VP44 Injection Pump Teardown - How it Works

[Tractorman]

4 minutes ago, wil440 said:

The main return from the pressure regulator uses the old fuel supply line into the basket, the T return was to start with the original line going to the basket until that cracked near the trans, it is now 3/8th rubber but still goes to the basket onto it's original connection

 

So, If I am understanding correctly, you have two fuel returns entering the basket.  Where does your lift pump pull fuel from inside the fuel tank?

 

- John

[wil440]

1 minute ago, Tractorman said:

 

So, If I am understanding correctly, you have two fuel returns entering the basket.  Where does your lift pump pull fuel from inside the fuel tank?

 

- John

Yes John that is correct, 2 returns main one from the fuel pressure regulator goes to the old fuel supply line connection and the T is onto it's original connection both at the basket

I have a draw straw into the basket for fuel supply

[Dieselfuture]

All of my fuel gets returned to the basket too, fuel gets pretty warm in summer when tank gets to last 5-10 gallons around 160f when I fill the tank up it'll drop to 110 or so. I'll try to reroute lift pump return to filler neck I still have the T installed there with a cap on. If the hose is long enough if not I'm not too worried about it as it's been this way for about 10 years. Like been mentioned before fuel has got to get to at least 160 that runs through the head and gets returned to the basket. But we're debating several things here, cooling of vp and asphaltines. I'm not worrying about asphaltines as I never had an issue with it running my temperatures and really I'm not too worried about vp cooling as I believe revised pumps don't have hardly any issues with solder as old ones did. Lubrication is probably more important then the other two issues for longevity, just my 

[dripley]

16 hours ago, wil440 said:

Yes John that is correct, 2 returns main one from the fuel pressure regulator goes to the old fuel supply line connection and the T is onto it's original connection both at the basket

I have a draw straw into the basket for fuel supply

Same as mine is set up.

 

9 hours ago, Dieselfuture said:

All of my fuel gets returned to the basket too, fuel gets pretty warm in summer when tank gets to last 5-10 gallons around 160f when I fill the tank up it'll drop to 110 or so. I'll try to reroute lift pump return to filler neck I still have the T installed there with a cap on. If the hose is long enough if not I'm not too worried about it as it's been this way for about 10 years. Like been mentioned before fuel has got to get to at least 160 that runs through the head and gets returned to the basket. But we're debating several things here, cooling of vp and asphaltines. I'm not worrying about asphaltines as I never had an issue with it running my temperatures and really I'm not too worried about vp cooling as I believe revised pumps don't have hardly any issues with solder as old ones did. Lubrication is probably more important then the other two issues for longevity, just my 

I cant agree more with this. We are set up the same way and for about the same time. My last VP that lasted 265k ran its entire life on this set up and either 2 stroke or bio blend diesel. Never had any trouble running the fuel level down very low.

 

Just to add I have stated that pump ran 275k but looking it was only 265k.

[Tractorman]

 

VP44 Injection Pump Fuel Return Flow Test

 

A bit of history – the first VP44 injection pump on my truck failed (code 0216) and was replaced under warranty along with the engine block-mounted lift pump which was also replaced under warranty with an in-tank lift pump in August of 2005 at 87,000 miles.

 

The old block-mounted lift pump was still providing 12 psi at idle and 7 psi at wide open throttle when it was replaced. The new in-tank lift pump provided 6 psi at idle and 3 psi at wide open throttle.  I ran that lift pump for 164,000 miles.  In April of 2016 at 251,000 miles on the truck, I removed the in-tank lift pump and installed a used FASS DRP-02 frame mounted lift pump.  The in-tank lift pump was still working fine – I just wanted the lift pump to be easily accessible if it failed on a road trip.  The FASS lift pump provides 12 psi at idle and 6 psi at wide open throttle. 

 

Currently, there is approximately 106,000 miles logged on the used FASS DRP-02 lift pump.  The current replaced VP44 has logged just under 270,000 miles.

 

As many of you probably know by now, I am a firm believer that the only job for the lift pump is to flow enough fuel to provide a positive pressure at the inlet of the VP44 injection pump under any operating condition.  And because I believe this to be true, I have never been concerned about lift pump fuel pressure being low – example: 3 psi at wide open throttle.

 

By design I believe the OEM lift pump produces more flow than the VP44 injection pump and injectors will ever consume under any operating condition which means that there will always be a positive pressure at the inlet of the VP44 injection pump.  It is also my understanding that when fuel enters the VP44 injection pump - that fuel flows directly into the inlet of the internal vane pump inside the VP44 injection pump.  From this point forward it is the internal vane pump that determines the flow and the maximum operating pressure to provide fuel flow for charging the fill chamber for high pressure injection, fuel flow for hydraulic operation of the timing piston, and fuel flow over the 14 psi overflow valve that returns fuel back to fuel tank for cooling the injection pump.

 

The tests. 

 

I have performed several fuel return flow tests from the VP44 fuel injection pump.  The purpose for the tests is to show that the volume of fuel returning to the tank (from the VP44 and injectors) does not change whether the lift pump is operating or not operating.  To demonstrate this I made one small modification (which will be a permanent modification on my truck) to the supply fuel line.  I added a fuel line with a one-way check valve in parallel which bypasses the frame-mounted lift pump.  The added fuel line and one-way check valve will allow for free flow of fuel around the lift pump should a lift pump failure occur.  During normal lift pump operation the one-way check valve will remain closed.  The photo below shows the fuel supply diagram for my truck.

 

 

For the tests I used a one-gallon oil jug with volume markings at one-quart intervals.  I used a helper and started the clock on the 1 quart mark on the jug and stopped the clock on the 3 quart mark on the jug.  The total volume returned for each test was .5 gallons of fuel.

 

My truck is a 2002 2500 with a NV5600 transmission.  The fuel lines are stock diameter, the fuel filter is the OEM filter inside the filter housing mounted on the engine, and the lift pump is a used frame mounted FASS DRP-02 that probably flows somewhere around 65 GPH.

 

I performed the tests as follows:

 

Test #1:  engine at idle, fuel transfer pump operating - .5 gallons pumped in 92 seconds

Test #2:  engine at idle, fuel transfer pump operating - .5 gallons pumped in 94 seconds

 

Average fuel pumped is .5 gallons in 93 seconds = .3225 gpm rounded to .32 gpm or 19.35 gph

 

Test #3:  engine at idle, fuel transfer pump disabled   - .5 gallons pumped in 93 seconds

Test #4:  engine at idle, fuel transfer pump disabled   - .5 gallons pumped in 95 seconds

 

Average fuel pumped is .5 gallons in 94 seconds = .3191 gpm rounded to .32 gpm or 19.35 gph

 

Test #5:  engine at 2000 rpm, fuel transfer pump disabled   - .5 gallons pumped in 64 seconds

 

Fuel  pumped is .5 gallons in 64 seconds = .47 gpm or 28.1 gph

 

The averaged test results from Test #1 and #2 (lift pump operating) clearly show that there is no significant volume change when compared to the averaged test results from Test #3 and #4 (lift pump disabled).  My conclusion is that lift pump pressure is not relevant to fuel returning from the VP44 injection pump and injectors.

 

The result of Test #5 clearly shows that return flow volume increases with engine rpm, even with lift pump not operating.

 

I performed one other test.  Since I am convinced that it is the internal vane pump that does all of the work, I disabled the lift pump and drove my truck to town and back – a 25 mile round trip.  I accelerated and held 30 psi boost several times. I restarted the truck several times while running errands.  The engine never stumbled and continued to deliver the power it always does.  I am not diminishing the importance of the lift pump function, but I will now worry less should I have a lift pump failure while on a trip.   I will just keep driving until I get to a convenient place to replace the pump.

 

My overall conclusion is that requiring lift pump pressure to always be above 14 psi or the VP44 injection pump will be sacrificed is now a busted myth.  There, I have said it.   Of course, each person is entitled to draw his / her own conclusion.

 

One last note…, I know that the VP44 on my truck can fail at any time, but it has already provided a long life, even operating under the parameters of RV275 hp injectors and a Smarty tuner with fuel duration set at 5.  I know this will be hard to believe for some, but this VP44 has never seen any lift pump pressure higher than 12 psi, and that 12 psi is only at idle – most of the time it is operating at a far less pressure.

 

The following photos show the volume of fuel returning to tank under specific conditions:

 

 

 

 

-  John

 

 

 

Edited July 4, 2021 by Tractorman

[wil440]

Your first picture of the return flow is what I saw while testing mine with the return back into the filler, I didn't measure as you have done because for 1 I didn't have the time and 2 once I saw what was returning I wasn't concerned anyway, mine was at idle and only went up with RPM due to crank driven FLP, my idle pressure is around 5 to 7psi with over 20psi around 2k rpm and rising

[Great work!]

@TractormanI agree there is a lot of hype about lift pumps. Probably because of all the warranty claims early in the life of these trucks. However I believe that inside the vp is a very violent and turbulent place and a lift pump keeps some pressure in there to prevent cavitation. 

 

The timing piston oscillilates in it's bore causing wear because the rollers have resistance and want to drag the cam ring with them. Just speculating that there needs to be some pressure on BOTH sides (vane pump side and lift pump side) of the timing piston to dampen it. That could be why so many stuck pistons happened when lift pumps failed.

 

[Mopar1973Man]

Agreed. I don't rely on the internal vane pump to keep up with the demands either. This is why there has to be some positive pressure. 

 

10 minutes ago, Great work! said:

That could be why so many stuck pistons happened when lift pumps failed.

If you seen the timing piston in the VP44 I've got you'll see a very galled up piston plus the bore. This particular case it was more a lubricity failure also could be from low fuel pressure since fuel will heat up in the pump without good return flow so now the fuel thins out and the parts start to wear. 

 

[Tractorman]

36 minutes ago, Great work! said:

However I believe that inside the vp is a very violent and turbulent place and a lift pump keeps some pressure in there to prevent cavitation

 

Just to be clear, I have always believed that there should be a positive pressure at the inlet of the VP44.  That is why a lift pump is necessary.  The timing piston failed on my original VP44 at 67,000 miles (replaced VP44 at 87,000 mi).  The lift pump pressure was always within specifications during that time period.  I believe the timing piston failures at that time were due to inferior timing piston and bore material quality because Bosch corrected those issues in their remanufactured VP44 injection pumps without stating to the public that there were issues with them.

 

I appreciate your input.

 

36 minutes ago, Mopar1973Man said:

f you seen the timing piston in the VP44 I've got you'll see a very galled up piston plus the bore. This particular case it was more a lubricity failure also could be from low fuel pressure since fuel will heat up in the pump without good return flow so now the fuel thins out and the parts start to wear. 

 

The results of my test show that return flow remains the same regardless of lift pump pressure.

 

- John

 

[Mopar1973Man]

17 minutes ago, Tractorman said:

The results of my test show that return flow remains the same regardless of lift pump pressure.

 

Hmmm... Just to challenge this quote a bit. Ok, then please explain with my typical 15 to 17 PSI lift pump pressure (AirDog 165) I'm typically 10*F to 15*F cooler in fuel temp over most with a stock lift pump or weak lift pump? My typically fuel temp is about 110*F to 140*F maximum. There are members here with fuel temps much higher at 150*F to 160*F. Being most claim the VP44 take a huge amount of heat soak from the block. Still I have cooler fuel temps. Keep in mind I've been seeing 105*F to 118*F temperatures here locally for outside temps.

 

Edited July 4, 2021 by Mopar1973Man

[wil440]

My fuel temp never gets to 120F ever, most of the time it's less than 110F  5 to 7 psi at idle  20 plus at 2k  

[Tractorman]

3 hours ago, Mopar1973Man said:

Hmmm... Just to challenge this quote a bit. Ok, then please explain with my typical 15 to 17 PSI lift pump pressure (AirDog 165) I'm typically 10*F to 15*F cooler in fuel temp over most with a stock lift pump or weak lift pump?

 

It could be very possible that "most with a stock lift pump" also have a stock fuel basket which means that hot fuel is being returned right next to the suction in the fuel basket.  That alone would make a huge difference in the fuel temperature as the lift pump would be drawing in returned fuel that is much hotter than the rest of the fuel in the tank.  

 

If I recall correctly the fuel return line on your truck does not enter the fuel basket.

 

- John

[Mopar1973Man]

17 hours ago, Tractorman said:

If I recall correctly the fuel return line on your truck does not enter the fuel basket.

 

Backwards... My injector return and VP44 return arr both in the fuel basket.

 

I draw from the fuel tank directly. Never from the basket. Like I said I've been having 105 to 118*F weather here in Riggins, ID. Still can keep the fuel temps lower than most. As seen on the overhead of my 2006 Dodge I ran last Friday... Normal never run the tank below 1/2 a tank for better cooling too. Below 1/2 tank you can start to see a climb in fuel temps.

 

 

Very stable 15 o 17 PSI fuel pressure from idle to WOT at 100 MPH on a AirDog 165 pump with a AirDog 150 filter body. 

 

[Tractorman]

17 hours ago, Mopar1973Man said:

Backwards... My injector return and VP44 return arr both in the fuel basket.

 

I draw from the fuel tank directly.

 

Okay, I got it backwards.  The point is, the fuel supply to the VP44 is separate from the fuel return from the VP44 / injectors on your truck..  That is why your fuel temperatures run cooler than most.

 

Are saying that you believe your AirDog 165 lift pump (15 to 17 psi) is providing more return fuel from the VP44 / injectors than a stock lift pump?  Because, if you are, then this is where we may have to agree to disagree.

 

The point of my testing is to show that fuel cannot be forced through the fixed displacement vane pump in the VP44, regardless of lift pump pressure or lift pump volume.  The lift pump pressure is 12 psi in Test #1 and #2 and 0 psi in Test #3 and 4. The return fuel flow volume did not change regardless of lift pump pressure.

 

On 7/3/2021 at 9:32 PM, Tractorman said:

Test #1:  engine at idle, fuel transfer pump operating - .5 gallons pumped in 92 seconds

Test #2:  engine at idle, fuel transfer pump operating - .5 gallons pumped in 94 seconds

 

Average fuel pumped is .5 gallons in 93 seconds = .3225 gpm rounded to .32 gpm or 19.35 gph

 

Test #3:  engine at idle, fuel transfer pump disabled   - .5 gallons pumped in 93 seconds

Test #4:  engine at idle, fuel transfer pump disabled   - .5 gallons pumped in 95 seconds

 

On 7/3/2021 at 9:32 PM, Tractorman said:

 

Average fuel pumped is .5 gallons in 94 seconds = .3191 gpm rounded to .32 gpm or 19.35 gph

 

The diagram below shows a general concept of how I believe the fuel system works.  This diagram only represents my idea of how the VP44 fuel system works.

 

- John

 

 

 

Edited July 6, 2021 by Tractorman

[Mopar1973Man]

Best I can add to this is according to the Bosch EFI documentation I last seen was the VP44 required like 60% return flow for optimal cooling and lubing. 

 

Then just for fuel consumption values. For 20 MPG you'll used roughly 2.75 GPH. For faster speeds like 70 to 80 MPH can be upwards of 4 to 5 GPH burned. Return rates will change over engine load and fuel demands. 

 

Just for fun, I've seen full WOT operation as high as 22.0 to 25.0 GPH burned! Return rates will be at it lowest point now.

Edited July 6, 2021 by Mopar1973Man

[LorenS]

I use a type A lift pump, so that may be one reason my fuel gets HOT, like 160, on long runs, even empty and not towing. Coupled with fuel return to basket.

 

Fuller tank of fuel only slows the temp rise.

[dripley]

I cant check my fuel temp but the truck has run with both returns and the pickup in the basket for 10 years. All of that on the VP that went 275k. Got about 60k on the replacement. I hope this one likes it as much as the last one.

[Tractorman]

The three diagrams below (A, B, and C) show low pressure fuel flow inside the VP44 injection pump.  The purpose of the diagrams is to show what I believe is going on inside the VP44 pump, specifically, the role of the internal vane pump. 

 

The flow to the injectors, the overflow valve, and other various internal VP44 components is supplied by the internal vane pump, not the lift pump. 

 

The flow rate value that I chose for the internal vane pump is based on my return flow rate shown in one of my previous posts.  That test shows that the engine at idle returns 19 gph to the fuel tank.  Based on this number, I assigned 22.5 gph for vane pump output in Diagram A.  This equals 13 cubic inches of fuel per one vane pump revolution.  There are 400 vane pump revolutions per minute when engine is idling at 800 rpm. There are 231 cubic inches in one gallon of fuel.

 

A couple of things worthy of mention:

 

From Jeeper Jimmy a few years ago,

 

The first thing the incoming fuel sees in the VP44 is a vane-type fuel pump (called by Bosch the ‘Internal Fuel Pump’) which raises the pressure to “8 – 22 bar (116-319 PSI) depending on the application and RPM” (direct quote from VP44 Service Manual and Bosch Fuel Injection Pump Manual).

 

From the FSM (2002),

 

A greater quantity of fuel is required for cooling the VP44 than what is necessary for engine operation. Because of this, approximately 70 percent of fuel entering the pump is returned to the fuel tank through the overflow valve and fuel return line.

 

You will find that fuel return flow exceeds 70% of fuel entering the pump in all three diagrams.

 

  Circuit A - 95% of fuel is returned

  Circuit B - 93% of fuel is returned

  Circuit C - 80% of fuel is returned

 

There may be errors in my calculations - please let me know if something does not make sense.  

 

-  John

 

Edited July 13, 2021 by Tractorman
'cause I couldn't get it right the first time.

[dripley]

There is that pesky picture problem again. Or at least I cannot see them.

[Threadzy]

12 minutes ago, dripley said:

There is that pesky picture problem again. Or at least I cannot see them.

Nether can I.