I recently learned that when it comes to the fuel delivery of these trucks, that instead of the fuel pump being turned off and one via (+), it is grounded by the computer to run the pump.
To further make things more complicated and pointless.. It is not just an (on/off) fuel pump, but one that has an operating range. As the computer detects the need for more fuel, it operates the fuel pressure regulator, as cranks the fuel pump to the needed PSI. So at idle, not much fuel is needed, the computer tells the pump this. As the need increases by acceleration, the fuel pump is turned up higher to match the need. Again, its done through grounding the fuel pump.
I am battling the same issue. I replaced the Fuel Pump, Fuel Pump Relay, Fuel Pressure Regulator, MAF
Sensor, Vacuum lines, IAC
Valve, Inertia Switch. When I went to get the codes pulled, the ECU
would not communicate with the code scanner. I had to conduct a PIN test at home with a jumper wire. I finally pulled a code even though the "Check Engine Light" was not on...
Code: 542= Fuel Pump Circuit Open, PCM
Not being given the most clear answer other then being told to keep testing things I have already tested, its becoming apparent it may be the Computer that has failed.
To make it really strange, I am only having this problem when the outside temperature is above 90 degrees. This may also be why the computer fails. There is a defect in it that once the ambient temperature exceeds 90 degrees, the computer has the issue from being too hot....
Should have this problem solved in a week as I am going on a ECU
hunt, and have to duplicate the scenerio to get the result. If it works, it may be something to check into. if it doesnt, I am stripping the entire fuel system and running an aftermarket system.