Is lift pump failing or sucking air
 

Fuel pressure gauge acting funny last couple days. At start-up reads 16psi drive down the road stays the same, back out of the pedal, coasting or light pedal psi drops to 8, back on the pedal back up to 15. Is my LP failing, is it sucking air. or is my releif valve on VP failing. what do you guys think I have another LP to put on it, but I haven't heard of anybody getting more psi when more pedal is applied.

JED

LP is toast. Mine was doing the same thing. It was dropping to 4/5, I would "pop" the pedal and it would return. I replaced it with a FASS II and haven't had the problem again. You could check for leaks first, but it's probably the LP.

Just the torque of the engine is enough to "wiggle" the rubber fuel line. Put a couple of 89 cent clamps on the transition from rubber to steel. Cheap enough and it might fix your problem. It did mine. Was going to chuck the pump a couple of thousand mile ago and it is running perfect now

I tighened connections at the tank and the lift pump,seammed good took apart and cleaned,tried different lift pump that one didn't work at all,it was old one I took off last summer. changed the relief valve on VP return line no help. I guess i'll buy me a new lift pump now
JED

Mine did the same thing with a new lift pump. The truck ran fine and probably would have for longer but I did no know if it was good or bad. If you have a tapped banjo like I did it will do that. The Injection pump seems to flow fuel when you let off the gas to cool itself. Well I bought the fass because I am planning some injectors and a box and want to do it right the first time. With the fass the 0-15 psi gauge is useless. When I start the truck it pegs 15 psi and never moves. I would say you are fine. You can do the flow test to confirm if the pump is okay. If you have the $$$ buy the fass and never look back.