Is my LP shot?
 

New member here. I've had 4 Duramaxes before selling my last one and stumbling upon a rusty 1997 single cab Sierra for $1800. I'm a fan of this truck already, even though it's going to be a major project to restore it.

Today I was changing the oil, as well as doing the fuel filter. Everything went fine, except I couldn't bleed the fuel system. No fuel would come out of the little bleeder opening on top of the filter, and I could not hear the lift pump working. I put the old filter back it (it's disgusting!), still no luck... jumped the relay with a wire, still nothing. Finally after several hours of messing around with it, it finally sputtered to life and now runs as it did before. In those 2 hours of jumping the relay, swapping filters, and cranking it over a lot, I did hear the pump kick on only once. It's pretty rusty... I'm guessing it's shot? But if so, how is the truck running without it functioning? I crawled under the frame with the truck running, and it doesn't seem to be making any sounds.

The IP can pull fuel through a non working LP but it puts alot of stress on it.

Thanks for the reply. Does my truck wire it through the oil pressure switch, or is it through the ECU? Just trying to see if I should replace the lift pump as well as that oil pressure sensor.

I'm not an expert, maybe someone who is will jump in here, but I think 97 should provide ecu backup power if the ops fails.

With the motor running , open the t valve wide open. Motor stays running =good lift pump. Motor dies=lift pump not working, then diagnose further to see if it's getting power or not.

If in doubt, throw it out! Id' replace the LP before it leaves you stranded....