2nd Gen Non-Engine/Transmission fuel flow

[RobertMiller1]

If you install a bed aux fuel tank, which is much higher than stock fuel tank, and is much closer, would you need a Lift pump at all before the VP44?



I would think not since there are several installations of this cummins engine and pump where a lift pump is not used.



A rear mounted transfer pump from main to aux pump would of course be required, but it would not need to be running as often and as long.

 

[15w40]

Many of the Cummins 6B engine applications do not use a lift pump and use only gravity to feed the injection pump. These applications are things like stationary generators or air compressors.



In a Dodge truck it is risky not to have a lift pump to provide pressure in a dynamic situation. When accelerating, a bed-mounted tank will not provide any pressure to the engine. If it is only 1 foot higher than the engine, it will only supply about 1/3 psi of fuel pressure when the truck is not moving. What happens when the filter starts to clog?



Stick with a lift pump.

 

[Gary - K7GLD]

NO lift pump is NOT better than a poorly placed one...

 

[RobertMiller1]

dunno,

I have a turbo diesel Isuzu Trooper. The Robert Bosch pump has plenty of pumping capability. There is no lift pump on the Trooper. Suspect there have been a lot of diesels over the years that only use the injection PUMP without a Lift Pump. Now if you BOMB that is an entirely different animal.



I think the VP44 pump is underestimated.

It apprears the lift pump may have caused more problems than it is worth.



There is a letter here on the board somewhere from the Cummins rep addressing that issue.



I'm not at this point advocating eliminating the lift pump, just exploring ideas on how this weak point can be eliminated with a fuel delivery design change.

 

[Gary - K7GLD]

"I'm not at this point advocating eliminating the lift pump, just exploring ideas on how this weak point can be eliminated with a fuel delivery design change. "



YEAH, maybe, IF you could raise the fuel supply about 50 feet in the air...



OTHERWISE, you will get precious LITTLE head PSI from gravity alone, REGARDLESS of supply line size or fancy fittings - PSI in a gravity system is determined PURELY by vertical drop - and at LOW drop, the least obsticle, plugged filter, etc, WILL shut you down!



And I suspect the built-in mechanical LP inside the VP-44 provides an even POORER fuel mover than the Carter does... Anyone ever check out the relative RPM and swept volume of the vane pump in the VP-44? I know it's operating RPM is determined purely by engine/VP-44 RPM, but wonder what it's flow rate is at nominal cruise speeds - I suspect it is considerably LESS than the constant speed of the outboard Carter LP...

 

[Ncostello]

Suspect there have been a lot of diesels over the years that only use the injection PUMP without a Lift Pump

I dont know how many but yes its true. One fire truck we have sucks fuel from the tank through 22 feet of 1/2" line and two filters without the use of a transfer or fuel pump. And the tank is lower by some degree.



But its injection pump is designed to do that I would suppose whereas the ISB VP44 isn't. Each pump is different of course. B-Series in automotive applications usually have pumps designed into the delivery system for good reason.



The internal lift pump to the VP44 probably isn't any kind of transfer pump at all... except to get fuel moving inside the VP itself.

 

[RobertMiller1]

The VP44 is a fuel pump. And quite a good one.



Your suggestion that gravity would be all there is. That simply is not the case.



The lift pump is the weak link.

 

[Ncostello]

Some injector pumps have powerful rotary gear type (and other types) inlet pumps that will pull fuel on their own nicely. They dont need help with a transfer pump or gravity. I dont think the VP44 is like that. Some need help.



I'm saying the VP44 is an electromechanical high pressure injector pump... and the transfer pump is a low pressure fuel pump. The transfer pump can be argued to be a weak link. Removing this weak link means there is no link at all. Fatal error with a VP44 in my opinion.



Monitor the weak link or make it stronger. Or you can remove your transfer pump and run without one. Let us know the results.

 

[RobertMiller1]

"... Removing this weak link means there is no link at all... .



I'm saying this is wrong



The VP44 is a strong pulling pump.

 

[Ncostello]

I suppose I didn't know the VP44 was a strong fuel puller on its own. Where did you find this info. . or how do you know that? Just curious.



If I understand you correctly... you are saying the lift pump is a weak link and can possibly be removed to better the system. You also are saying the VP is a strong pulling pump and can do without the lift pump.



Then you state removing the lift pump is wrong. I'm not trying to be smart but rather making sure I understand you correctly.



I too have tossed around the idea of losing the transfer pump and just relying on the VP44 alone.

 

[RobertMiller1]

do a search for the article from the cummins representive on this board.



I'm like you, just looking into alternatives. So far, moving the lift pump to the rear with a bypass valve ( where the vp44 can still pull) seems to be best alternative.



If I find the afore mentioned post, I will reference it here.

 

[Gary - K7GLD]

The structural design of the VP-44 LP *LOOKS* exactly the same as the pump portion of the Carters - unknown is the speed it is turning in reference to engine speed, and actual volume capabilities as compared to the stock Carter...



Without more documented info, I tend to doubt that the VP-44 LP would function any better than a properly functioning Carter in terms of power, PSI or volume capabilities - we DO know from previous testing, that maximum flow thru the entire VP-44 maxes out somewhere around 45 GPH at maximum load...



BUT, I'm willing to be educated - so educate me!

 

[15w40]

I believe the Bosch engineers said that the VP44 was happy with a fuel pressure (vacuum) as low as -2 PSI. The reason Cummins and/or DC use the external lift pump is to allow priming after changing a fuel filter and also to provide adequate pressure as the fuel filter clogs.



One other point to consider is with low fuel pressure, a sudden increase in demand from the VP44 will create a negative fuel pressure. This can happen with a sudden increase in engine speed. Fuel in the fuel line will have to accelerate to get up to the demand flow of the VP. In cold weather, when the fuel is viscous, it may take some time to flow through the 10-micron fuel filter. This is where a higher pressure will help. A fuel pressure gauge on a stock engine will show a dip of several PSI when revving the engine in warm weather.

 

[rweis]

here is a different . 02



bed tank and PRESSURIZE it to 20psi and keep it pressurized



relieve the pressure, fill it, repressurize it



VP still gets fed



You then set the pressure to whatever psi you want



just an idea



Bob Weis



outside the box?



my OEM lp has 27k, RACOR 690 prefilter, regulated to 12psi with Mallory 4307M, AN-6 lines, Aeroquip fittings runs like a top (which means probably tommorrow it will crap out)

 

[Ncostello]

I've read that article a couple times way back when. I dont remember everything it said but I dont think there was anything in it that really helped me much in my dealings with lift pumps and such. Good info but it didn't have what I was looking for.



Rweis... I like your thinking but may have a point. When I couldn't get my lift pump (stock location) to suck fuel after a filter change... I tried regulated air pressure to maybe push some fuel and get the air lock out. It didn't do a thing. I figured it was because the air pressure also goes into the return line and puts an equal pressure on that side. Thus the supply side was pushing against the return side in equal amounts and nothing moved in the system.



I havent tried all the fixes and will not comment on which is best... but moving the pump turned out to be everything I had hoped it would. I cannot complain about the performance of my lift pump back there by the tank which is where I felt Cummins should have put it to begin with.