Lift pump problem

[NeedMoPower]

I just bought a new to me 98.5 and have been doing some routine filter changes and added a fuel pressure gauge as well. I'm noticing that when you cycle the key you can hear the lift pump (stock) prime and the gauge reads 13 psi, but when you crank the truck the fuel pressure drops to 0psi while at an idle and the lift pump stops running. Driving down the road the gauge continues to read 0psi so for whatever reason the lift pump will not run when the engine is running.

Has anybody ran across this before or have any suggestions where to begin looking?

Thanks

 

[12vdiesel]

Back probe the fuel pump connector with a multimeter. See if you are getting power to the pump. Check fuses and relays as well.

 

[NeedMoPower]

Thanks for the tips. I'll check voltages in the morning, but i know the pump is getting power if it will prime with the key cycle. Is there a particular relay that is responsible for keeping the pump powered when the engine is running?

 

[12vdiesel]

There is I am not sure which one it is though. Try looking on the fuse box lid. If nothing there try google for a wiring diagram. Those stock lift pumps suck!