Newbie
What's Causing My Backfire?
1986 Chevy G30, 200k miles. After a recent 200-mile highway drive, engine backfires and puts black smoke out the exhaust. Suspected head gasket failure between #5 and #7 cylinder, but replaced HG and problem persists.
Low compression in #7 cylinder, half-burned fuel shot back up #7 intake runner. Valves are fully seated; springs, pushrods and rockers passed visual inspection.
Ideas? Thanks in advance,
-joe & christy
Enthusiast
Highly suspect valve issue here with the low compression and the popping in the intake runner.
Inspect the entire tract of that cylinder's intake intake and exhaust valve:
Valve, spring and damper spring, pushrod (straight), lifter down below, remove and inspect. I'm not sure that collapsed lifter could cause a backfire, possible.
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Enthusiast
internal crack in between intake runner and exhuast?? did you have heads pressure checked when doing the HG's??
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