Fuel pump on the way out

[remauto1187]

My 99 GMC Sierra started doing the dreaded "cranking over like a carbureted engine" before it would start. So i yanked the tank down and installed a brand new AC Delco pump ($50) and replaced the fuel level sender ($15). The damn sender didnt solve my problem, the gauge still does the same thing.
Full is right below empty, empty is somewhere near 7 o'clock...lol I have seen the needle go round and round like a second hand before too. The needle also shows a high frequency oscillation also. Im now thinking its probably the stepper motor in the instrument panel. So now i gotta get ahold of one from a salvage yard or fleabay to troubleshoot with.
Atleast it starts like a fuel injected engine now.

[Duct_tape123]

My moms '99 suburban has the same high frequency oscillation. This all started after I replaced the fuel pump assembly for the 4th time in 3 years. It must have something to do with the aftermarket sending units not sending the correct signal.

[MidwestSS]

or its the stepper motor in the cluster....

[remauto1187]

Doubt it could be the seder unit since its just a potentiometer which cannot induce or modify a dc signal and convert it to a pulsating ac signal let alone a high frequency one. From some internet scouring i have come across 2 causes. One just like Duct Tape said ...the stepper motor and the other being the PCM. The PCM is what develops the signal from sending unit and then sends a signal to the fuel level gauge stepper motor. Somewhere around 96-97 is when GM went to the PCM doing all that. Prior to that their was a module under the dash that shaped the signal from the sending unit before it sent it to the fuel level gauge.

[Duct_tape123]

I meant that the new sending unit could be the wrong resistance and the PCM is interpreting it incorrectly.

[remauto1187]

If it were the wrong resistance then i definitely would not have the same exact symptom as the orginal sending unit with the new one in there.