rpms, then rev it, then get off of the throttle, and throw it in neutral, it pauses then backfires pretty loud, i'm stumped myself, i think i'm runnin my timing high, but i didnt think it was timing.

 

I had EXACTLY the same problem on my Trans Am. Pull the distributor cap and check out the rotor. From what I was told the rotor was missing a few screws.

 

my brother-in-law told me to change the distributor cap and something in the distributor and wouldnt hurt to change the plugs. so thats gonna be the first thing i try and hopefully that'll be it