Engine/Transmission (1998.5 - 2002) Please help with mystery fuel delivery problem

[Arcticat]

I'm trying to track down the source of my 0 fuel pressure problem. So far I have replaced the fuel filter and lift pump. The filter was clean and the fuel was not jelled. The truck starts but runs rough when the pressure drops to zero, and runs fine when the pressure is fluctuating between 1-3 psi. Here's the odd part - if I bump the engine to run the lift pump on it's own, I can hear it running normally, and it pumps 15psi as normal. I opened the filter canister drain and it was pumping a fair volume. For some reason it is either not operating or operating at only part capacity when the engine is running. Ideas? I'll do anything to avoid taking it to the dealer. I actually think I know more about this engine than their diesel mechanic. Thanks

 

[Whitmore]

Sounds electrical to me, at first when you just turn the key on it is supposed to run at half power , mine will spike up to about 6-7 psi and then when you bump the starter or start the truck it is at full power and should give 15psi. It sounds to me that when you bump the starter and get that 15 psi that the fuel pump is OK so I am wondering if you got a pigtail from Cummins and tried an alternative electrical source to the L/P you may prove the system OK, another thing I would check is the relay and its integrity of the connections



cheers, Kevin

 

[KenHokie]

I agree, it sounds electrical to me also. According to my '01 service manual, the LP is connected directly to pins 15 & 35 of the ECM. The wires are Yellow/White color coded (at least on an '01). I'd recommend disconnecting the plug on the LP and checking the voltage from the ECM. The Black/White wire should connect to GND. Another test would be remove the plug on the LP and connect +12V and GND directly to the LP. If you get ~15PSI, the LP is good. Maybe you have a bad ECM??:{ Good Luck!

 

[fox]

Just a thought, is there a restriction in the tank that is moving around?

A few months ago my 02 would loose pressure while driving so I would stop and restart it. It would then be fine for a few miles until I would slow at a light, then the problem resurfaced. Normal pressure was 13-17lbs. when it dropped it would go to 1-3 lbs.

After some testing and thinking, I decided to go to the tank and start there. Good guess, as I found the pick-up screen blocked with lint/hair/largeclumps of ? . Cleaned it up and it has been fine since. Either I got a bad load of fuel or I have a 'freind who needs his body adjusted' .

Another truck that I have developed a low pressure problem and it was the algea plugging the pick-up screen. It was so bad that it took about 50lbs pressure reverse fed to the tank to blow it loose. ( from the filter to the tank. ) Then I added some biocide and it hasn't been back. We drove it several tanks and then drained it looking for lint/ hair etc, but it was clean.