Engine/Transmission (1994 - 1998) High Fuel Pressure?

[Hummin Cummins]

Hi,



Tested my fuel pressure today because I have been having a lope at an idle and ticking from what sounds like the lift pump area. To my suprise, I had 38 psi at an idle and 41-42 psi at 2000 rpm and WOT. At first I thought it was the gauge, so I swapped it out and still had the same readings. I assumed that fuel pressure would drop as rpm increased. I'm going to order an overflow valve tomorrow just for giggles. After my searches I'm guessing that it is stuck because when I pinch off the return line the idle doesnt change. I also cracked each injector line and they all seem to be working. Idle got rough with each line that I cracked. FYI there is 206000 miles on my truck. Any other ideas about the lope?... . timing maybe? Sometimes it sounds like a miss coming from the stacks at high rpms, but no white / blue smoke. The lope seems to be more noticeable after the truck has sat for a few hours..... Air leak? Power seems good (but you can never have enough) and mileage is ok too.



Chris

 

[Missouri Mule]

If there is no load on engine the fuel pressure will climb yours seem to be a little high but higher is better than lower.

 

[DieselDoghouse]

A ticking like a bomb could be early sign the lift pump is loosing displacement. Noise apparently comes from a weakening return spring and the piston not following the pushrod on the downstroke. I'm sure you got good readings at idle, I wonder what they are at road speed - when fuel demand goes up the pump may not be meeting it. If you're losing top end I would be suspicious the pump is geriatric. Just my experience.

 

[Matthug]

Sounds like you have a restriction in your return line somewhere post injection pump. Isn't there a filter for the return line before it goes back into the tank? Can't remember if I saw a thread on that before or not.

Anyway, I just replaced my lift pump and overflow valve couple weeks ago. Before I had 10 PSI at idle and 26 PSI at 2000 RPM (suppose to be 22 and 28). I have 24-25 PSI at idle and 34-35 PSI at 2000 RPM. The overflow valve is from PDR and I think it's meant to give it some more pressure than stock.

 

[Hummin Cummins]

So I guess my first step is to replace the overflow valve and take pressures again. I'm betting that they will drop below specs once the overflow is working correctly. I need to add another section of hose so I can read pressures while under load. Really would be no pity for the lift pump or the overflow considering the mileage they have on them.