What causes backfire through the exhause? - Chevelle Tech
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post #1 of 8 (permalink) Old Sep 25th, 04, 4:19 PM Thread Starter
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Hi Crew,

I am having a problem that is not really bad but it is just an anoyance.

My big block slightly back fires through the exhaust pipes when the engine is cold but goes away when the engine warms up. Awhile back, I did a cam, lifter and valve spring change but it ran ok at the time.

Has anyone experience this before?

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post #2 of 8 (permalink) Old Sep 25th, 04, 5:13 PM
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If I am not mistaken, the engine is firing when the exhaust valve is slightly open. I don't know for sure, but that sounds like it. Maybe check your timing. Too retartded? Maybe someone will chime in with a more direct answer.

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post #3 of 8 (permalink) Old Sep 25th, 04, 9:49 PM
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Maybe it is a leak at the exhaust manifold? I have heard that they can sometimes cause a backfire in the exhaust. Also like RedSS454 said, might be timing.

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post #4 of 8 (permalink) Old Sep 26th, 04, 3:56 AM
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Lean Mixture
Incorrect Valve timing
Incorrect Ignition timing

Alot of things really

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post #5 of 8 (permalink) Old Sep 26th, 04, 8:48 AM
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Usually, when you backfire through the exhaust it's an A/F problem or a secondary ignition problem.

If it backfires through the intake it is a timing issue, either ignition timing or valve timing.

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post #6 of 8 (permalink) Old Sep 26th, 04, 2:30 PM
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check to make sure the exhaust manifolds, or headers if you got em' aren't leaking. I was having the same prob, I replaced the header gaskets on both sides, prob. solved
read your plugs too.. could be a bit rich..

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post #7 of 8 (permalink) Old Sep 27th, 04, 10:01 AM
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If it's backfiring thru the carb, Is the ignition too advanced? My engine will do it every so often, usually under load or just before the trans downshifts. Single pop thru the throttle body, then it's fine. I have computer controlled ignition, so I will have to alter the timing map if it's wrong.

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post #8 of 8 (permalink) Old Sep 27th, 04, 1:59 PM
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I am having the same problem. And it is only out of the left side exhaust pipe. Perhaps that side is loose.

My 396 timing was at about 18 degreese btdc when I checked it. That seems about right to me.



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