bigragu

Hey all me again. Now that I am able to have spare time to chisel away at lingering items on my truck I can finally address the plunger lp I installed on the truck back say in 2007 when "it was the desirable upgrade to do" at the time. Bought all parts from Cummins West. My outstanding question on this is the reading I am getting on my fuel pressure gage. Autometer electric type, with snubber. I am floating at around 18 psi at freeway cruise speeds and it will drop to around 15 psi at wot up a grade. Is this normal? Reason I ask is after I installed the pump a couple of years go by and then I started reading about certain spring rates in these plunger type lift pumps. I pulled all part numbers from the sticky and back then there was no notice on spring tension differences. Am I correct in thinking maybe I got one with the wrong spring? If so, I'd rather not worry about the trouble of disassembly and possible leaks, that is unless it would be detrimental to my injection pump. Please advise

thrashingcows

18 psi is getting close to what the front seal on these IP with take before they fail. I have heard that 15 psi is the safe number....but maybe others who are more knowledgeable then I will chime in on this.

But regardless the higher pressures will not harm anything. In fact it's better for the whole system, IP too, to have all the fuel it needs without starving for it during hard pulls or WOT runs.

cougar

Yes, 18 is risky without modifications. 15 is fine, 7 is stock. As long as you have some left over lift pump pressure at WOT, the VE will run fine with it.

Dean Snow

Mine runs 18 to 20 auto meter snubbed at idle. Crushing is 15ish and wot is 2-6psi. That's with 3/8 line from draw straw to IP. In your case I'd say it's normal

BearKiller

I have read that 20-PSI is the maximum sustained limit for the VE seals.

All of the gauges on our trucks are analog mechanical with McMaster-CARR snubbers; the fuel line also goes straight to the gauge.

That being said, on my F-350, gauging between the filter and I-P, with 3/8" rubber lines and 06-JIC/AN fittings, my 4944714/3936320 genuine made-in-USA Carter straight across the Cummins parts counter piston-lift-pump idles between 12- and 16-PSI, depending on ambient temperature.

It sometimes pulls down to 10-PSI if I don't shift down when I should.

I seldom see the gauge above 16-PSI.

This is a Stewart-Warner gauge.

Have you ever checked your electric gauge's readings against a mechanical's ??


There is a newer Cummins number = 4988751 --- not certain if this is a genuine Carter or a Delphi --- Cummins has used both --- the Delphi has the inlet and primer positions reversed.

You have to be careful when cross-referencing numbers; you may think you are getting a USA Carter and end up with a foreign Delphi.

Just recently, I saw a DIAPHRAGM pump, new-in-the-Cummins-box, with #3936320 boldly printed on the flaps.



For what it's worth, the listed specifications for all of these pumps, whether piston or diaphragm, show the OUTLET as 14mmX1.5 and the INLET as plain old 1/4-NPT.

When I didn't know any better, I have successfully used 1/4-NPT for the outlet, but it is tricky to get the tapered male NPT threads to properly seal in the straight-cut metric female orifice.

The 1/4-NPT will easily thread into the metric outlet and the 14mmX1.5 easily threads into the 1/4-NPT inlet.

bigragu

Thanks TC. Will look into comparing to a mechanical fp gage

BearKiller

Many is the un-knowing soul who has driven a VE-equipped engine for months, nee years, up hill and dale, with a dead diaphragm lift-pump and been nary the wiser. In many agricultural and industrial applications, no lift-pump whatsoever is used.

It would be interesting to see a comparison of idle-speed pump case pressure with no lift-pump, a diaphragm lift-pump, and a low-pressure piston lift-pump.