Engine/Transmission (1998.5 - 2002) Internal 'lift pump' inside the VP-44?

[HoleshotHolset]

This may have been covered before, and if it has... . my bad!



The subject says it all, but is there an internal 'lift pump' inside the VP44? The reason I ask this is that some people are seeing 0psi on thier FP gauges (with the sender installed post filter, right at the inlet of the VP44)... yet the truck still runs.



Another reason I ask this is that the VW TDI's use a VP37 (?) which is sorta like the wicked step sister of the VP44... . and it has an internal lift pump and no other fuel pumps of any kind.



I know I'm not really comparing apples to apples... . but the movement of the cider is pretty important.



Just curious...



Matt

 

[E7mack96]

Just a thought

in my opinion, 0 psi is not necessarily a bad thing. It just means that the vp is using as much as the supply is delivering.



What would be interesting to see...



Is there a vacuum developed at the inlet to the vp from less than ideal amounts of fuel. now That would be a concern.

 

[KLockliear]

Originally posted by HoleshotHolset

is there an internal 'lift pump' inside the VP44?Matt

Yes.

 

[HVAC]

Yes

There is a sliding vane style pump in the front of the VP44

 

[Rammin On]

I don't think I'd actually call it a lift pump ... the vane pump is the low pressure stage to supply fuel to the radial piston pump which is the high pressure stage.

 

[HoleshotHolset]

Cool... . thanks for all the replies.



The VW TDI doesn't need any other pump than what is inside the VP37... . but they're only 10' long and the fuel tank isn't much lower than the pump.



These big-honkin' Dodges need a secondary lift pump to handle the height above the tank and the length of the truck.



So... in theory I could put an injection pump off a B3. 9 (VP44 variant) onto a little TDI and blow it to bits!! Cool!



Matt

 

[Snow man]

The internal pift pump will suck the fuel into a vacuum,mine did when the stock lift pump was weak,it could get -3psi of vacuum on the SPA guage on 5x5,and level 3 would bottom the guage at 0 perfectly,no poressure,no vacuum at wide open.

 

[Lsfarm]

0 Psi??

Matt, I would be seriously concerned about the life expectancy of a VP that has been run with no lift pump pressure.



The 'extra' pressure being fed to the VP is used for cooling and lubrication.



Steve StLaurent ran his truck with a five gallon can for a fuel tank, and the fuel temperature rose from ambient of 55* to 105* in only twenty miles of driving. So the VP is definitely in need of extra fuel for cooling.



All high pressure fuel pumps need positive pressure so that they don't get air bubbles in the fuel caused by cavitation. This is why the VP has the little pre-pump to feed the high pressure portion of the pump.



In our aviation injection pumps if the pre pump fails or if there is any loss of positive fuel pressure, the injection pump has to be tested for damage.



So yes there is a small pre-pump in the VP, but we need our infamous lift pump too.



Greg L. The Noise Nazi

 

[RobbyRam]

Can someone post a picture or drawing of a VP 44's internal workings?

 

[Ncostello]

A good man sent me here once...

This was passed onto me by Steve St. Laurent. Good reading. After you read all that, you will get the opinion that either it works or it dont. Impossible for even a good mechanic to trouble shoot. Just my opinion. There is also some real good photos and diagrams on dodgeram.org. And a real good explanation of how it works.



But I must warn you, no where did I ever read where anyone said the VP had and internal lift pump per se. I dont think you'll find verbage to that effect. It is worth reading to draw your own conclusions. VP 44 information



Go to page 4 for some photos of its internals.



I dont know exactly where on dodgeram.org I saw the VP drawings cause I stumbled upon it by searching on google under "VP-44 injection pump" I think. But it was something pretty good for showing cut aways etc.

 

[Ncostello]

Here it is. I liked this one.



VP 44 link

 

[Groover]

I have been pondering the lift pump problem lately as I finally got a gauge post filter and numbers are - 8psi idle, 5 psi cruise, 2psi WOT. I think cummins says no less than 2psi at any time. Am I ok?



The Lift pump runs at a set speed and pumps a certain amount of fuel which is not going to change much. The internal pump in the VP44 is RPM dependant. Highest lift pump pressure should be at idle (no-brainer). The whole issue with the lift pump appears to be lubrication and cooling provided by the fuel as it passes through the injector pump.



Somebody correct me if I am wrong but there is a overflow valve after the vp44 internal fuel pump that is set to open and return fuel to the tank at 12-14psi? As engine RPM increases the internal pump (vp44) is turning faster and should produce more volume of fuel to the vp44 or to the return line. The engine is turning faster, the vp44 is turning faster - lift pump still pumping same amount. It seems that the internal pump is "out-running" the lift pump and post filter/pre vp44 FP drops accordingly. Is this bad? Maybe not - to a point. Even with say 2psi lift pump pressure isn't the internal pump still pumping greater than the return valve pressure and flowing quite a bit of fuel both through the pump and injectors and returning a substantial amount of fuel to the fuel tank? All this flow through the injector pump should cool and lubricate the pump regardless of what the lift pump pressure is.



All I am saying is that reason would dictate that any positive pressure from the lift pump should be ok. The vp-44 is used in other applications without a lift pump.



Seems that 14psi is what everyone is worried about as that is where the overflow is supposed to open and provide "extra" fuel flow for cooling.



Just because the FP gauge after the filter does not show 14psi does not mean that fuel inside the vp-44 after the internal pump is not opening the overflow valve and cooling/lubricating.



If we are worried about cooling of the pump by fuel we should never let the tank get below 1/4 or so. I don't know about these trucks but the older ford fuel tanks would get real hot when near empty (navistar 6. 9 diesel).



If I am full of it please tell me. But say it nice PLEASE!

 

[Lsfarm]

Pressures too Low

Groover, DC says 10 psi idle, no less than 8psi at WOT.



The 14psi is what most new lift pumps provide, and this pressure is needed as you said for cooling and lubrication.



But having just enough to provide positive pressure is not enough to to cool and lubricate the VP.



Even cheapo DC says 8psi is a minimum, so if this is the lower limit for warrantee on a lift pump, I'm sure it IS the lower limit. DC doesn't want to spend any $ it doesn't have to!



Replace your pump, or add a pusher pump back at the tank, you are running on borowed time.



Greg L

 

[Snow man]

Groover,your lift pump is real weak,5 psi cruising,it wont last long,i would change it now.

 

[Groover]

Anybody know where DC says 8psi minimum. If someone could provide a link to this info. Have searched dodgeram.org etc and can not find any pressure specifications. Just to be on the safe side I would like to get my lift pump replaced and see better fuel pressure but am still not convinced that 5 psi after fuel filter is going to cause my vp-44 to self destruct.



Great Topic: Appreciate all the info available on this website



I think I was told (in a nice way) that I am full of it. And maybe I am.



Thanks

 

[JR2]

Groover - trust us... you need a new one.



I don't know where the actual # is, one of the guys on here is a DC Tech (thats is handle too) and I believe it was him that posted the new info from the DC Star hotline.





JR2 15psi at idle and loving it.

 

[Roger rodbolt]

My information also came from the Star Hotline as JR2 mentioned 8lbs minimum - any operationing condition. That is on a stock engine making 200hp or less at the rear wheels.



Not trying to stir or be impolite but why, when it is a known fact, that our fuel system is marginal on a stock truck in new condition, would anyone want to tempt fate and not run strong fuel pressure? A bombed truck needs more fuel and no knowledgable person that I know of will tell you that stock psi or higher then stock pressure will do any harm- 15, 20lbs or even a little more is good insurance and may improve performance. A higher flow system (lines, filter etc) with extra volume, doesn't need as much psi but few folks spend the bucks to do that. I've seen electric fuel pressure gauges that would register normal pressure for a few seconds (on acceleration) and a mechanical vacumn/pressure gauge on the same, would show as much as 5 inches of vacumn IMMEDIATELY when the throttle is punched. I have a low pressure warning message on my Blue Chip FMS that comes on below 4 or 5lbs of pressure. If I shut off my pusher pump, the warning will flash immediately with light acceleration, while my mechanical gauge (that is highly dampened with snubber and needle valve) is still registering 8-10lbs. (This truck is heavily fuel even without the electronic enhancements)



I believe that most of our engines would last for a good while on 10lbs of engine OIL pressure but I'd much rather have 50... Okay I'll get off my soapbox now . Larry (trying to improve the reputation of our beloved VP 44)

 

[Lsfarm]

Search Lift pump

Do a search on lift pump, you will have about a month of reading.



When you take your truck in for a lift pump under warrantee, the 'tech' will take readings, then have to call the 'STAR' hotline to get an approval to either order a replacement pump or not. the 'STAR' pressure guidelines are the ones used here. [10psi idle, 8psi WOT]



DC has finally realized that the VP is more expensive than the lift pump, and to replace the lift pump when it is not providing enough extra fuel to lube and cool the VP



The STAR line person will also ask the tech if there are any modifications on the truck so they have an excuse to void your warrantee. [been there]



Change your pump, unless you like gambling! This has been discussed untill the cows have come home hundreds of times. Keep a good lift pump feeding your VP or expect to replace the VP [quite possibly out of your own pocket]



Greg L