Backfiring
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Senior User
Joined: Mar 2006
Posts: 175
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From: HALLSVILLE TEXAS
Backfiring
trying to figure out why my 86 6.9 all of a sudden has gone to backfiring out of the intake. it started doing this saturday and i towed it back home cuz it was making some very weird noises. and my air filter looks like someone took a torch to it.
Logistics Pro
Joined: Sep 2010
Posts: 4,411
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From: Victor, MT
Whoa....backfiring out of the INTAKE?! thats not good, I would recommend checking the fuel filter, the fuel system in general to be honest. That could cause any number of problems if its plugged or damaged from something that got into the tank and sucked through the lines.
Fleet Mechanic
Joined: Jan 2011
Posts: 1,709
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From: 8600 ft in Colo
A head gasket blown between adjacent cylinders could let one cylinder fire when the adjacent one is on the intake stroke.
A leaky intake valve could let combustion pressure back into the intake.
Somehow combustion pressure is getting into the intake...
A compression test would help find either of these conditions.
A leaky intake valve could let combustion pressure back into the intake.
Somehow combustion pressure is getting into the intake...
A compression test would help find either of these conditions.
Cargo Master
Joined: Dec 2010
Posts: 2,123
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From: Fort Worth, TX
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Logistics Pro
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Senior User
Joined: Mar 2006
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From: HALLSVILLE TEXAS
ok so i checked the fuel filter, it was new went ahead and put another one on it for good measure. compression checks out at 360-371 psi between all 8 cyl. truck only has 126K on it also i forgot to mention it has no cold starting problems at all. this just happened overnight. possibly the IP has gone bad and has thrown the timing way off? jumped time maybe but how?
Cargo Master
Joined: Feb 2010
Posts: 3,493
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From: NY
Cargo Master
Joined: Feb 2010
Posts: 3,493
Likes: 3
From: NY
No, I was saying that I thought he said the fuel filter was burned up, not the air filter. The engine wouldn't pop like that if it was too advanced, it would sound like a power stroke.
Fleet Mechanic
Joined: Jan 2011
Posts: 1,709
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From: 8600 ft in Colo
Wow, that's weird. I don't know how it could be backfiring into the intake with good compression all around...
The inside of the air filter was burned?
Is it backfiring consistantly, like a specific cylinder?
The inside of the air filter was burned?
Is it backfiring consistantly, like a specific cylinder?
Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
A weak valve spring could do it........ mine crackled out the exhaust when one exhaust valve broke a spring.
I would pull the valve covers and check for a bad valve spring......or rocker assy. If an exhaust valve does not open engine will force combustion into the intake on next stroke... so I'm told.
I would pull the valve covers and check for a bad valve spring......or rocker assy. If an exhaust valve does not open engine will force combustion into the intake on next stroke... so I'm told.
