Engine/Transmission (1998.5 - 2002) Lift pump pressure swing on 98.5.

[RRounsavall]

Checked my pressure and it was swinging from 15 to 5 psi. It would stay at 15 for about 5 seconds and drop to 5 for about 5 seconds this is at idle speed, pressure stayed at 15 psi at high idle. This is after filter change. Is this normal or is the lift pump going bad.

 

[ThrottleJockey]

Might as well change it out. I'd rather change out a lift pump than my injection pump, right?

 

[rjrkihap]

This is how all of mine (4) began to fail. Pretty soon it will stay at 5 PSI for longer and longer until it finally fails completely. I would suggest changing it sooner than later. I'd also strongly suggest upgrading to something more substantial than the factory lift pump (FASS, FASS HPFP, FASS DRLP, AIR DOG,etc. )

Good Luck

Ron

 

[fox]

Put a REAL pump on it!!!

 

[JLandry]

Checked my pressure and it was swinging from 15 to 5 psi. It would stay at 15 for about 5 seconds and drop to 5 for about 5 seconds this is at idle speed, pressure stayed at 15 psi at high idle. This is after filter change. Is this normal or is the lift pump going bad.

If this behavior happened in the first few minutes after changing the fuel filter, then it was probably caused by air being forced out of the filter housing. The pressure reading should stabilize within a few minutes of engine running and after several restarts. If the pressure doesn't stabilize, as others have said then it could strongly indicate a problem with the lift pump... or it could be a faulty pressure gauge.



One way to eliminate most of the air from the filter housing after changing the element is to activate the lift pump 3 times in a row before starting the engine for the first time. This is done by turning the ignition key on, briefly bumping the starter (but NOT starting the engine), and leaving the ignition key on. This will cause the lift pump to activate and continue running for approx. 25 seconds. You should hear it and see the pressure on your gauge.



Good luck,



John L.

 

[Moe]

My gauge has plenty of pressure at idle(12lbs) but has an annoying vibration of the needle all the time. Does the line need bled at the gauge? No codes yet. Thanks, Moe. Sorry guys, not trying to hijack thread, just wondering about these pumps

 

[JLandry]

My gauge has plenty of pressure at idle(12lbs) but has an annoying vibration of the needle all the time. Does the line need bled at the gauge?

Moe,





If it's rapid, I doubt the bouncing you're seeing is casued by the lift pump. More than likely you're seeing pulse waves from the fuel injection pump. You should try check the fuel pressure behaviour using a different gauge (an inexpensive pressure test gauge).



A little story...



My mechanical fuel pressure gauge had an annoying buzz at certain engine rpms when under load and I could see the gauge needle vibrating rapidly a tiny bit. In fiddling with the gauge, wires, and plastic line, I found the sound was actually coming from the plastic line located behind the gauge.



Unbeknownst to me I had a very slow seep (leak) in the plastic line at the isolator. One day the gauge gradually went to zero over about a minute or so while I was driving and it stayed there... it nearly gave me a heart attack! I quickly verified the fuel pressure was good using a second test gauge and found out the cause of the faulty reading in the truck was all of the anti-freeze had leaked out of the plastic line leading to the gauge. I fixed the leak, re-centered the diaphragm located inside the isolator and refilled the plastic line with antifreeze. The gauge (or the plastic line to the gauge) has never buzzed again since!



So, my answer to your question is a firm *maybe*! Maybe bleeding the air out of the plastic line leading to the Gauge and re-centering the diaphragm in the isolator will eliminated the needle bounce. Or maybe not because I've read here on the forum some people have had to installing a "snubber" in-line between the injection pump and isolator to smooth out the reading.



Regards,



John L.

 

[RRounsavall]

lift pump pressure

Thanks for all the info, after driving it to town and back the pressure has stabalized at 15 psi on the filter outlet. Again thanks for all the help.