Sometimes when I turn the key on the gauge will show the correct level but then drops to E within a few seconds. Stays there most of the time but sometimes will jump back up and then fall. I had another gauge cluster laying around so I tried that with no changes to the problem. I also had another fuel pump sending unit that I know works so I plugged it in with no changes to the problem either. I haven’t started chasing wires and grounds yet as I am guessing that may be the problem. But I am not sure where to start. Sometimes when the gauge is reading correctly and I move the shifter or some other control it drops. Any help is appreciated.

 

It's in the wires.

 

lol pretty vague. which wires? wires to the pump? wires to the cluster? wires to the ecm? wires touching each other? wires shorting to ground? and it seems strange for it to consistently drop after start up without moving anything that would cause wires to move

 

Does it do it at any time or is it at a set time like 10 or 30 seconds or a minute. if so it's probably a loose ground most of the time they are on the sending unit Just start tracing the wires.