2004 GMC 4500 8.1L fuel problem

Discussion in 'Medium-duty Truck Forum' started by 31-5window, Jan 28, 2014.

  1. 31-5window

    31-5window New Member

    Hi I am new here looking for some help. I am having problems with fuel system on this truck it runs out of fuel and the gauge reads 1/4 tank. I thought I had a bad primary sender so I replaced it. that was not the problem I went thought it the secondary pump is good, the fuses are good, the relay is good. this is how the system works....So after some research PCM monitors fuel level in both tanks when front tank is 2 gallons below rear tank. PCM see's this and sends a signal to energize relay and transfers about 4 gallons of fuel. this action continues until primary tank (front tank) level is low enough to accept the remaining fuel in secondary tank at which the secondary pump will run until secondary tank is empty. with that said I am not where to go next how do I test the system? I know front sender is good I know secondary relay and pump are good. so I have to believe its one of two things PCM or rear sender. Any ideas????????

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