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Fuel Pump Issues, No Prime When Cold

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86 MJ, 4.0, with 4cyl fuel pump, changed less than a year ago.


Anyway when I go to start the truck in the morning or after its been sitting for over 15min the fuel pump won't prime. And when I start it the truck will crank a long time but eventually start after about 5-10sec. But after it has been started and driven if I shut the truck off and turn the key back on the pump primes normally! I checked with a test light if I'm getting power to the resistor(which has been bypassed) on the driver fender, and yes I am, test for power down at the connection to the pump and I am getting power there too. Tested my ground and it has a good ground. Is there anything in between the resister on the fender and the connection before the tank? Ill go through it and double check tomorrow, I may have to check this out when the truck has been sitting for a bit. But any suggestions are greatly appreciated, thanks!

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I forgot to mention its a 92' 4.0 wiring harness. I tracked it down kinda. In the fuse block the ground circuit that is suppose to ground out the fuel pump relay and activate the relay had power coming back through it, and while I tested it the ASD relay activated, so both grounds are connected at some point and have power coming back to it. Take the ASD relay out and the pump primes like it would normally. BUT with the fuel pump connected at the resistor on the fender and I test the ground circuit and ground it out with the test light the fuel pump activates!

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