I have replaced the fuel pump, i have disconnected the alt, and the fuel pump still blow the fuse after the car starts, it will start and run for about 5 seconds the blows. It doesn't blow the fuse until you start it.
It ended up being a bad oil pressure sending unit, it is in the power loop for the pump. When the oil pressure would come up when started that is when the fuse would blow. A friend who works for a mechanic in town found a diagnosis digram for the fuel pump and that is how we found out that the the oil pressure sending was in the wiring loop for the fuel pump
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You may have a short in wiring to fuel pump. Try this! remove the wires from fuel pump, then turn key to start the car briefly. If the fuse does not blow, its likely the fuel pump is drawing to much current and blowing the fuse. God-Bless!
disconnect the fuel pump and place a new fuse in the holder if it still blows go back to the relay and disconnect it and fit a new fuse. In the first instance if the fuse stays good the replace the fuel pump as you have a dead short in it.. If it blows at the relay replace the relay as the short will be there.
Unplug the connector at the fuel pump. Install a new fuel pump fuse. Try to start the car. Does the fuse blow? If not that the problem is probably a bad fuel pump. If the fuse does blow with the pump disconnected than you need to look for a short in the power supply to the fuel pump.
The most common cause of this is that the fuel pump is drawing to much current due to wear and a possible burned fuel tank connector at the tank. To replace the pump you must raise the truck up and remove the fuel tank. Also replace the fuel filter which is on the inside of the frame on the drivers side. Use a rag to cover the fuel line when disconnecting it with the required special tool.
Sorry to say it could also be a faulty ECM. The ecm uses circuit boards to provide grounds to a bunch of components and can short out internally. Most of those components can fail and cause the same problem by causing a short "thru" the ECM. Things like injectors, O2 sensors, and so on. I doubt you will find the problem without a book and some test equipment.
the fuel pump and radio are not on the same circuit, most liokely the fuel pump is shorted, that is the most common cause, get under the truck and disconnect the fuel pump connector at the tank, if the fuse doesn't blow then u need a new pump.
You could have a short in the wire harness to the fuel pump or the fuel pump it self is bad or the relay has gone bad also. Start with the replacement of the fuel pump relay and also find the wire harness to the fuel pump sending unit from the frame to the gas tank and disconnect the connections. If the fuse does not blow when the connection to the fuel pump is disconnected, then it's a go chance that it's the fuel pump. If the fuse blows and the wire harness is disconnected, then the problem is towards the fuel pump relay and fuse block. Good luck and keep me posted, be glad to help you get your car running 100% again.
disconnect wiring to pump. install new fuse for the pump and turn over ignition. the car wont start because the fuel pump wiring is diconnected. check the fuse to the fuel pump, if the fuse did not blow when the pump is disconnected it is a faulty fuel pump. I read this somewhere and a garage is up to 850 dollars in parts and labor only to offer me more parts and labor not relevent to my problem. I am towing it home and running this test my self.