Snap, crackle, pop problem

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Mar 31, 2004 | 02:01 PM

Nev. Bronco

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Snap, crackle, pop problem

351m 79 bronco and tring to install all the smog parts. I think its all hooked uo OK but still has a bit of a miss and the main problem is that, as a fast pedal and let off rpm's up up fine but on the decel it snap, crackles and pops and back fires. The haynes book just state vac, its OK, emission problem ?. I checked the air bypass valve with and without vac and looks OK. New egr valve, all is tight. all lines OK. HELP, what could be the problem causing the decel backfires. Thanks

Mar 31, 2004 | 02:18 PM

danlee

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Joined: Aug 2001

Posts: 4,270

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From: Delaware

Check your Spark plug firing order.

Apr 1, 2004 | 07:07 AM

ashvalentine

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From: Addison,Texas

Quote:

the main problem is that, as a fast pedal and let off rpm's up up fine but on the decel it snap, crackles and pops and back fires.

The only reason (unless it is something truly weird) for it to backfire on decel ONLY is because there's air getting into the exhaust. The mixture goes rich on decel, but it doesn't ignite unless there's some O2 to ignite it with. So you've got an exhaust leak or the bypass valve isn't bypassing. I'd unhook the air to manifold hose (leaving the check valve in place) and see if it idles (if it dies, the check valve is bad) and then drive it around. If it stops backfiring the bypass isn't bypassing.

ash
['If it doesn't look for a hole in the exhaust.']