okay, my dad had a 90 geo tracker he let a friend of his borrow for a long while. we borrowed it for about a week and it ran fine, then about a month later we bought it and noticed the backfire.

when i accelerate it has a "pop" from under the hood and the vhicle jerks. sometimes it will make 5 or 6 pops in a row before it stops. it "mainly" does it at lower RPM's (below 3500), and while cruising at a steady pace it runs fine. when i give it gas it backfires again.

i have tried to adjust the timing both ways with no change, i checked the plugs,wires,dist cap,vacume lines and ECM codes with no luck.

what all could be causing this?

thanks.

Hi my 91 backfired in low rpm. It was holes in the exhaust. I found most of them and used muffler mend cream. The backfire and rumbling went away.
Hope this helps.

okay, it's fixed. on christmas day i finally had the time to tear it down. after taking the fan off to get to the balancer bolt, so i could turn the engine over i took the cam cover off to check the valves. as it turns out all 4 exhaust valves were stuck open a tiny bit. after adjusting it the backfire is gone, and it has twice the power. now all i have to do is replace the cam seal and fix the exhaust leak on the down-pipe. neither of which will be fun....

thanks.