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My truck is backfiring

Just got a 1990 k1500 with the 4.3 v6 and 5 speed and it backfires. A buddy told me it was shooting flames out of my exhaust. What does that mean?

A stretched/jumped timing chain will cause this.


Could it be anything else? I don’t really have the money for a timing chain…

LOL. I don’t think that whatever the diagnosis is will depend on how much money you have to fix it.

Since you just bought it, you might as well go over all of the basic maintenance stuff - especially those having to do with fuel and spark delivery. Its a good idea even if it doesn’t solve the backfire. Basically, if there is flame out the exhaust then there is a good chance that you’re getting excess unburned fuel down the exhaust. So you should look for reasons for that - things that flood the engine and / or cause unreliable spark. It’s mostly cheaper stuff than a timing chain - you might get lucky.

There are several things it could be. Late ignition timing could cause this kind of problem and a timing light could reveal whether the timing chain is gone or not if the timing mark is bouncing around when checked.

Even if the timing chain is a goner, it’s not an extremely big deal on this engine

Anything that makes the mixture rich can cause backfire. When my choke cable stuck the choke closed my truck backfired. That was easy to fix.

10 years later it stuck again, this time open, so it had a hard time starting.

If you don’t have the money to pay to fix a timing chain you really don’t have the money to fix the damage to the engine that will happen when it fails completely.

Perhaps you have the money for a diagnosis? It shouldn’t cost much more than $100-$200. At least then you could make a decision.

I gotta tell you, though, considering the 24 year age of the vehicle there’s a lot of possibilities. I’m going to guess valvetrain, perhaps sticking valves (perhaps fried) or worn out lifters or valve springs. At this age the timing chain and its associated components were a great guess, but Tester beat me to that one so I’ll go with the valvetrain.

By the way, how many miles are on the buggy?