'89 Ford F250
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Joined: Nov 2004
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From: South Jersey
'89 Ford F250
Folks, I have a finicky truck here. She's got a 351w and doesn't want to go. When I start her up cold, she seems ok. But when she's warm we get a nasty hesitation when pressing the acceleration about halfway. Now it's to the point where she's breaking up and missing. Really no acceleration at all. I thought maybe it could be something electrical. I have my own theory but I figured I'd ask what anyone else has done in a similar situation. I did do the basics a while back. Change spark plugs, wires, cap and rotor. Nothing else has been done. She is not an everyday driver, but definitely needs some attention now. I have seen some threads about acceleration problems but not quite like mine. I am curious as to what anyone thinks... thanks for the help!!
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Joined: Sep 2004
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Possibilities:
Failing TFI module or bad grounds. Both can exhibit temperature sensitivity, working when cold and then quitting when warm, due (most likely) to electrical threshold shifts with temperature. Usually this affects all engine speeds, but spark energy is more critical at high cylinder pressures so this may be a possibility.
Blocked fuel filter, blocked in-tank "sock", weak fuel pump, bad regulator. Perhaps the fuel system can supply the (high-pressure but low volume) needs at idle, but the pressure is dropping off as the required delivery volume increases. Rig up a temporary arrangement so you can monitor fuel pressure as you accellerate. If the pressure drops (it should rise), that would cause these symptoms.
Bad MAP sensor, TPS, or oxygen sensor is causing the computer to under-fuel the engine. One test would be to floor the throttle and see if the engine works OK. Under full power, the computer goes into open-loop mode and does not care about the oxygen sensor. If the truck runs OK at full throttle, but not part throttle, a sensor problem might be indicated.
Failing TFI module or bad grounds. Both can exhibit temperature sensitivity, working when cold and then quitting when warm, due (most likely) to electrical threshold shifts with temperature. Usually this affects all engine speeds, but spark energy is more critical at high cylinder pressures so this may be a possibility.
Blocked fuel filter, blocked in-tank "sock", weak fuel pump, bad regulator. Perhaps the fuel system can supply the (high-pressure but low volume) needs at idle, but the pressure is dropping off as the required delivery volume increases. Rig up a temporary arrangement so you can monitor fuel pressure as you accellerate. If the pressure drops (it should rise), that would cause these symptoms.
Bad MAP sensor, TPS, or oxygen sensor is causing the computer to under-fuel the engine. One test would be to floor the throttle and see if the engine works OK. Under full power, the computer goes into open-loop mode and does not care about the oxygen sensor. If the truck runs OK at full throttle, but not part throttle, a sensor problem might be indicated.
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