Fuel Pressure Specification For Bosch VP44 Injection Pumps

Discussion in 'VP44 Pump' started by Mopar1973Man, Dec 26, 2011.

  1. Mopar1973Man

    Mopar1973Man Senior Member

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    Aug 22, 2011
    New Meadows, Idaho
    Ram Year:
    1996, 2002
    1996 Dodge 1500 (V8-5.9L) & 2002 Dodge Ram 2500 (5.9L Cummins)
    Fuel pressure

    Keep it in the GREEN!

    Normal fuel pressure should float about 14-15 PSI running down the pavement. Should never fail below 10 PSI at all. Here is a colorize fuel pressure gauge to give you a clue of the fuel pressure span you want. You want the needle to stay in the green at all times. Yellow zone is a warning that you should check the fuel filter, lift pump performance, overflow valve, etc.
    This is undocumented maximum pressure is 20 PSI. Now take notice to the overflow valve is set for 14 PSI so excessive pumping of fuel does nothing for performance except create more heat for the fuel, which in turns reduces the cooling ability of the fuel and adds more stress to the lift pump. So a little extra fuel pressure is a good thing because it insures the Bosch VP44 injection pump stays cooled and lubricated properly. But excessive fuel pressure will heat the fuel and reduced the cooling ability of the fuel.
    Now always remember that the only lubrication the Bosch VP44 injection pump will see is the fuel itself so if you don't have enough fuel pressure it will cause damage to the Bosch VP44 injection pump. It's like the same as running the engine with low oil pressure it will continue to run but the damage to the engine will occur. Or in this case the Bosch VP44 injection pump which happens to be about $1,200 to replace.

    Pressure Drop

    Amount of fuel pressure drop between idle and wide open throttle. 2-3 PSI drop from idle to WOT is normal. But 5 PSI or more pressure drop from idle to WOT is pointing out a failed lift pump, plugged filter, and/or plumbing restrictions.


    Best way to show this example of restrictions is lets say you house is on fire. You know your garden hose has 80 PSI of pressure but the garden hose is only 5/8" ID hose. Your wife calls 911 and gets the fire department coming in the meantime you keep fighting the fire with your little 5/8" garden hose and losing the battle. The fire department shows up and pulls a 2 1/2" hose off the truck and charges it at 80 PSI and now winning the battle. Your fire is put out! What is so different? No matter what the size of the fuel line will dictate how much volume can be pushed through the fuel line. Like the story above the water pressure was the same at 80 PSI but the hose size jumped from 5/8" to 2 1/2" ID hose and the volume changes is size of hose. So the same thing applies to the stock fuel system. The stock banjo bolts and 6mm ID pipes are just too restrictive and cannot supply enough volume of fuel for that Bosch VP44 injection pump demands. This why I highly suggest you go up to 1/2" ID plumbing.

    Additional Information (About Performance Crowds & Fuel Pressure)

    I've seen several times where people will link back to performance pump builders and quoting where they say, "(Un-named) proved that 5 PSI, under load, made all the horsepower the VP44 pump could make, even with stock fuel lines, fittings and supply pump." This might be true but there is nothing ever said about the life span of the pump at these conditions. So.. Please do not follow these performance crowds into destroying a perfectly good Bosch VP44 injection pump.
    The fact still remains from Bosch the actual designer of the Bosch VP44 injection pump states that injection pump should return 70% of the fuel back the to the fuel tank for cooling and lubing purpose of the VP44. Being the only way a Bosch VP44 injection pump can do this is to have fuel pressure above 14 PSI to open the overflow valve. Then if the stock Bosch VP44 injection pump with a enhancement box say a Edge Comp on 5x5 can consume 15-20 GPH that means the stock 35 GPH pump cannot keep up with Bosch's design of 70% return volume. So this why products like AirDog, Raptor and FASS was created because they actually meet the demands of the Bosch VP44 injection pump. Then another fact that Bosch will let you know of is that diaphragm damage occurs from from operating the Bosch VP44 injection pump at low fuel pressures. Making matters worse is that no Bosch injection re-builder will warranty a VP44 injection pump with diaphragm damage. Dead give away that you had a bad lift pump or low fuel pressure problems.
    Then the other fact is right from the Dodge Factory Service Manual has the minimum fuel pressures (picture at the top of the page). It even states the pressure that the overflow valve requires to open. Refer back to Overflow Valve Testing from the Dodge Factory Service Manual and see that the overflow valve should remain closed at 10 PSI and open by 14 PSI. So if the overflow valve is close by 10 PSI then you extra cooling and lubrication just disappeared.
    So ultimately it suggested to have a fuel system of no less than 100 GPH supply that can maintain a minimum pressure of 14-15 PSI at WOT. This will great extend the life of the VP44 because it keeps the electronics cooler longer and keeps the rotating parts lubricated properly.
    So please people let the facts and information from the actual designers of the injection pump (Bosch) and engine (Cummins) provide you proper information for your fuel system for your engine. Don't be swayed by performance shops claim of high horse output with little fuel pressure. As I proved right here is doesn't work for longevity of the VP44 injection pump...

    Here is good fuel pressure Excuse my air bubble sloosh on the return trip! I was low on fuel... This is common for the old school drawstraws.
    Fuel pressure testing - YouTube

    Here is a bad lift pump, suction restriction, plugged fuel filter. Anytime the fuel pressure falls under 10 PSI is a instant fail.
    07 22 11 - YouTube

    Then more on fuel system of the 24V Cummins.
    Cummins_ISB.mp4 video by TannerSpangler1 - Photobucket

    Orignal Article here...
    Mopar1973Man's Dodge Cummins Articles - Fuel Pressure Specification For Bosch VP44 Injection Pumps
    Last edited: Dec 26, 2011
    Cummins Powered likes this.
  2. res8856

    res8856 Junior Member

    Likes Received:
    Mar 20, 2015
    Ram Year:
    cummins diesel
    vp44 fuel pressure

    I saw your article about the fuel pressure specification for Bosch VP44 Injection Pump and the specification from the Dodge Factory Service Manual showing a minimum of 10 psi with the engine running. Does Dodge have a published specification showing a maximum allowable fuel pressure for this pump in their manual? if so, can you post it? Thanks.
  3. Weezer

    Weezer Senior Member

    Likes Received:
    Oct 18, 2015
    Ram Year:
    Hemi 5.7
    [​IMG]ds.tapatalk-cdn.com/20160828/229d373ec5a7fba 59d3a08ff0da32427.jpg[/IMG]
    6 the

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