Engine/Transmission (1998.5 - 2002) Stupid lift pump question

[daveshoe]

I was really impressed with the posts on 'Wanna fix your lift pump problems'' The two schools of thought are either move your factory pump to a low, rear position to make it push the fuel instead of sucking it; other thought is a separate pusher pump to feed the stock pump in its original location.

To keep this short I know that a low pressure [3-5] PSI pusher would be fine to feed the stock pump. The question concerns VOLUME I found a pusher that I think is 'dead reliable'' but it only puts out 12 gallons an hour. Am I correct in assuming that an output of this volume would actually cause a drag or suction instead of a low pressure boost to the stock pump?

I am posting this on the first time forum because the responses on this forum seem to focus on helping us learn instead of berating us for what we do not know. All that does is change to

 

[Whitmore]

Dave, you are correct, when a seried pump system is in place they have to work together IE one pumps suction is the other pumps discharge and with the numbers you report I can tell you from much pumping experience that with the first pump only doing 12 gph and the second pump TRYING to do 70 gph that your second pump will be working very hard and actually pulling fuel thru the first pump... ... ... ... ... ..... if that makes sense, I would highly recommend a fuel pressure gauge at the discharge of both pumps if you opt for the seried pumping setup, this way you can actually monitor pressure at both pumps. But keep in mind that this may give you some false indication of what is actually going on here because you second pump being the higher flow pump could have all the load as the first pump simply coasts thru .

Why are we looking at pressure instead of volumn, this is a great question and the answer is simple... ... ... ... ... ..... Pressure is easy to measure and is also cheap, volumn is expensive to measure, Keep in mind that if pressure drops so does the volumn in this case, lets look at a garden hose for a minute though, if you have no nozle on the end of a hose and just turn it on and let it free flow you can get say 20 gallons a minute at maybe 40 psi, now you put a nozzle on the end of the hose and restrict it down to a small hole so you can squirt 30 feet, now the conditions have changed, you now have say 5 gallons a minute but the pressure has climbed to 70 psi.



What is important to us is flow, we need enough flow to supply the injectore as well as excess flow to go thru the vp-44 for cooling and lubricity, keep in mind with our fuel system that if we show no psi or low psi that the flow rate has decreased signifinatly.



I did the ultimate test with my system since I had a golden chance, My return line is very convenient since I use my in-bed auxillary as my main feed, I took a clear piece of hose and made a loop up above the inbed tank so I could watch it flow as I drove, it is very hard to see how much flow was happening but I can tell you that at WOT the flow in the looked to be the same as when just cruzing, this tells me that my delivery system is adequate for my needs my psi is 15 at cruze and 12 at WOT, and I do this with 1 pump. I prefer to stay away from seried pumping when a single pump installed in a proper way can do the job just fine.



cheers, Kevin

 

[aharrow]

so how much flow is actually needed for the VP44 in gph or gpm does anyone know can someone from the pump manufacturer tell us how much is needed to supply,lube, and cool the pump so if I am right flow is more important than pressure help me if I am wrong.

 

[Ncostello]

Whitmore, what do you mean you don't run a lift pump and don't want one? Or are you refering to your single pump as a "transfer pump" since it doesn't do any "lifting"?



15W40 posted the Carter OEM will put out 90 GPH @ freeflow... 60 @ 8psi and 25 @ 14psi. Which makes sense with your garden hose example Kevin. Except in your statement you further describe when we see 0psi or low psi you say our flow is decreased significantly.



But 15W40's numbers say that at idle pressure (14psi), we flow 25GPH and when its full throttle we may see 60GPH. So it would stand to reason that as our pressure gauges go down, our flow goes up as the pump is able to get closer to free flow conditions. Pressure goes down because the VP44 becomes less of a restriction as it pumps more fuel out the other side to the injectors.



If my thinking is correct (and I could be wrong) maybe its not a terrible thing when a pressure gauge goes all the way down to 8psi... . thats assuming you have a good pump. Of course a bad pump will go down to 8psi but not be anywhere near 60GPH.



Just thinking out loud on this.

 

[Whitmore]

Originally posted by Ncostello

Whitmore, what do you mean you don't run a lift pump and don't want one? Or are you refering to your single pump as a "transfer pump" since it doesn't do any "lifting"?



15W40 posted the Carter OEM will put out 90 GPH @ freeflow... 60 @ 8psi and 25 @ 14psi. Which makes sense with your garden hose example Kevin. Except in your statement you further describe when we see 0psi or low psi you say our flow is decreased significantly.



But 15W40's numbers say that at idle pressure (14psi), we flow 25GPH and when its full throttle we may see 60GPH. So it would stand to reason that as our pressure gauges go down, our flow goes up as the pump is able to get closer to free flow conditions. Pressure goes down because the VP44 becomes less of a restriction as it pumps more fuel out the other side to the injectors.



If my thinking is correct (and I could be wrong) maybe its not a terrible thing when a pressure gauge goes all the way down to 8psi... . thats assuming you have a good pump. Of course a bad pump will go down to 8psi but not be anywhere near 60GPH.



Just thinking out loud on this.

Neil,



when I say I dont have a lift pump that is exactly what I mean, I took mu oem lift pump and moved it back on the frame under my in-bed fueltank where fuel with head pressure of 1 pound is being supplied to the suction side of my pump... ... ... ... ... ... ... ... ... ... ... ... my pump no longer lifts fuel at all and is now considered a delivery pump!



15-40 is absoluty correct with his numbers, he has done extensive research on this issue and although doesnt post alot is one of the most knowledgable members we have on this board, I commend him for his commitment on our desire to resolve the fuel delivery issues, he and I have done much PM ing in the past . OK now keep in mind that the VP-44 has an internal pump too, what we are concerened with is fuel delivery TO the vp-44 from your lift pump or my delivery pump, if the pressure goes to 0 psi than that means the flow has stopped OR that also means that the injectors and the vp's internal pump are using ALL the fuel that the Lift or delivery pump can supply, in this case it simply meand you need to up grade the system because the internal pump is doing most of the work .



cheers, Kevin

 

[Ncostello]

Kevin, I just thought your sig saying you "dont have or want a lift pump" was neat... . I like that. Kinda makes a strong statement on the issue of how to solve the problem. Just so you will know, I agree with you completely on this issue. I just like pointing out some things worth noting.



I know 15-40 is very knowledgeable... I've read most of what he has posted in the past on this topic... and agree his research is invaluable.



I was just thinking that *if* a transfer pump system was properly working and everything was in tune... . a low pressure situation would simply mean the VP is pulling alot from the transfer pumps supply side... which means the fuel is really flowing in terms of GPH. And good flow volume is an important consideration in longevity. Guess what I'm saying is that low psi coupled with great volume is really not a problem. Whereas low psi coupled with poor volume is a major problem.



I really wouldn't be afraid if my gauge read 5 psi and I knew for sure that I was getting a great volume of flow to the VP. But thats hard to do like you said. Low pressure does not always mean that there is inadequate flow. Of course I doubt the OEM filter would support 60-70 GPH of low pressure flow.

 

[Whitmore]

Neil, I have psi readings before the filter and after the filter and it doesnt matter what kind of a reading I get at the VP-44 the DP across the filter is always a pound or less, this tells me that at my HP level the filter is adequate for my application



cheers, Kevin

 

[Gary - K7GLD]

HMMmm - for the sake of discussion, how many column inches of diesel fuel does it take to equal 1 psi? And Kevin, does your 1 psi estimate refer to a FULL tank - or down near empty?



*I* have a positive pressure to my pusher as well, down to about 1/2 tank... But not enough to get particularly excited about...

 

[Whitmore]

27" of water column is equal to 1 psi, water is heavier that diesel so I dont know about it, the reading of 1 psi is when I have a full tank of fuel, I can tell when my fuel level is getting empty because I go from 15 to 14 at 75 mph and at WOT it will go down to 12



cheers, Kevin

 

[Gary - K7GLD]

UMMmmm - diesel is HEAVIER than water - you're saying water will FLOAT on top of diesel?



I don't THINK so!

 

[daveshoe]

Get the numbers

One thing I plan to do is record readings from the lift pump right before I move the pump to the rear. One probably should try to run the tests with the same weather and wind conditions and with truck to full operating temp. ect. Mine presently makes 12. 5 at 70 MPH. If moving the pump helps , I would expect to see the most pressure differential in a stock motor at this level and above

Thanks for the great explanation ,Kevin, I know it takes some time and patience to do this.

BTW I wonder why at the death of some of the lift pumps ,the truck ceases to run and some trucks go on until the next filter change. I recently changed a gasser chev fuel pump [vane] and sucked and then blew on it . It was evident that it had a check valve. I slowly moved the vanes by hand and could not create a condition that caused much of a vacuum resistance at all

Our pumps may be different than this, but I wonder if a failed check valve or a very small fuel line ''leak'' may cause the first condition. I am especially interested in Gary's thoughts on this because of his pusher installation.

 

[Whitmore]

Dave, my original lift pump failed because the spillback ball and spring affair was weak and was opening to spillback conditions when the pressure got to 4 psi, this caused the fuel to constantly be spilling back to the suction side of the pump whenever the psi got to 4, this happened when the truck had 23k on it, that is way early, I did a complete teardown and diagnosis on it and the drive motor looked fine and the coupling also looked good too.



cheers, Kevin

 

[terrywerm]

Interesting twist on column inches of fuel to get 1 PSIG

Just for those who are curious and wanted to see some accurate numbers:



Water: 8. 333 Lbs/Gal, 27. 721 column inches = 1 PSIG

Diesel: 7. 462 Lbs/Gal, 30. 956 column inches = 1 PSIG





If a stock underbed tank was 10 inches tall ( I didn't go out and measure, it's cold and dark out ), full of fuel, (putting the fuel depth at 9 inches due to expansion space) and the pump inlet was 1 inch below the bottom of the tank, the total head would be 10 inches and there would be 0. 323 PSIG at the inlet of the pump - when the system is static (pump not running).



With a large in-box auxilliary tank 24 inches tall and full of fuel (fuel level would be at 21. 6 inches due to the federally mandated 10% expansion space), and the pump inlet was on the frame and 10 inches below the bottom of the auxilliary tank, the total head would be 31. 6 inches and you would have 1. 02 PSIG at the pump inlet - also when the system is static (pump not running).



So, with a full in-bed auxilliary tank, Kevin COULD show a reading of 1 PSIG at the pump inlet - but he wouldn't get that off of the stock fuel tank. No matter what tank is used, the inlet pressure would drop proportionally as the fuel level in the tank went down.

 

[Whitmore]

Thanks for that info Terry, I was kinda flying from the seat of my pants on the figures so this confirms my original thoughts.



cheers, Kevin

 

[Gary - K7GLD]

My comment concerning Kevin's post was on the part about diesel being heavier than water - not true, as described above... Easy to place a small amount of diesel and water in a container, and see which liquid floats - and it's pretty clear that the water drains on our fuel filters are on the BOTTOM of the container - not the top...



AND, not to open a whole NEW bucket of worms, but ANY actual fuel pressure measurement in the SYSTEM, is only relevant relative to the REST of that system - NOT to the outside atmosphere - it's NOT as though there was 1psi on on ONE side of the pump, and less on the other - until the pump is actually activated! The only issue of actual importance as far as any real advantage is concerned, is the DIFFERENCE in fuel level at each END of the line - what happens at various points in between are largely irrelevent in terms of pressure!



To illustrate, that 1 psi mentioned, is ONLY if the flow is open to the outside of the hoses/fittings and flowing freely - otherwise, it merely equalizes along the length of the fuel path - in other words, you might see 1 psi at the inlet to the LP in relation to the outside atmosphere - but you would ALSO see it ANYWHERE else along the fuel path at that same level - NOT just at the inlet to the pump - and that pressure in relation to the atmosphere will steadily DECREASE as the fuel path rises back up to engine level - the IMPORTANT element in all this is where the fuel level source is in relation to the ENGINE - not necessarily where it is in relation to the LP itself - though having the LP closer to the fuel source and lower than the fuel level is an obvious advantage in our case...



More grade school physics - and undoubtedly food for more debate...

 

[Whitmore]

Originally posted by Gary - KJ6Q





AND, not to open a whole NEW bucket of worms, but ANY actual fuel pressure measurement in the SYSTEM, is only relevant relative to the REST of that system - NOT to the outside atmosphere - it's NOT as though there was 1psi on on ONE side of the pump, and less on the other - until the pump is actually activated!



To illustrate, that 1 psi mentioned, is ONLY if the flow is open to the outside of the hoses/fittings and flowing freely



More grade school physics - and undoubtedly food for more debate...

Gary , please explain the following measurments to me



Flow pressure



Static pressure



Residule pressure

 

[Gary - K7GLD]

"Gary , please explain the following measurments to me



Flow pressure



Static pressure



Residule pressure"



Sure Kevin - it's clear a few here are deeply confused on the above...



Keep in mind ALL these are INTERNAL system pressures, NOT the irrelevant differences between those, and EXTERNAL pressures that might have no contributing or consequential effects. but against which pressures are compared!



FLOW PRESSURE is that pressure of a fluid or gas that may be present between 2 points as it moves WITHIN the confines of its enclosure, and as taken at specific points in its travel - such as the pressure between your LP and the fuel filter. It can and usually does change at various points in it travel due to restrictions or similar influences.



STATIC pressure is the pressure of a fluid at REST, and free of internal or external influences - that would be the pressure inside your fuel system as it is at rest, nothing operating - that might be the 1 psi you would measure at the inlet to your pump, or anywhere along your fuel system, relative to the source/destination - it does NOT mean you have a built-in 1 psi "forcing" fuel flow beyond the pump, since in STATIC condition, that SAME 1 psi is also present on the OUTLET side of your pump!.



RISIDUAL PRESSURE is similar to static pressure, OR the pressure that remains AFTER internal or external influences that might change it have been removed - or the pressure inside a tire after inflation... Risidual and latent mean much the same thing - that which remains, or is left...





Take a length of hose. let it droop roughly 60 inches in the center. and fill it with water. then leaving BOTH ends open - static pressure at the the LOWEST point in that hose as measured against ambient EXTERNAL atmospheric, will be roughly 2 psi - but will that 2 psi at THAT point push ANY liquid ot either end?



NO, because it all equalizes internally! Lower ONE end of that hose, and you now have both flow AND pressure GREATER at that end because it is now LOWER and at greater pressure than the rest of the hose and its contents - and as long as the hose is held at a steady height at BOTH ends in relation to the middle, both static AND risidual pressure are present in the middle and various points in between - and those pressures will vary at different points, depending upon their relative heights...



You don't necessarily have 1 psi head pressure at the inlet to your pump in FLOW pressure - you only have the psi DIFFERENCE between the height of your fuel at any given time, and the far end of the fuel system and ITS relative height... The height of the line in BETWEEN is largely irrelevant as far as functional system psi is concerned, and while PRESSURE is present and measurable, there is no FLOW!



Do you think that if you could somehow drop your pump several MORE feet, leaving all else the same, you would GAIN even more "head pressure"? NOT gonna happen, because every foot you GAIN on the DOWNHILL side, you must then overcome on the UPHILL side, and one cancels out the other!



Don't misunderstand me Kevin, your setup is a good move upscale from what most of us have done by remaining with the stock tank and location - and once you start actually pumping fuel in your setup, the additional height of your fuel source comes into play at least to a degree.



Only question is, how much real-world improvement will it provide in comparison to what most of us are using? Your added tank is undoubtedly different than mine - mine is a 50 gallon, and maxixmum height of fuel above the bed is only about 11 inches, and wouldn't gain me much in maximum fuel pressure at the fuel filter on the engine - perhaps 1/3 lb psi on a completely full tank - really not enough to get lathered up about...

 

[Whitmore]

AH, now its clear to me, can I get my grade school physics diploma now?



I sure wish I would have known all this grade scool stuff when I taught hydrolics in the Fireservice for 15 years.

 

[Gary - K7GLD]

AH well, O learned one - feel free to correct my many glaring errors...



I'm always willing to learn - and something mighta changed since I was in the seventh grade...



You know - like diesel fuel getting heavier than water, and such...

 

[terrywerm]

Who said diesel fuel is heavier than water?

I've gone back through this entire thread and I cannot find any place where anyone said that diesel fuel is heavier than water. The first reference to the difference in weight between the two was this one by Kevin:

27" of water column is equal to 1 psi, water is heavier that diesel so I dont know about it, the reading of 1 psi is when I have a full tank of fuel, I can tell when my fuel level is getting empty because I go from 15 to 14 at 75 mph and at WOT it will go down to 12

It appears to me that this says "water is heavier that diesel". I assume the word 'that' was meant to be 'than', and is a simple typographic error.



The next reference was this one:

Water: 8. 333 Lbs/Gal, 27. 721 column inches = 1 PSIG

Diesel: 7. 462 Lbs/Gal, 30. 956 column inches = 1 PSIG

It appears to me that this one also says that water is heavier than diesel fuel. Of course the opposite would be true if modern mathmeticians have arbitrarily decided that 7 lbs. is heavier than 8 lbs.



Now I know that my eyesight is not getting any better as the years tick by, but I don't think my eyes have totally given up yet.



So now for the inevitable question: Who in blazes said that diesel fuel was heavier than water?