Choosing The Right Fuel Lift Pump For My Needs

[JAG1]

Has anyone found Bosch's specs on Maximum fuel pressures allowed? Like to know where the 19-20 as tops came from as I have regulators on new Raptor 150's that cannot stay in range unless turned up a bit more.

[Mopar1973Man]

Because the return port in the VP44 is too small for higher pressure and could possibly push the front seal out. Rare but has happened. Return is on the left.

 

[dripley]

21 hours ago, Tractorman said:

Actually, it is not odd.  There is a fixed displacement vane pump inside the VP44 injection pump.  This vane pump rotates at the same rpm as the VP44 and provides fuel flow for cooling of the VP44 as well as some other duties.  The internal vane pump provides much more fuel than is being consumed by the injectors.  Consequently, the fuel pressure rises internally and the excess fuel is forced over a relief valve that is set at over 100 psi (not sure of the exact pressure) and the fuel is returned to the suction side of the internal vane pump.  The inlet of the 14 psi relief valve is in common with the outlet of the internal vane pump (operating at more than 100 psi), so there is always fuel flowing over the 14 psi relief valve regardless of the lift pump pressure.

If I am reading this right you are saying the internal vane pump is where the pressure comes from to open relief valve and not the lift pump.

 Many years ago after receiving the in tank pump from Dodge I started having some bucking and dead pedal issues. Took to a diesel shop in Maryland that some time trying to find the issue. The only thing they found was low fuel pressure, 5 psi at idle and near 0 at WOT. I added a booster pump on the frame and it cured the issues I was having. I have no idea what pressure I had since I had no FP gauge nor knew of the need for one. I was pretty ignorant as to what made this truck back then,

[Tractorman]

1 hour ago, dripley said:

If I am reading this right you are saying the internal vane pump is where the pressure comes from to open relief valve and not the lift pump.

 

Yes, that is correct.  The internal vane pump generates more flow than can be used by the combination of supplying fuel for the injectors, internal control circuitry, and fuel flowing over the 14 psi relief valve returning to the tank regardless of any fueling demands.  Because more flow is being generated than can be used, the pressure must rise to the relief pressure of the internal vane pump (over 100 psi) and flow the remaining fuel to the suction side of the internal vane pump.

 

The lift pump must always generate more flow than the combination of the fuel being consumed by the injectors and the fuel being returned to the fuel tank from the VP44.  If the lift pump does its job, there will always be a positive fuel pressure reading at the test port.  The remainder of the fuel flow from the lift pump will flow over an internal lift pump relief valve and either return to the suction side of the pump or return to the fuel tank via a separate line.

 

2 hours ago, dripley said:

Many years ago after receiving the in tank pump from Dodge I started having some bucking and dead pedal issues. Took to a diesel shop in Maryland that some time trying to find the issue. The only thing they found was low fuel pressure, 5 psi at idle and near 0 at WOT. I added a booster pump on the frame and it cured the issues I was having. I have no idea what pressure I had since I had no FP gauge nor knew of the need for one. I was pretty ignorant as to what made this truck back then,

 

I don't have an explanation for this situation as there are some unknowns here and as you said this happened many years ago.  It is possible that under wide open throttle, there were disruptions of fuel flow that the test gauge didn't show.  Any disruption of fuel flow could cause bucking.  When you added the booster pump, that could have masked the true flow problem and made the symptoms disappear.  Just speculation on my part.

 

It is very interesting that you mention this, because I am experiencing a similar condition, but only when towing up a continuous grade with a steady throttle, and not at full power.  This symptom has appeared after installing new RV275 injectors.  Our definition of bucking could be different, but I am going to try to figure out what is going on and I may even get to the point of adding another lift pump in series just to see if the symptoms disappear.  If I do this, I will post the results.

 

- John

[dripley]

5 hours ago, Tractorman said:

It is very interesting that you mention this, because I am experiencing a similar condition, but only when towing up a continuous grade with a steady throttle, and not at full power.  This symptom has appeared after installing new RV275 injectors.  Our definition of bucking could be different, but I am going to try to figure out what is going on and I may even get to the point of adding another lift pump in series just to see if the symptoms disappear.  If I do this, I will post the results.

The bucking I experienced was very much like the engine shutting down for split second. A pretty jolt. Mostly when I was towing like you mention or a WOT run at higher rpm empty. It happen to me before the oe VP crapped out at 75k. A filter chznge cured that though. Who da thunk you have change those things. A filter change did not however cure the problem after the intank pump was installed but the booster pump did. I ran that set 3 or so years before installing the AD. I came across it today while digging out the rear lifting ring for the head.

That is a BD Diesel booster pump from 11 years ago.

Edited March 27, 2019 by dripley

[Mopar1973Man]

Boy, I remember those days long ago... Been there done that... 

 

[Mad Bomber]

full meal deal FASS

[Evan]

I did the raptor 150 and plumbed from the tank to injection pump. Snake river diesel put together a kit because I had to remove the factory retrofit pump from the tank. 

My Raptors on the frame rail. 

I idle at 20 and drop to about 15 pulling a steeper hill towing. Empty the needle doesnt drop very much below 20.

 

It's been on about 8 years I think. I've raised pressure 3 or 4 times to maintain 20 at idle.

Very damn nice truck