Loud Backfire on decelleration

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Sep 9, 2001 | 11:42 AM

bulabula

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Loud Backfire on decelleration

Once per trip now, it seems I have a LOUD "BANG" backfire when decellerating on the highway. It never happens in town. I noticed it more often pulling the boat (16K combined weight) but it happened yesterday w/o pulling a load. The first time I heard it I stopped and checked all 12 tires to make sure none of them blew.

I'm worried about blowing my muffler/exh system, or worse.

I am running regular gas, 12 degrees base timing (checked w/spout pulled), temps are normal, new cap/rotor, plugs are tan-brown, and I do have a leaky exhaust manifold on the driver side, fwd cylinder.

Any ideas on the cause?

Chris

'88 F350 XLT Lariat CC DRW/7.5l/C6/4.10
'93 Mustang LX 5.0l/T-5/3.55's/Flo's/pulleys/K&N/Synthetics
Nissan p/u (DC commuter)
Volvo 940

Sep 9, 2001 | 12:18 PM

Franklin2

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From: Virginia

Loud Backfire on decelleration

Do you have a smog pump and catalytic convertor? That is a heavy truck and might be exempt from some emission stuff. If it does have a smog pump, I would suspect something wrong with the smog pump control system. Check all your vacuum line connections to these components. What is intersting, is the manual says when pulling a load, extended idling and warm up (all rich conditions) the diverter valve doesn't let the smog pump, pump air into the catalytic convertor to keep the convertor from overheating. If you do have one, I wonder if your exhaust leak would introduce air into the exhaust and cause a problem?