Engine/Transmission (1998.5 - 2002) Fuel Pressure

[MRiley]

I'm Trying to figure out what is normal here. I just got my gages installed (egt, boost, pressure) and I've noticed my pressure gage seems to drop more that I expected. Normal cruising gets me about 10 - 12 psi. But when I really jump on it and push through the gears the pressure drops to 6 - 8 psi. Long highway pulls get me down to 8 psi or less too. Is this norm or is it a sign of bad things to come?

 

[darkhorse]

That's pretty normal.

 

[MVieira]

MRiley,

I wondered the same thing. I put my Di-Pricol gauges in over a year ago and the first thing I noticed was the fuel pressure was about 13 to 13. 5 psi at idle, 10 to 11 psi crusing at 65 mph, and when I floored it it would drop to 7 to 8 psi instantly and if I kept my foot in it, it would keep dropping past 5 psi to 2 or 3 psi before I'd get scared and let up on the pedal, ( 105 to 110 mph). I then plumbed in one of my liquid filled 0 to 50 psi gauges I used to use when I was a mechanic for the CAT dealer I work for and I got almost exactly the same pressures. I felt I had low numbers compared to what I've seen most people post so I went to Cummins West and bought a new lift pump and installed it. Guess what, same exact pressures, only thing I noticed was when I floored it, it didn't drop as fast and it held to 5 psi alittle longer, but I can still see it drop below 5 psi if I keep it floored. So I guess that is the way it is. My truck only had 12,000 miles at the time. I've got 23,000 miles now and I haven't seen any drop in psi and now I have a spare lift pump. I also kind of wondered if a long bed truck may see a lower psi from the lift pump than a short bed, is the fuel tank closer to the engine on a short bed ? Less distance for that little vane electric pump, that's mounted higher than the fuel tank, to draw from ? I'd like to know if anyone has any input on this. I've only got an edge ez but I'm convinced I'll have to do some upgrade to the lift pump before I add larger injectors down the road.

Mike

 

[keimmmo]

I have moved the factory lift pump back just ahead of the tank. It didn't help max pressure, but it seemed to help a little on the minimum side. I am still stock, but I can not pull the pressure below 5 no matter how long I have the throttle down.



A couple of thoughts. I live 6,000 feet above sea level. When I get down near sea level my fuel pressure goes up right at 2 psi across the board. I have observed this on two pumps over a period of 60,000 miles. Also, all pressures drop except the max pressure with the motor off when a filter starts to plug. I run my filters until I get about a 2 psi drop in pressures and change them.



Good pressures give bragging rights, but I do not believe they are needed. I have read everything I could find on how pressures affect injection pump life. My conclusion is that you will not damage the pump as long as you have positive pressure... even if it is low. You need to maintain a 5 psi minimum for the timing advance to work in the injection pump at cruise, but it will not advance at full throttle, so slightly less at full throttle would not hurt anything.



Steve