Rough Running
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Junior User
Joined: Oct 2003
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Rough Running
Hi. I have a 1986 Ford F-150 XLT 5.0 302 EFI Flareside. I have a little problem. It has headers, straight back duals (true) with no cat and 2 cherry bombs (dynomax). It will run PERFECT for about 5 minutes when it is compeltely cold in the morning, but then start running worse and worse therafter. It vibrates the truck SO much after about 20 minutes of driving, it literally makes random things i have in the bed hop up and down. It has ALL new sensors, O2, Map, EVP, all the temp sensors, ACT, everything. All the vacumm is new. New water pump and thermostat and water outlet. Cleaned out throttle body completely. Brand new fuel pumps, both external and in-tank. Brand new fuel filter, air filter, plugs, wires, distribtuor, timed down perfectly. New valve cover gaskets, Plenum gasket, bolts all threaded in perfect. Ran the computer through it, came out fine, ran it through a computer a a local shop, came out perfect, no codes. Fuel Pressure is at 32-35 PSI, depending, while running. With key on, engine off, it stands at 37-38. What else could Possible be wrong with it? Please, any help would be GREATLY appreciated. Thanks so much. (maybe anyone else with similar problem?)
Junior User
Joined: Oct 2004
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Ever replaced the round module inside of distributor? I had this one go bad once and it would do the opposite of what you described. Rough when cold but good after hot and finally it started stopping and going. Mine acts a little funny now sometimes because the garage didn't put dielectric grease between the outside and inside distributor module. A little WD-40 makes it roar.
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Joined: Oct 2004
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Does it have two gas tanks? If so there's two fuel filters, one on rail under driver and the other right after the switching valve in a small round canister about three inches tall. Could dirty fuel injectors cause it? Sounds like you have good no load fuel pressure. I had a problem recently where mine was doing the same thing at startup initially and then after it warmed up it would do like yours does and it turned out to be the MAP sensor, but I was getting the computer code for it and you are not so I don't know. I know one thing and that is you are at the right place for finding out what it is. This site has really helped me out with my old machine during the last three months. Good Luck.
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Elder User
Joined: Oct 2004
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From: Fleming Ga
It really sounds EFI related. Runs fine while cold and in open loop runs bad when it warms up and goes into closed loop and the computer runs the engine off the sensors instead off the hard coded open loop program.
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Elder User
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From: Fleming Ga
open loop and closed loop are the conditions the computer operates under. When the engine is cold up to the point it reaches operating temperature, The engine runs under open loop condition. What this means is that the sensors that tells the computer how the engine is running are not accurate yet because the engine isn't up to temperature. Therefore the computer ignores the sensors and controls the engine using the factory presets programed into the computer to determine the timing and amount of fuel, normally a little rich to be on the safe side. That is why this is called open loop because the circuit to the sensors is effectively broken. Once the engine reaches normal operating temperature the computer switches to closed loop and starts using the sensor imput.