Engine/Transmission (1998.5 - 2002) vp44 or lift pump??

[SCox]

Replaced lift pump last week, still have a rough idle intermittently, and after a long drive idles rough and goes into limp mode once I turn the truck off. Checked pmax wires, none loose. I'am totally lost at this point. How can I make a temporary pressure gauge to test my lift pumps pressure? Can a bad lift pump cause a rough idle?? How do I know if my VP44 is bad?



totally frustrated and confused

Steve

 

[RRFinch]

I recently lost the vp44 due to lift pump failure. It took several months for the 44 to fail. During that time I had some interesting and puzzling symptoms that I suspect are related:

1. Reduced, and variable, exhaust brake pressure. I "think" this may have been due to reduced injector pressure which caused late firing and reduced exhaust pressure. Exhaust pressure is used, along with vacuum, to actuate the brake.

2. Somewhat reduced power... . Subjective evaluation.

3. Engine, in the later stages, would mommentarily cut out.

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You can attach a pressure gauge directly to the output 1/4" NPT fitting on top of the fuel filter. That will give you pressure out to the vp44. From reading other posts, and dodge mechanic, it should be at least above 10 lbs at idle.

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You didn't state why you replaced the lift pump. If it produces low pressure (below 10 lbs at idle) I am told it can make the 44 work harder. This makes the pump in the 44 work harder and it eventually fails.

 

[Briar Hopper]

Steve, your 2001 has two fuel pressure test ports on the system. One is right on the side of the injection pump, the other is behind the fuel filter housing. We make and sell a test gauge that fastens to these test ports, as well as furnish test port fittings for the 98. 5 - 99 trucks that only have plugs on top of the fuel filter housing.

Your rough idle sounds suspiciously like air getting into the system somewhere. Maybe a loose or leaking banjo bolt?

Try removing the MAP sensor connector for the powermax, reconnecting the stock wires, turn off powermax, and drive the truck.

Check for fuel leaks at the banjo bolts, especially the fuel return line.

On my own 2001, I had a rough idle and a loss of power until I replaced the MAP sensor with a new one.

 

[highland]

I have experienced rough idle on occasion, as well. Just replaced lift pump second time (130k). Dealer said pump was still working, but inconsistent/low pressure. I still get rough idle sometimes. Additives, injector cleaner (BG44K), different fuel does not seem to clear it up. The last few days, however, it has run perfect. Just do not know what the deal is here. Help?



99 QC 4x4, Horton Fan, Otherwise stock. 135K miles.

 

[SCox]

Thanks guys for the responses,



I took the TST off this evening, took out the map piggy back. I then went for a 40 mile drive, truck ran perfectly with no rough idle or check engine light. Real test is tomorrow, I'll be towing 10k for about 25 miles. With the tst on this would give me a rough idle then limp mode. I Think my map sensor is malfunctioning or my TST has issues. Rod at wildcat seems to think something might be up with TST, he said he will gladly exchange it if I pass my towing test tomorrow, great guy.



About the rough idle, I read through about 5 pages last night under "rough idle" search. Things that came up consistantly were problems with injectors, vp problems, few comp box problems, couple map sensor problems but never related to lift pump problems.



On a good note, I found someone with a mechanical fp gauge finally.



anyways, more tomorrow

SteveOo.