Engine/Transmission (1998.5 - 2002) GPH on stock lift pump?

[justinp20012500]

Does anyone know how many gallons per hour the stock carter lift pump is supposed to provide?

 

[FourBarR]

e-mailed cummins long time ago for this info, never got an answer. so much for customer service.

 

[Ncostello]

If memory serves me correctly... . I believe it was 45 GPH.

 

[jtisdale]

I was thinking it was like 90gph. I thought I read somewhere the factory pump will circulate a full tank every 20 minutes. But, I may be off my rocker.

 

[15w40]

Several years ago I measured the output flow of the stock Carter lift pump. The graph below shows gallons per hour on the X-axis verses pressure on the Y-axis. The way to read this is, at zero pressure, or with the pump free flowing into a pail there is a flow of 85 gallons per hour. If the pump is deadheaded or blocked off, the flow is zero and pressure is 16 psi.

 

[Ncostello]

I can hardly see the graph... but from the looks of it between 10-12psi would produce results around 40-50 GPH... or so. The good ole pump curve.



Not saying there is anything wrong with the graph as is... but personally I would have put psi on the X-axis since thats something you control... and GPH on the Y-axis is the result of that "function" in a round about way. Of course the graph would still appear the same in form. Maybe your graph is what I remember 15W40

 

[MCummings]

justa bump



Merrick

 

[15w40]

OK, you guys have shamed me into plotting the Carter flow again. The test was run a couple of years ago using a new lift pump. I remember that day well as I got soaked with diesel when the hose running into my catch pail took off like a rocket. The hose waved around soaking my workbench and me as I tried to capture it.

#ad

 

[pcarlson]

15W40,



Without re-reading the 157 posts to your test in 01 with Bill K, what was the final verdict of the stock pump, volume verses psi. If I remember right the stock pump was more than enough for our applications?



The high volume carter is 110gph and the factory one I thought was rated in the 80-100 gph range.

 

[15w40]

Pcarlson, the stock Carter pump has enough flow for a stock engine with a 5-psi drop across the partially clogged fuel filter. The flow measurements I made by supplying 12 volts to the pump. It will flow more at a higher voltage. My truck typically was supplying 14 volts to the lift pump when it was in stock form. At 14 volts the flow would easily be above 100 GPH.



I wish I knew how to post a good looking drawing. JPEG just doesn't look good.

 

[Gary - K7GLD]

The graph looks fine, and the info is great - thanks!

 

[pcarlson]

15W40



Thanks for the info. Your graph's were just fine. So based on your reasearch what kind of fueling would I require based on my signature? Pressures seem fine they draw down to about 8psi @WOT and 14-16psi at idle.

 

[15w40]

I think you will get many opinions on how much pressure is enough to keep the VP44 happy. We have all heard of some applications of the VP where no lift pump is used. There have been a couple of reports here on the TDR forums where engineers from Bosch, the maker of the VP, claim that pressure as low as -2 psi is OK, and another engineer has reported as low as +2 psi is as low as you can go.



I recently got a copy of a CD published by Bosch, “Radial Plunger Distributor Pump VP44”, where the function of the VP44 is explained and diagrammed. One section I found related to the fuel needed by the VP44 was the section on delivery of fuel to the high-pressure portion of the injection pump. The internal supply vane pump accomplishes this. It states that fuel entering the VP is drawn into this vane pump from the fuel tank. (They don’t mention the need for a lift pump. ) The supply vane pump is driven by the drive shaft that is driven by the engine and supplies a constant amount of fuel per revolution to the interior of the VP. It goes on to say the supply pump delivers a speed proportional pressure to the interior of the VP. At some high pump speeds a valve is used to limit the pressure in the interior of the VP by opening a spring-loaded valve that dumps pressurized fuel back to the inlet port. This is the same port that the lift pump is connected to and causes all the spikes in pressure that kill the fuel pressure senders. In my opinion, it also kills the lift pump by constantly working its spillback valve as the fuel flow to the VP stops and reverses. Inside the VP there is mention of a diaphragm that acts like an accumulator to store pressurized fuel in the pump interior. It is this fuel that is used by the high-pressure radial pump for injection and also gets spilled back to the input port. There is no mention of what pressure the interior of the VP can reach but I assume it is higher than any lift pump used. I base this on the size of the internal supply pump.



So to sum up on what pressure is needed, my opinion remains that any positive pressure is enough. The one exception I can think of is if the Cummins ISB is making huge horsepower using a box and showerheads. In this case the flood needed to the VP input port might be more than the small inlet port dimension can flow without a high lift pump pressure.



I wish someone would publish data on the VP44 fuel flow needs vs. horsepower. With these data it would be easy to design a low-pressure fuel system between the tank and injection pump and we all could stop guessing.



If anyone is looking for info on the VP44 try this Bosch web site:



http://www.boschservice.com/http-docs/access/traincd.html

 

[Ncostello]

Thanks for that link 15W40. So is that CD worth having? I love to read about and know what makes things tick... especially the things I use.



The accumulator topic on the VP is interesting. The ISC8. 3 injection pump is called the CAPS pump... short for Cummins Accumulator Pump System. It uses a Carter transfer pump almost identical to the one on the ISB except it has a bigger mounting bracket that also serves as a fuel line junction point. However... this pump only runs for 30 seconds on startup then shuts off. The injection pump takes care of itself after that. I think the mounting bracket/head has some internal flapper valves or something because there are multiple fuel line connections there. Must be some kind of bypass deal for when the transfer pump kicks off.



If any kind of measureable pressure at the VP inlet exists... it must point to the fact that some resistance to flow is present inside the VP and therefore all the fuel that is required is being delivered with some excess. If 0 psi is measured... then maximum flow of the lift pump would have been achieved. This would assume of course the lift pump is function normally and isn't really broken... since a junk lift pump would also show 0 psi except without the corresponding flow of fuel.



Here's the big catch which messes with our thinking. A good lift pump provides 15psi at idle and 10 psi at WOT when new. These are just estimates for example. So we drive around with these numbers in our head all the time. Then when we all of a sudden start seeing 2 psi at WOT we get worried. So why is 2 psi in this case bad?



Well... I think 2psi may be sufficient but there is a problem. What was once providing 10psi is now doing 2psi... so that lift pump is obviously malfunctioning somehow. Its not what we expect it to do. Folks assume if 10psi is what it got originally under WOT... then it always needs 10 psi. Its hard to accept that something is performing terribly yet still sufficient. However... you cannot ignore the fact the lift pump has gone bad and it will only get worse and eventually totally fail perhaps.



You made some very interesting points.

 

[justinp20012500]

All you guys are great help. Very good information.

 

[15w40]

Ncostello, I think the Bosch CD about the VP44 is OK but doesn’t get into enough detail. Having said that, I did learn a few things about how the VP works. The CD has animation of the pump timing and the high-pressure radial pump.



I see this CD as an introduction to the VP but it fails to get into the fine details. I was hoping to find out about fuel rates, pressures, the radial pump volume, and some of the fuel pump control module details. None of this was presented.



Maybe I should enroll in a Bosch course about rebuilding the VP44.



justinp20012500, glad to help. I think we all learn by these questions.

 

[justinp20012500]

15w40



If you enroll in a advanced VP 44 class and find out the inner workings of that thing, I will be the first one in line to get one of your super hotrod VP pumps!!!

 

[JPLB22]

15w40



I was playing some phone tag with Bosch, trying to speak with someone with some real expertise on the the VP44. At one point they suggested I purchase the CD your talkin' about.



The reason I wanted to talk with an " authority ", was because I also was concerned about the minimum inlet pressure for healthy VP44 life. I was not successfull in my quest to speak with an " authority ", nor did I purchase the CD .



I did start a thread a while ago on the minimum inlet pressure for healthy life of the VP44 though... . the feeling that I got from the thread was that 2 psi would be more than addequate to run a CTD, but not enough to run a CTD and cool the VP44.



I thought the same thing, that if there is a positive pressure at the inlet to the VP44, then all would be well, caue the VP44 would not have to do any work to pull it's own fuel. I think it would be very informative to have a flow meter and a temp gauge on the return line from the VP44 to the tank. I don't know much about flow meters and how they work, but a temp gauge shouldn't be too hard, should it ?????



I think having as much discussion about these VP44's as possible is very beneficial to everyone who owns and 2nd Gen 24v.



Jeff

 

[15w40]

JPLB22, I remember that thread. Many people have said that a high lift pump pressure is needed to cool and lube the VP but I was not won over by that thought. After viewing the Bosch CD, I am now convinced that any positive pressure is enough. This is because it states that the internal supply pump will displace a “CONSTANT VOLUME OF FUEL PER REVOLUTION”. I see this as stating that the pump displacement times the RPM will determine how much fuel passes through the VP and is independent of lift pump pressure. Because the internal supply pump is a positive displacement pump, the cooling and lube does not increase with increased lift pump pressure. The only time I would worry about cooling the VP is if a clogged fuel filter created a negative fuel pressure or a bad Carter lift pump blocked flow.



I am not trying to say that I am 100% correct and there may be some modified engines that benefit from a higher lift pump pressure. I just don’t see that 99% of us should be concerned with low pressure. Ncostello does bring up a good point about low pressure being one of the signs that a Carter lift pump is dieing and I agree that there should be a gauge or alarm to tell you when the pressure is low.



Also it appears that running a higher, than stock, pressure to the VP is not a problem except when starting. If the aftermarket pump is more reliable than the Carter, “It’s a good thing” (quoting M. Stewart).

 

[Ncostello]

There exists a thread already where MoparMuscle did in fact put a flow meter on the return line. Among other things it was tested under different circumstances... such as stock, bigger banjos, bigger lines etc. There seemed to be a limit to what would be returned to the tank.



I dont exactly remember... but I thought it was in the 30's GPH for return. Seems that the VP would return a fairly constant amount no matter the inlet pressure under WOT conditions.