Engine/Transmission (1998.5 - 2002) supply pressure for VP44

[CWright]

I'm wondering how much supply pressure is to much for the VP44 injection pump? After 5 oem lift pumps last one in the tank I finally installed an Air Dog. The pressure now runs 22 to 23 lb. normal driving and drops back to 18 or 19 at WOT. I thought about 16 was max. But not really sure. Any information would be appreciated. Thanks Clayton

 

[FYarcho]

When I installed my walbro pump it was running around 22-25. I dont know if that is actually bad or not. But I was having a problem with starting if I stopped for a few minutes and tried to start again. After I go the pressure below 20 everything was fine.

 

[mhenon]

I'm wondering how much supply pressure is to much for the VP44 injection pump... .

This is from Blue Chip Diesel:

"We proved on a dynomometer in 1998 that if you have 5 PSI, under load, you can make all the power available from a VP44, and 5 psi will provide plenty of return fuel for pump lubrication. We do not recommend running more than 12-15 PSI as that does NOT help the fuel system in any way. In fact higher pressures could diminish fuel delivery to the rotor and make the truck run worse at high RPM and possibly overheat and damage the fuel bypass solenoid. "



Mike

 

[JSawtelle]

5 X $160. 00 per pump? = ?????? Probably an aftermarket remedy. I have been ultra happy with my FASS 150/150. I know there are other solutions out there. Just my . 02 cents worth. It runs at a constant 14 lbs.

 

[CWright]

No they were all under warranty.

 

[Mundgyver]

Open up your delivery line from the tank to the pump to the VP to 3/8 or 1/2 ID. Next step is to ditch the banjo polts and use straight in connections for the fittings. Set your delivery pressure to 15 psi. The overflow valve in the VP is set to open at 14 psi.



The increase in the diameter of the fuel line allows for a greater volume of flow for fuel. This allows the VP to take on what it needs without hydraulic locking due to over pressurizing, hense 15 psi delivery to the VP.



I have 200,000+ miles on my original VP with no signs of weakness, never had any hard starts and have all the power I can use. All the fuel runs through a Hayden automatic transmission cooler designed for a 16,000 GVW application. This cools the fuel before the VP to help keep the electronics from overheating.



I have been using this set up for several years with no problems.



Food for thought

 

[ed9824v]

I'm wondering how much supply pressure is to much for the VP44 injection pump? After 5 oem lift pumps last one in the tank I finally installed an Air Dog. The pressure now runs 22 to 23 lb. normal driving and drops back to 18 or 19 at WOT. I thought about 16 was max. But not really sure. Any information would be appreciated. Thanks Clayton

I to have the air dog with 24psi to 20psi range never less I have herd the same as you. I am taking the reading both manual and digital right off the AirDog pump housing not at the VP but don't expect much of a pressure drop with the 1/2in lines Ed

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[Mundgyver]

Something you should be aware of when looking at your delivery pressure from the LP is that inside the VP-44 there is a timing device that is hydraulically assisted. Too much delivery pressure and you can wind up changing the VP's ability to perform it's function. Thats why volumn of flow is more important than pressure. Too much pressure causes hydraulic lock problems and too little volume causes starvation. By increasing the delivery volumn while keeping the pressure optomized to the pumps ideal feed pressure will prevent starvation and will allow the pump to use as much fuel as it wants to without being forced to.



It is a balancing act.



This information is available in "The Bosch Yellow Jackets Edition 2003, Tistributor-Type Diesel Fuel-Injection Pumps", ISBN-3-934584-65-9. This book covers System Overview, Helix-and -port controlled distributor injection pumps, Axial-Piston Pump (VP29, VP30), and Radial-Piston Pumps (VP44).



This book is well worth buying, if you are looking for information on the care and feeding along with how it works, for the VP-44.



Another book you might be interested in also that helps in understanding the VP-44 is a book called "Diesel-Engine Management" by Robert Bosch GmbH.

The ISBN # is 0-8376-1353-1. Between these two books and the DC factory manual the information available is worth the expense.



The factory recomends between 8 and 12 psi delivery pressure. This is under ideal situations. The problem is the factory used a poor lift pump in its application. It is one of the reasons I run a FASS 150 gph with the biggest filters I can get. . I keep my pressure at 15 psi which is 1 psi above the relief overflow valves opening pressure of 14 psi. The pump does not suffer from starvation because all my lines are 3/8th ID with straight in fittings for and increase in volume. At WOT I will drop to 12 psi. Crusing down the highway in a steady state my pressure sits around 13 to 15 psi. This is what has worked for my for the last 200,000+ turns.



I ditched the factory LP before it had a chance to kill the VP.

 

[RJWEST]

Mundgyver: I probably missed it in the post,
Please , can you tell me what LP you have.
My thoughts on pressure were what you have said,
I was shooting for 10-12 psi with 10 PSI as Min.
I have installed a regulator set to 12 Psi, but still see a drop
to 5-7 psi, My guess: line drop through fuel filter ( it's clean ) and
bad LP ( holly Blue). Or dirty sock in fuel tank .

I have been reluctant to go to the High pressure LP's ( above 15PSI) as I could feel the input line ' chatter ' at idle, Did not think this was conducive for Long IP life...

 

[mhenon]

Something you should be aware of when looking at your delivery pressure from the LP is that inside the VP-44 there is a timing device that is hydraulically assisted. Too much delivery pressure and you can wind up changing the VP's ability to perform it's function. Thats why volumn of flow is more important than pressure. Too much pressure causes hydraulic lock problems and too little volume causes starvation. By increasing the delivery volumn while keeping the pressure optomized to the pumps ideal feed pressure will prevent starvation and will allow the pump to use as much fuel as it wants to without being forced to.



It is a balancing act.



This information is available in "The Bosch Yellow Jackets Edition 2003, Tistributor-Type Diesel Fuel-Injection Pumps", ISBN-3-934584-65-9. This book covers System Overview, Helix-and -port controlled distributor injection pumps, Axial-Piston Pump (VP29, VP30), and Radial-Piston Pumps (VP44).



This book is well worth buying, if you are looking for information on the care and feeding along with how it works, for the VP-44.



Another book you might be interested in also that helps in understanding the VP-44 is a book called "Diesel-Engine Management" by Robert Bosch GmbH.

The ISBN # is 0-8376-1353-1. Between these two books and the DC factory manual the information available is worth the expense.



The factory recomends between 8 and 12 psi delivery pressure. This is under ideal situations. The problem is the factory used a poor lift pump in its application. It is one of the reasons I run a FASS 150 gph with the biggest filters I can get. . I keep my pressure at 15 psi which is 1 psi above the relief overflow valves opening pressure of 14 psi. The pump does not suffer from starvation because all my lines are 3/8th ID with straight in fittings for and increase in volume. At WOT I will drop to 12 psi. Crusing down the highway in a steady state my pressure sits around 13 to 15 psi. This is what has worked for my for the last 200,000+ turns.



I ditched the factory LP before it had a chance to kill the VP.

Mundgyver, good explaination for keeping pressures at a reasonable level. More isn't necessarily better when it comes to supply pressure to a VP44.

My system pressures are almost identical to your's: 14. 5psi @ idle, 13psi @ cruise and 12psi @ WOT. I don't have a FASS but do have large diameter fuel lines, free flowing fittings and two large Fleetgauge filters. This creates a volume of pressurized fuel maybe 50 or 100 times that of an 8' length of 1/4 inch supply line. You simply can't bleed the pressure down!

The main point here is you can have too much fuel pressure. If you have to run 20+psi at idle just to maintain 6-8psi at WOT you have a severe restriction prior to the VP.

Mike

 

[DCreed]

what regulators are you guys running?

 

[CWright]

The air dog is internaly regulated.

pressure only drops to 19 at WOT.

 

[Mundgyver]

Mundgyver: I probably missed it in the post, 

Please , can you tell me what LP you have. 

My thoughts on pressure were what you have said,

I was shooting for 10-12 psi with 10 PSI as Min. 

I have installed a regulator set to 12 Psi, but still see a drop

to 5-7 psi, My guess: line drop through fuel filter ( it's clean ) and

bad LP ( holly Blue). Or dirty sock in fuel tank . 



I have been reluctant to go to the High pressure LP's ( above 15PSI) as I could feel the input line ' chatter ' at idle, Did not think this was conducive for Long IP life...

I got rid of the stock lift pump years ago. I am running an original FASS-150 GPH pump. The bueaty of this thing is that it has air seperation for the fuel which is just before the outlet to the supply line going to the VP. With the FASS set at 15 psi output I have two paths back to the tank. The first path back is the air seperation path from the FASS. The second is the Overflow valve on the VP itself which is set at 14 psi.



The FASS can easly keep up at 150 GPH potential. The result is that I get allot of recirculation of fuel back to the tank from two paths while maintaining a nice steady pressure that is within the limits of the VP.



There is someone on the Forum, and I do not remember who he is, but he does not run a lift pump at all. He has an in-bed tank with large lines that just gravity feeds the VP and he has been running this configuration for a couple of hundred thousand miles with no problem. He relies on the head pressure from the gravity weight of the fuel in the in bed tank to supply the VP.

 

[mhenon]

what regulators are you guys running?

I purchased Glaciers by-pass valve which is adjusted by internal shims. It took me a few trials with different shims but got the pressure exactly where I wanted.

Mike

 

[RJWEST]

Thanks,

Did you change any of the fittings at the IP and the Filter, to open up the lines... or leave them stock...

 

[Mundgyver]

I use my stock filter for my 100 gallon in-bed tank. The Fass has it's own filters which I replace once a year. The VP input banjo fuel fitting was replaced with a straight in barb fitting which I drilled out to give it a 3/8th ID. The Banjo fittings on the stock filter were also replaced with straight in fittings.



Since the in-bed tank is just for refill, I did not drill the the fittings that I installed on it.

 

[Gary - K7GLD]

When discussing observed fuel PSI, it's worth mentioning exactly WHERE that measurement is being made, right at the VP-44 (where mine is), or somewhere else in the fuel system.



I've always figured that since most of these fuel system efforts are being made to benefit the VP-44, THAT is the point to measure the PSI IT sees, not the fuel filter or some other relatively distant point that can easily be at a significantly different PSI than what it is seeing...

 

[Mundgyver]

Agreed. Longer lines = resistance to flow = reduced pressure. So measurements are and should always be taken close to the VP.



Anytime a fuel system is set up, care should be taken in the design and routing to keep reliability and simplicity as key factors for trouble free function.

 

[wlowe]

what regulators are you guys running?

I recently installed an aeromotive 13301 fuel pressure regulator, got it from Summit Racing. Quite a few members are using it so I made it my choice also. I've got it set for 14. 5 psi. Works great. I mounted it in the engine compartment for easy adjustments. Was also a good spot to plumb in my fuel pressure sender. The return line is attached to the fuel tank filler hose using an adapter from Glacier diesel.

 

[DCreed]

thanks for the reply and pic! is that your lunch on the fuse box? LOL!