I have a 1992 K2500 with a completely stock tbi 350 with 160,000 miles on it and am getting a backfire through the exhaust when decelerating. It runs fine when cold but once the engine gets up to operating temperature, it backfires whenever I lift my foot off the gas and don't push in the cluch. I have talked to a mechanic friend of mine and he said it was doing it becuase I don't have a cat on it but it started backfiring before I took the cat off(which was fine when I took it off). I've put new plugs, wires and distributor cap and rotor on it but haven't messed with the ignition or timing otherwise. The only other thing I can think of is the timing chain but i haven't had time to inspect it yet. I can also sometimes feel it surge or gain and lose power very slightly going up hills at speed on the highway. I have heard that this is a sign of timing chain slop but could it cause this backfiring? All of the mechanics I take it to tell me not to worry about it unless its doing it while i'm on the gas but its annoying as hell:mad3:
So to sum it all up none my mechanic friends want to bother with my cheap ass and i'm pretty well clueless:grinpimp:

Sometimes a leak in the exhaust system up near the headers or manifolds will do that, it sucks in air on deceleration and causes the backfire.

Yep,

what he said. I had a small hole in one of the collector gaskets on my truck and it backfired all the time while slowing down.
Changed the gasket and problem solved....

Mine does the same thing, when I let off the gas, figured it was a gasket. Damn headers, they never seal right!

Or? you need to check your initial timing, and use a scanner to check if it's going closed loop. Today's tune up should include changing the O2 sensor.

i'd vote for the exhaust leak sucking air

My S-10 does the same thing and it has a big hole a foot from the exh. manifold so I would check the exhuast really well first! It only does it on deccelleration which I like sounds cool on the 4 banger only thing cool about my DD!

I'll bet you guys are right. It does have a small exhaust leak but i had never heard of a leak causing backfires before. I've never really paid attention to it until now but it definitely is close to the engine. I'm thinking its either the manifold or gasket on the passenger side but I couldn't tell for sure. I'll check it out in the morning and give you all some feed back.

also check under the heat shield for a cracked manifold

Exhaust leaks are the main cause. You take your foot off the accelerator and you cut off air into the engine, the fuel can't ignite for lack of air, but once it gets into the exhaust system and air is supplied via a leak, it will ignite.