Engine/Transmission (1998.5 - 2002) LP pressure requirement from Cummins /

[Tractorat]

I sent a message to Cummins asking just what the minimum psi should be at the VP. Below is the answer that I got. Can this be right ?



Summary: Low Pressure Light



Solution:



Zero is the minimum pressure we want to see. In many applications of

the VP44 pump there is no lift pump and the injection pump must suck the

fuel through the filter.



The light comming on at a nominal 3. 5 psi gives some warning above the

minimum of zero.



Details:





Comments:

I have an 02 Dodge Ram with the Cummins engine. Dodge recently

replaced the lift pum with an in-tank solution. I just had an led low fuel

pressue alert installed. Can you tell me what the minimum psi should be

fore WOT ? I noticed that if I go up a steep hill (and Ill bet if I pul

my 4000lb trailer) the led will light up.



thanks

 

[ThrottleJockey]

Oh yeah, it's right.



The VP-44 doesn't NEED a lift pump, it has it's own. But the problem is the lift pump in the Dodge application will fail and become a restriction in the fuel supply. No fuel to the VP-44 injection pump results in only bad things, as it uses the fuel for cooling AND lubrication.



Rig up a bypass when relocating your new lift pump to the frame rail.

 

[Gary - K7GLD]

Oh yeah, it's right.



The VP-44 doesn't NEED a lift pump, it has it's own. But the problem is the lift pump in the Dodge application will fail and become a restriction in the fuel supply. No fuel to the VP-44 injection pump results in only bad things, as it uses the fuel for cooling AND lubrication.



Rig up a bypass when relocating your new lift pump to the frame rail.

The "bypass" TJ mentions, looks like this as installed on a Carter 4600 pusher pump:



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It's function is to allow fuel to flow AROUND the pusher in case it fails - a full photo thread is available HERE:



http://turbodieselregister.com/forums/showthread.php?t=59880

 

[ThrottleJockey]

Yeah, that's it.



Gary's got a pretty neat truck.

 

[SAndreasen]

as preasure goes up your flow goes down simple hydraulics so it may be possible to have zero psi and fllow im glad to see somebody actualy has a spec from cummins

 

[BAnderso]

Gary ...

I am new to this so this may be a stupid question ... but wouldn't the bypass allow the pressure (when the fuel pump is working) to bleed around the pump?? Is there a check valve in the buypass??

Barry K3SUI

 

[Gary - K7GLD]

Gary ...



I am new to this so this may be a stupid question ... but wouldn't the bypass allow the pressure (when the fuel pump is working) to bleed around the pump?? Is there a check valve in the buypass??



Barry K3SUI

AH - you didn't go to the thread I supplied the pointer to up above, did you! SHAME! :-laf :-laf



Here, I'll save you the trouble - here's a couple of photos from that thread:



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What you are looking at is a homebrew "flopper valve" that is pressure operated - seals closed when normal operating PSI is present - opens when it's not, to allow nearly full flow AROUND the pump in case of failure - all entirely automatic!



SEE, the reason I provided that pointer, was to avoid posting those pics again!

 

[wlowe]

I copied Gary's setup but used a Carter bypass instead of making my own.

 

[Gary - K7GLD]

I copied Gary's setup but used a Carter bypass instead of making my own.

Wonder if you've checked the PSI that results from shutting down the pusher? Curious as to the efficiency of the commercial Carter valve vs my homebrew one. At idle, mine will lose 1 PSI as compared to available PSI prior to the pusher install - dunno what it woud be under a heavy load.



Nice install, by the way - and glad some of the junk I post here gets attention!. :-laf :-laf

 

[SAndreasen]

where do you by the bypass valve kit

 

[SAndreasen]

would like a parts list of fittings needed to make the bypass vavle

 

[BAnderso]

Very clever!! What about the stock lift pump failing in the closed position?? These are vane pumps and if failed with the vane obstructing the flow could starve the injector pump. Would one of these around that pump (without the fuel leak) allow rear pump to feed the VP44 or is this unnecessary because the pressure from the rear pump would force the failed front pump open?

Barry

 

[wlowe]

Originally Posted by Gary - K7GLD

Wonder if you've checked the PSI that results from shutting down the pusher?

As a matter of fact I did check that. When I pulled the pusher pump fuse the pressure dropped about 1 psi below the original OEM pump pressure so the check valve offers very little resistance. So far I am very happy with this setup, thanks for your very informative posts Gary.

Originally Posted by SAndreasen

where do you by the bypass valve kit.

Summit Racing, part number CRT-169-1002.



http://store.summitracing.com/partdetail.asp?autofilter=1&part=CRT-169-1002&N=0&autoview=sku

Originally Posted by BAnderso

What about the stock lift pump failing in the closed position??

I've considered this problem also but haven't verified it on my truck. Research on the TDR was inconclusive as some members reported that it blocked flow and some said it did not. I personally see no problem in using a by-pass valve around the OEM pump to guarantee flow if the pump fails.

 

[Gary - K7GLD]

Very clever!! What about the stock lift pump failing in the closed position?? These are vane pumps and if failed with the vane obstructing the flow could starve the injector pump. Would one of these around that pump (without the fuel leak) allow rear pump to feed the VP44 or is this unnecessary because the pressure from the rear pump would force the failed front pump open?



Barry

GOOD point - as as a matter of fact, my stock LP *did* stop on me in very bad situation, the engine stumbled, and I saw my PSI was ZERO!



The LP had managed to stop in it's rotation at a point that nearly tottaly blocked flow of fuel, even thought the pusher was still functioning perfectly. I was able to continue at about 40 MPH - on a crowded freeway - for about 25 miles to our destination, just barely maintaining positive fuel pressure.



Turned out, the power plug to the LP had come loose, and the pump stopped - all I needed to do was reseat the plug, and all was well.



I knew better, procrastinated, and paid for it - and now BOTH pumps in my system have protecting bypasses! :-laf :-laf

 

[BAnderso]

Thanks for all the good information!! I now know what I have to do with my fuel system. I really like this truck. The engine runs fantastic ... but I was concerned about sending a Grand off to Dodge on a regular basis because of problems with the fuel system. I'll have to get this setup ... and then start learning a bit about the steering linkage and it's problems ...

Barry