PJveetwin

So my 99 24 valve has 160K miles, around 50K on a rebuilt VP44. I'm running a AirDog FP 100 lift pump with a Isspro fuel gauge inside the cab and has always held 15 psi. So I'm in a very remote area of the Mojave desert and I see my FP drop to 0. I stop and make all the normal checks, with no luck. no voltage to the pump. I made the maybe poor decision to drive it homes as recruiting help was not really an option, aprox 160 miles. The next day I'm able to verify it's the relay in the airdog and replaced it. FP back up to 15 psi. Starts normal, no codes and is running fine, then as it starts coming up to operating temp, around 140 degrees, I see pressure start to slowly drop to eventually 4 or so, but seems to still be running fine. Airdog still has full voltage at the pump. Did a full cool down several times with the same results. Changing the fuel filter didn't help, I now thought the VP44 bypass valve could be at fault, so I capped off the feed line to the VP44 after the gauge to verify actual pump pressure, figured out I could jump the plug for the relay and manually run the pump, something I could have tried on the side of the road....... a lesson learned. So pump pressure was still the same. Disassembled the gerotor in the pump and the pressure relief valve, all looked good, then swapped out a different gauge, no change. Then after I installed the original gauge back in, it came back to 15 psi, and worked as designed for multiple cool down's and starts. I'm assuming something was in the hose?? So bottom line here is, I'm not an expert by any means, just a normal owner and did the basic trouble shooting and It appears I cheated death and the VP44 continues to live.

jrs_dodge_diesel

Check your wiring to the lift pump from the wire harness. I had odd pressure issues too until it went to 0 for good. Thought the power circuit in the ECM for the fuel pump died. Went to salvage the connector to wire in an external really and this is what I found:




The nick on the black wire was from me snipping it to repair, before I thought to take a picture. For the lift pump, the black wire is the ground, yellow is positive. The yellow wire started to chafe over time and finally wore through, causing my problem.

I patched the damage and spliced in a few extra inches of wire and my pressure has been solid ever since. Check your wires, you may have a similar problem.

PJveetwin

Thanks JRS for the suggestion, but my problem has been resolved. I mainly shared my scenario here to assist other owners in case they have a similar situation.