Engine/Transmission (1998.5 - 2002) Low fuel pressure

[JonWilson]

I am trying to figure out a problem on a friend of mines truck 2001 cummins

and it keeps lighting his low fuel pressure warning light. we have replaced the lift pump twice and relocated the pump to the frame close to the tank to make it a pusher. still had problem ,bought a draw straw and complete big line kit and installed these and still a problem we tried different senders for the light, still have problem vehicle runs beatifully and has a lot of power especially after the draw straw install but that light is bothering us any other ideas would be appreciated we plan on a gauge this next week but we also figured that trying different sender units would have made a difference all to no avail though. thanks in advance. add on i would think with different light sender units something would have changed if the pressure were there.

 

[SnoKing]

He needs a fuel pressure gauge. My stock pump on the frame rail idles at around 15, cruise at 12-13, and WOT at 11. Stock pickup. Might swap the fuel pump relay with another relay. SNOKING

 

[ESheffield]

I just joined here for precisely the same problem! Got my truck (2002 Ram 2500) in early June and installed FP gauge first thing. No mods. Had 14 at idle, 8 WOT. About a month ago it suddenly dropped to 8 at idle, 4 or less WOT (never 0 though). Kind of popped between 8 and 14 for a while, often could get it to go up by revving the engine a bit, but finally stuck at 8. I thought the FP was going out. Installed a BD Diesel relocated lift pump - no help. Confirmed readings with another gauge too. Posted on another forum and a suggestion there was to install a piece of clear tubing at the injector pump and watch for bubbles, and if any showed up keep moving it back in the system to isolate a possible air leak. But I didn't see any.

I did notice that if I brake hard the pressure will briefly come up a couple of PSI. Not sure if that's meaningful or not though.

I just happened to remember that after installing the new pump I checked the voltage while running and it was right at 12. Typically I would have expected closer to 13. 8 or so. The relay comment made me think about that. Again, don't know if that's significant.

Eddie

 

[NHelmer]

Mine started doing the same. Thought it was the fuel filter so I swapped it out worked good for about 2-3 weeks. Now back to fluctuating. Sometimes it drops during lock up sometimes it goes up or stays put. Also whom ever can shed some light on the FP going up during braking would be a god, mines been doing that for about a year now. BTW not sure if it's in my sig or not but I have the Holley blue. Could bio be causing my problems? I only run 5% I think.

 

[rweis]

GENERALLY SPEAKING what seems to work is really significant volume at 14 psi - 16 psi like a Walbro, FASS, RASP, whatever mounted down on the frame area over by the tank so the pump does not have to suck much of a verticle lift.



Once you have significant volume, in the right psi range then something like a mechanical bypass valve pretty close to the VP44 inlet shunting the excess fuel back to the tank. The bypass valve will controll the psi.



If you go back and read the hundreds of miles of lp threads and step back and say "what is different then vs now"?, it seems to be massive quantity (not matched quantity) at the right psi with the excess shunted back to the tank.



Then there are threads on fuel cooling, ultra filtering, etc to add to the mix.



Bob Weis

 

[NHelmer]

ok my sig. does tell about my supply system. Btw the "cat" filter assembly is off a 345CL excavator with a 3406E engine that cranks out in the neighborhood of 450hp. I still don't have a draw straw but over all I would assume my flows pretty damn good for what I have. I could be wrong though (or so I'm told by my wife all the time). Keep the ideas coming.