Backfiring!

[fishermike]

So, the other day I'm driving around town, 25 mph residential neighborhood kind of stuff, when my truck goes KABLAAM! out the tailpipe a few times. I shut it down, being close to my destination. When I went to go home a few hours later, no problem.

Until the next morning, when I go to start it up, and, you guessed it - KABLAAM! and it stalls. We're talkin' rifle report, not cough. Well I try again, same response. TSM says maybe an air leak into manifold vacuum, but that's a bit hard to find with the motor off and no vacuum pump! I changed a few suspect hoses, messed with the timing a bit, no improvement.

I live in a quiet neighborhood and have to work in the street (ugh) so finding the solution with as few additional backfires as possible would help me keep the peace! Thanks!

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-Mike
'85 GW "Cherry Bomb"
360/727/229/44/20/3.31
Flowmaster, K&N AF

[bignblue]

In addition to checking your timing, check the mixture as well. Mine was running rich last year--veeeerrrry rich--and backfiring like you wouldn't believe. It was blowing so much unburnt gas out the tailpipe that the pipe temps were igniting it, or something like that.

[Drew M]

Some possibilities in no particular order:

How many miles on the motor - wonder if the timing chain skipped and messed up your timing. Check timing visually - verify dist. rotor points at #1 post on cap when piston is at TDC - check timing mark on harmonic balancer and piston height(pull the spark plug) to verify TDC. They match up? Yes, then it's probably not a timing problem. No, change the timing set.

Does the back firing only happen when you let off the gas suddenly - then you have an exhaust leak (or extreme gas/air mixture lean out).

Good luck.
-Drew M.
Pull the plugs and check their condition - they'll let you know how each cylinder is working and give insight into the problem.