Engine/Transmission (1998.5 - 2002) New lift pump, what are acceptable pressures?

[concrete-steve]

Ok, so today I installed my new lift pump from Cummins. My 2000 has 123K on it and the lift pump had no pressure, but you could hear it run (so who knows how long it was like this). I just installed my fuel pressure gauge on Saturday which told me the pump had no pressure, but the truck ran fine up until this point. The electric pressure sender is hooked into the schrader fitting on the injector pump. No mods to the motor, just gauges and high flow air filter.



The fuel pressure with the new lift pump at idle is 15psi. Slightly off idle and up to 1500 rpm, the pressure drops steadily and once you are above 1500 rpm and starting to step into it harder the pressure goes to zero (actually slightly below). Needless to say, at wide open trottle there is no pressure.



Do you think I got a bad lift pump, or could it be something else? Is this something the Cummins dealer should replace without question?

 

[ABossana]

i have 98k miles on my stock lift pump,

Idle: 16psi

crusing @ 65mph: 14psi

WOT: 11-12psi



i would say your numbers are low, possibly a bad sending unit?, sending unit location?



Anthony

 

[concrete-steve]

The sending unit is hooked into the schrader fitting at the injector pump. Could be the sending unit, but it reads 15psi at idle consistently.

 

[lcoblentz]

This may be obvious, and I'm not trying to offend you in any way! Have you tried replacing the fuel filter?

 

[Jefff929]

This may be obvious, and I'm not trying to offend you in any way! Have you tried replacing the fuel filter?

reasonable question

 

[24V-DSL]

I'm assuming this is an Autometer electric? Move the sender away from the engine... . they don't like vibration. Call autometer tech and they can give you a source for a snubber, as well. Both my snubber and sender are mounted on the driver's side inner fender at the fuse box area.

 

[Schlickenmeyer]

Just put in a new pump, 12. 6 avg idle (saw 13 once, briefly). I can pull it down below 10 with moderate throttle, but it is kinda cold in MN now, and I'm sure that does not help. When the truck warms up the psi goes up by at least a pound. Starting in the cold around 10. 5 to 11. 5.

 

[concrete-steve]

I didn't post all the information. All this started with a filter change on Saturday. Then I moved onto installing the gauge and sender. The gauge and sender are from Westach. The needle is very responsive to throttle position and load but does not vibrate around at all. I'll try moving it away with a rubber hose to see if this will make any difference.

 

[nps]

Sounds like a bad pump or a marginal unseat of the schrader valve. Three choices to verify:



1. Give the connection to the schrader valve another 1/4 turn and see if the pressure changes.

2. Put your sender on the schrader going into the filter housing and see if your reading changes.

3. Get a mech gauge and tape it to your windshield and observe the mech gauge while driving.

 

[easleyj1]

I Have had loads of trouble from my electric Westach FP gauge and ended up replacing it with a mechanical. Many here run them for years no problem so go figure. When I was having problems I went to Autozone and bought their cheapest mechanical oil pressure gauge to verify my readings. It was a handy 16. 00 purchase and confirmed that once again my sender was bad.



Jonny

 

[concrete-steve]

Thanks for all the input guys. It appears that the sender being connected directly onto the schrader fitting is the problem. I purchased a 12" grease gun whip hose and mounted the sender onto the end and suspended it with tie wraps temporarily. Now I read 15psi and idle, 12-13 psi at cruise and 10 psi at WOT.



I checked the installation instructions and nowhere could I find this information, in fact the actual information reads "install sender into medium to be measured. Connect base of sender to a good engine ground" Go figure... .



Great information from everyone, thanks TDR!!!!!