1986 F250 Backfires
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1986 F250 Backfires
Alright I have a '86 F250 with a 351W and if I get over 60mph and have to take my foot off the gas suddenly my truck gives a nice big serving of black smoke that lights up the night sky, is this normal for that year and model and what causes it so that I can try to prevent it?
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I have a few leaks I think, I know of 1 for sure, the pipe is pretty old, the previous owner replaced a few sections but the leak is somewhere under the hood on the passenger side, and i'm not sure about the tune-up either, i've had this truck around 3 months or so.
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From: Stephensville WI
Sounds like 1 of 2 things.
First, it could be a vacuum leak. CHeck all of your vacuum hoses for tears or loose fittings.
Second, I had an old Chevy LUV that would do this when warmed up. It tuirned out to be the smog pump. There is a valve on the smog pump that is supposed to shut the pump output off when you lift your foot of off the throttle. Those valves get corroded and stuck with time. If the pump doesn't shut off, you get a backfire. I took the belt off of the pump (no serpentine belt on that old beater) which stopped the backfires.
First, it could be a vacuum leak. CHeck all of your vacuum hoses for tears or loose fittings.
Second, I had an old Chevy LUV that would do this when warmed up. It tuirned out to be the smog pump. There is a valve on the smog pump that is supposed to shut the pump output off when you lift your foot of off the throttle. Those valves get corroded and stuck with time. If the pump doesn't shut off, you get a backfire. I took the belt off of the pump (no serpentine belt on that old beater) which stopped the backfires.
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the distributer is known to do that with mustangs. the advance in it starts to stick and will cause it to back fire. my gt had this problem. you can take it apart and clean it or replace it. if you take that cap off and try to turn the rotor button. it should turn freely a little bit. if it is hard to turn and don't spring back then that is your problem.
Tuned
Joined: Mar 2004
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could be that you have no cat. but also Does that engine have the 2 smog/air pumps on it. If if does theres a check valve inline . if that valve fails it will backfire on deceleration.
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ok, well where exactly is the smog pump located, i'm only 17 and don't have the wealth of knowledge that all the guys on here are blessed with.
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Tuned
Joined: Mar 2004
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Its been a while since I had a 86 F250 but if I remember corectly there are 2 smog pumps on the front of the engine, passeger side near the top. they use a seperate belt then the fan and Altenator. If your standing in front of the truck looking at the engine. center wil be a Radiator hose. just to the left of that will be your smog pump. it has a hose that comes out of it and goes over towards the passenger side firewall.
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