wiring harness
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Joined: Mar 2003
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From: Mobile, ALABAMA
wiring harness
ive got a '90 f-150 with a 5.o EFI.......Does anyone know if one of the wires in the wiring harness could make my fuel pump not prime so it will crank? im having some troubles getting it cranked up 
it wont crank up sometimes...im thinking its because of a harness sawp i did about 6mo ago.....im thinking of just dousing it with gas an ending it all...i need help! 
it wont crank up sometimes...im thinking its because of a harness sawp i did about 6mo ago.....im thinking of just dousing it with gas an ending it all...i need help!
Last edited by nd4spd; Feb 17, 2004 at 03:39 PM.
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From: Virginia
A missplaced wire could keep it from priming.
I have never had a fuel injected truck, but on my mustang, if I turned the key on without cranking the motor, I could hear the pump run for a few seconds. If you do hear this, it means it's priming the system, but you still could have another problem in the fuel system, causing it to lose prime. There is a check valve in the pump that can go bad, a leaky injector can drain the system, and a leaky fuel regulator can drain the system. The best way to check all of this is with a fuel pressure guage. One way you can experiment, is if you hear the fuel pump, turn the key on and off a couple of times, and see if it starts better. This will pump up the system if it's totally drained down.
I have never had a fuel injected truck, but on my mustang, if I turned the key on without cranking the motor, I could hear the pump run for a few seconds. If you do hear this, it means it's priming the system, but you still could have another problem in the fuel system, causing it to lose prime. There is a check valve in the pump that can go bad, a leaky injector can drain the system, and a leaky fuel regulator can drain the system. The best way to check all of this is with a fuel pressure guage. One way you can experiment, is if you hear the fuel pump, turn the key on and off a couple of times, and see if it starts better. This will pump up the system if it's totally drained down.
Thread Starter
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Senior User
Joined: Mar 2003
Posts: 306
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From: Mobile, ALABAMA
well when i turn the key to the on position i hear two clicks, one under the hood and one i assume in the tank.....100% of the time when i hear the pump prime (a humming noise for a 3 or 5 seconds)it will start....ive tried everything but opening up the tank, im thinking of taking to the local Ford dealership, thx for the info....anymore would help me out though 
