Intake Backfire

[Scott_68B]

Any thoughts on what could be causing an intake backfire? #1 cylinder seems to be the culprit. I've done a compression test and have 160-170 in all cylinders. I tried moving the coils around to see if it might be ignition related, swapped plugs and tested the plug wires and no change. The engine is missing and backfiring regularly as #1 cylinder fires. Fuel pressure is about 55# and holds. When I pull the plug wire off of #1 it still misses (of course) but the backfire is gone. I have a 3.1 hybrid with a 2001 3X00 top end and a Delta 260 regrind. It was running great, I came off the freeway and it started acting up at the end of the ramp. Any thoughts are appreciated.

-- Scott

[candychevy87]

jumped timing possibly??? a constant backfire means it only fires when the intake valve opens??? this is fishy, pull off a valve cover and look at the cam lobes, one could be worn down, other than that its wierd

[cajuntractorman]

Any abonormal noise? Broken valve spring? Valve stuck opened?
Check vac with a vacuum gage, should be fairly steady 15-17".
If it jumps irratically, it is most likely in valve train.
if not check all ignition again. Fouled plug? Injector not pulsing?

[gpse3400]

yeah m ake sure plugs and pkug wire are good, also check your injector on that cylinder. You can do an electrical resistance test to start with.

[Superdave]

pull the valve covers and check the valve springs.. make sure they're ok on #1, also check for a collapsed lifter (lots of pushrod play) or a loose rocker.

[Scott_68B]

Sorry for the delay in responding to this. Dave has it right. It ended up being a loose rocker...#1 exhaust. Tightened it up and took a 1400 mile trip without a problem. Thanks for all the responses.

-- Scott

[IsaacHayes]

Great news that you're up and running again. Any pics of this beast?

[Ray Hamilton]

Intake gasket blown in an area away from water but bleeds into the intake port. Try squirting some some carb cleaner in the pvc hole and see if it smooths out.

[Scott_68B]

Here it is just before we left on the trip.

[Superdave]

badass!

[ForcedFirebird]

Nice ride!!!

Bet that thing screams