460 backfiring on deacceleration
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New User
Joined: Mar 2004
Posts: 6
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460 backfiring on deacceleration
1990 F Super Duty. Keeps backfiring on deacceleration. Loud enough to be at a gun range, can't keep mufflers in stock. I checked the codes and get different results each time. Note engine runs great otherwise, poor fuel economy but it is a 460.
Any Help would be appreciated as to cause.
Thanx
Any Help would be appreciated as to cause.
Thanx
Elder User
Joined: Nov 2003
Posts: 544
Likes: 0
From: West Virginia
dux, It sounds like to me your running a little rich. When that happens you don't get a complete burn in the cyclinders and the un-burnt gas collects in the exhaust and muffler. Then if you have the slightest leak in the exhaust and it sucks in air it will burn when you let off the throttle. This will cause the backfire and sometimes blow the mufflers apart...lol I've had this happen to me on an old chevy when I put a new carb on and didn't have it ajusted right. I blew two brand new mufflers off the thing. Also as stated above check the timing! Hope this helps.. 
Fitter
Fitter
Tuned
Joined: Mar 2004
Posts: 284
Likes: 1
Way back when I had a 86 F250 that did the same thing and there was a Air Pump Check Valve on the Emmission control Air pumps under the hood that went bad,, not sure if a 1990 model uses the same set up as my old 86 did but I actually ended up disconnecting the belt to the air pumps(2 pumps) and never had problem again and truck ran better and still passed NJ state emmisions testing,, matt
