I think my lift pump may have a problem at 50,000 miles. Driving down the road today the after filter pressure gauge reads 4 PSI. I go back home and check the pressure with another mechanical gauge on the injector pump and again 3-4 PSI at idle. I’ve read several threads on lift pumps and don’t remember reading about a pump with the same symptoms as mine. When the engine starts the FP gauge jumps to 12-13 lbs as it normally would, five to ten seconds later the gauge drops to 4-5 lbs at idle. Shut the engine off and restart and the same 12-13 lbs and then drop to 4-5 lbs in a few seconds. Fuel filter was changed about 5000 miles ago and I can’t believe this problem could be filter related. I always check the gauges whenever I drive the truck and today is the first time the truck has ever had < 12 lbs fuel pressure at idle. Could this be some problem other than the lift pump?

 

I would change out the filter, and recheck it. Sure sounds like a bad LP to me. My previous Carter LP would do the same thing.

On start up, my Holley will spike a little at first (warm start), and then settle in several pounds less at idle.

Matt

 

I think the lift pump is well on the way out. Be sure you clean the filter housing out when you put a new filter in. The guts of the lift pump can be in the filter housing.
If you have a test gage you can test the pressure drop across the filter by using the 2 plugs on the top of the filter housing.

I change filter at 2 psi drop...about 8k miles

bentwings

 

Hey, I have had the same problem with the same gauge. I redid all my connections so that problem is ruled out. The stupid thing is today the gauge reads 15psi. at idle and 10psi WOT. Mine would drop like yours after about 5-10 seconds to 3-4 psi. at idle then 0 as you would accelerate. I'm curious too, no electronic fuel mods or injectors, just bigger banjo bolts. Also fresh fuel filter. Could there possibly be air getting into the system. Help, if its the lift pump I'm ready for a belt drive now so I can make this dog hump.

 

Air getting in the system will not change the pressure reading unless it is before the pump and will not let it prime.

 

Could this be a tell tale sign that the pump is slowly on its way out? I have read other threads about intermittent pressures and how the lift pump would fail. Thanks again.