VP44 Injection Pump Teardown - How it Works

[Mopar1973Man]

Just to say this my first adventure with my diesel was a failed lift pump pumping a mere 7 PSI and shortly after that P0216 code. This was the beginning of my website back in 2004. The first article I made. All covered under warranty. From that point upgraded stuff and never looked back. My second VP44 failed after 247k miles and a P0216 code but stuck in full advancement. Still running on my 3rd pump at 432k miles. Even the Dodge FSM states 10 PSI minimum.

[Great work!]

I dug deeper into my spare test pump and need to correct one of my prior statements. It's not just the leakage and lube that get returned to the tank.

When the spill valve closes injection occurs AND the vane pump port in the rotor gets routed to the port directly ahead of it which goes to the overflow banjo bolt. The bore in the center of the rotor enlarges very slightly where the spill valve exits so that some fuel gets by and cools the solenoid. The rotor also has lube holes so that flow comes out the end of the rotor. The end chamber where the injection solenoid is has a port with a small orifice pressed into it that flow also goes to the overflow. In the pic the ports are drilled at a slant and meet at the tapered part of the spill valve. So the vane pump gets routed to the tank when an injector is spraying. When the spill valve is de-energized at the EOI the three plungers are still moving inward so that flow is shot back towards the accumularor section that is formed by the diaphragm disk.

@TractormanI agree with your explanation that the vane pump is rapidly shifted between charging the plungers and returning to tank during injection.

 

 

@wil440 I'm just speculating that the 14 psi overflow is for the benefit of the vane pump. It keeps enough back pressure on the vane pump so that at very low cranking rpm when the flow from the small displacement pump is very low there will be enough pressure differential so that the injection plungers will be charged and forced outward to follow the cam ring profile.

[LorenS]

For a given flow rate pressure correlates to restriction. Pinching off the return raises resistance so either pressure rises, flow decreases, or both. Simple DC electric circuit. I don't know the Cv value (K value in SI units?) of anything in the system, especially not that little 14PSID pressure regulator.

[MikeH]

When a rebuilt VP44 is put on the test stand what head pressure (lets say lift pump pressure) is used to fuel the system? I'm going by memory now but way back (like 2000 to 2005 or so) when we were trying to figure out how to best feed this thing one of the Bosch authorized facilities said they applied 14 PSI to the stand. Seems like we all jumped on that thinking if that's the inlet pressure the big boys are using to setup and adjust the pump, that's what we should use on our pickups. 14 psi then became the holy grail of lift pump pressure. 

[Tractorman]

12 hours ago, Dieselfuture said:

I agree but I think the debate now is what is pushing it open the lift pump or the internal vane pump, and if it is internal pump that pushes 300psi then I'm confused why bother putting in a 14psi valve  I'm trying guys give me a break

 

You pose a good question.  It is the flow from the internal vane pump that is opening the 14 psi overflow valve as soon as the engine is running.  Many VP44 industrial engine applications don't even use a lift pump, but you can bet plenty of fuel is returning to the fuel tank while the engine is running.  The internal vane pump builds pressure because its flow output is greater than the total consumption of the the fuel being used by the injectors and fuel returning to the fuel tank,  The remaining unused fuel is returned directly to the inlet of the internal vane pump through the internal vane pump pressure regulator (8 – 22 bar (116-319 PSI).  The 14 psi overflow valve is important for cooling, but because of its location and the narrow passages that supply fuel  to it, it does not impact the operating pressure needed to fill the plunger chamber by the internal vane pump.

 

From Jeeper Jimmy:

 

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). A pressure control valve at the output of the vane pump bypasses fuel back to its input to control the desired vane pump output fuel pressure and varies depending on RPM. This is a pure spring-loaded mechanical devise; it only depends on vane pump pressure, it doesn’t depend on the VP input pressure nor any electrical signal. The amount the pressure control valve opens depends on how much pressure the vane pump is producing. The vane pump is a positive-displacement pump; therefor its output flow increases pressure as RPM increases. From here on, as long as there is a sufficient volume of fuel available at the VP44 input, it doesn’t matter how much pressure the external feed pump (lift pump) is producing, the VP44’s internal pressure will be controlled at design pressure by the vane pump and the pressure regulator. Since the vane pump output pressure increases with RPM, the amount of fuel bypassed varies to allow a desired, controlled pressure which is dependent on engine RPM (the higher the RPM, the higher the pressure). This higher pressure is necessary in a radial piston solenoid valve controlled injection pump (VP44) because the same cavity of the high pressure pump (the Plunger Chamber) must be filled to a design pressure for each injection, unlike the in-line injection pump which fills each of six cavities in sequence. The higher the RPM, the less time there is to fill the Plunger Chamber, therefore the higher the pressure must be to assure proper filling of it prior to the next injection.

 

@Great work!, thank you for your diligence in looking deeper into the internal vane pump and overflow valve operation.

 

- John

 

[wil440]

8 hours ago, Mopar1973Man said:

Just to say this my first adventure with my diesel was a failed lift pump pumping a mere 7 PSI and shortly after that P0216 code. This was the beginning of my website back in 2004. The first article I made. All covered under warranty. From that point upgraded stuff and never looked back. My second VP44 failed after 247k miles and a P0216 code but stuck in full advancement. Still running on my 3rd pump at 432k miles. Even the Dodge FSM states 10 PSI minimum.

I fully understand what you say and what has been recommended but things change.... earth was thought to be flat and the centre of the universe once.

If you remember I got into testing return flow because I was bothered about 5 to 7psi on a mechanical gauge, this is with the DTT pump, I even pulled it to peices to check if it was ok, nothing wrong with it at all, renewed the overflow just to test with a new one, no change, I then had the return line crack at a chassis bracket alongside the trans so replaced that with 3/8th rubber fuel line, bear in mind my return line from the back of the head is as it was and the fuel reg uses the old supply line, it is the line from the back of the head/VP that I checked for flow

 

Me personally If anyone is having fuel problems whether it be low pressure, high temps, failed VP  whatever I'd advise to disconnect the return at the T back left of the head and run a rubber line from that into the neck to test return BEFORE doing anything else, the line there is a push fit and a rubber line of the correct size does push over the stub it would take maybe 1/2hr to do and say 6ft of rubber fuel line, this way the state of the lift pump is known good or bad.

I don't believe every truck is the same take mine and Lorens for instance why have I got 5 to 7 at idle (20+ at 2k+)and low fuel temps and Loren is 17 and high temps, all pressure is is a measure of a restriction anyway.

Surely the correct advice is to get good quality clean cool fuel to the VP in sufficient quantity as to allow the system to send most back to tank to cool the VP.... note I didn't mention pressure.

Maybe John can spread some thought onto this Friendly debate

[Dieselfuture]

@Tractorman thanks for explaining.... I got it now  basically the biggest restriction in my mind are small fuel lines and crappy lift pumps that fail or can't keep up at higher loads and vain pump has to work extra hard to suck fuel from the tank through all the bs. So if someone mounted a fuel tank above the vp and ran a 1/2" line to the inlet you really wouldn't need a lift pump then. There would be enough pressure just because the tank is above the pump and enough flow through a bigger line that it would never cavitate. The way I see it lubrication is more of a concern then keeping 17-20 psi to the vp. I see the reasoning behind the idea of keeping good pressure to the vp just for the simple insurance that it has fuel at higher loads. That's why on normal use going down the hwy if you lose the lift pump truck keeps going, because the vane pump has no issues pooling the fuel but as soon as you step on it and load increases then the vain pump struggles to keep pooling fuel and truck stumbles and runs like crap at the same time wearing out internals because lack of lubrication of possible entrained air. 

Clear as mud, just kidding I think I got it, thank you all 

@Mopar1973Man @wil440 could it be that earlier pumps were failing with low fuel pressure because of all the revisions that haven't been done yet or is it possible that people were seeing 7psi when looking at it at idle or going down the road with no load and not under load where under load there was no pressure and damage was happening. Otherwise these stories contradict each other on how some get away with 5-7 psi lift pressure and have well over 250k on pump some even original. 

4 hours ago, wil440 said:

fully understand what you say and what has been recommended but things change.... earth was thought to be flat and the centre of the universe once

Lately I've been looking into all of these crazy subjects and more I look at them the more I'm not sure what is true anymore, it seems that most of what we're told is a lie 

[LorenS]

4 hours ago, wil440 said:

 

I don't believe every truck is the same take mine and Lorens for instance why have I got 5 to 7 at idle (20+ at 2k+)and low fuel temps and Loren is 17 and high temps

I wonder if my DRP is heating the fuel. That style doesn't have a return to the tank, it only dumps excess back to the suction side. Coupled with return to the fuel basket, that fuel is getting churned a lot.

33 minutes ago, Dieselfuture said:

these stories contradict each other on how some get away with 5-7 psi lift pressure

Wil440's 5-7 is from a mechanical lift pump when the engine idles. At a higher RPM his pressure should rise until the lift pump's regulator starts to divert fuel. If a guy was to really lug the engine, this may not be a good approach. Driven at moderate RPM and higher, it should work beautifully.

 

Last time I looked to buy a mechanical pump none of the regular sources had any.

 

I wonder how much the fuel temp rises as it goes through the head, and does that passageway get clogged with asphaltenes in higher mileage, stock head trucks (particularly those abused by previous owners...).

I need to check my return flow to find out!

[wil440]

44 minutes ago, LorenS said:

I wonder if my DRP is heating the fuel. That style doesn't have a return to the tank, it only dumps excess back to the suction side. Coupled with return to the fuel basket, that fuel is getting churned a lot.

Wil440's 5-7 is from a mechanical lift pump when the engine idles. At a higher RPM his pressure should rise until the lift pump's regulator starts to divert fuel. If a guy was to really lug the engine, this may not be a good approach. Driven at moderate RPM and higher, it should work beautifully.

 

Last time I looked to buy a mechanical pump none of the regular sources had any.

 

I wonder how much the fuel temp rises as it goes through the head, and does that passageway get clogged with asphaltenes in higher mileage, stock head trucks (particularly those abused by previous owners...).

I need to check my return flow to find out!

my fuel pressure pegs at about 22 to 25, it is only idle that is 5 to 7, any and I do mean any rpm's over idle sends it up and fast, I would have to check but IIRC there is 2 returns with the DTT pump, one from the back of the head which is the Head and VP and one from the reg which is the system in general.

As for low rpm and temps, due to fuel cost here I lug my truck all day every day, motorway driving I'm 1100 to 1500 all the time, it just ambles along nice (we don't have all that many big grades here), I drive watching rpm, speed, trans and egt's, I work for myself paid travel so I'm in no rush at all and we have speed cameras everywhere

My fuel goes to the basket at present, I have the parts made to stick it in the filler but not done it yet

[MikeH]

40 minutes ago, LorenS said:

I wonder if my DRP is heating the fuel. That style doesn't have a return to the tank, it only dumps excess back to the suction side. Coupled with return to the fuel basket, that fuel is getting churned a lot.

"it only dumps excess back to the suction side"    Loren. my mutant/hybrid DIY home built fuel system created too much pressure (like 26psi) when I first put it together. The advice at the time was to get the pressure back to the magic 15psi so I installed a Glacier bypass check valve AFTER the lift pump and filters which returned the excess fuel to the filler neck...not back to itself or the fuel basket.

Not sure how this setup has played in the longevity of my LP or VP but it's been going strong for ~15 years now. 

[Tractorman]

1 hour ago, LorenS said:

I wonder if my DRP is heating the fuel. That style doesn't have a return to the tank, it only dumps excess back to the suction side. Coupled with return to the fuel basket, that fuel is getting churned a lot.

 

I think you are on to something here.  I just recently rerouted the return fuel from the VP44 and head to the filler neck on my truck.  Previously it returned  into the same  basket that the lift pump suction drew from.  Before rerouting the fuel return, on road trips I would stop and put my hand of the on the FASS DDRP02 lift pump (modified for a frame mount} and the pump housing would be hot to the touch - I estimated to be about 140 degrees (ambient air temperature was 80 degrees) because I could only hold my hand on it for a few seconds before it became too uncomfortable.  This was with a full tank of fuel.  

 

Yesterday, I had an opportunity to check the lift pump temperature by my hand with the rerouted fuel return line.  I purposely ran the fuel tank down to less that 1/4 tank while towing my trailered tractor over 200 mils at 65 mph  - combined weight of 16,000 lbs.  I stopped at a rest area just before refueling and placed my hand on the lift pump.  Much cooler, probably around 110 degrees with ambient air temperature at 75 degrees.  I filled the tank about 10 miles and 30.1 gallons later - the lift pump still running cool just before fill up which means there was only about 5 gallons of fuel left in the tank that was cooling the returned fuel.  This test clearly shows the results of simply getting the return fuel flow out of the basket.

 

- John

 

 

[wil440]

As I have everything made to put my return into the neck I'll get on it and get it done and see what happens to my temps but as I said my fuel temps are low, highest I ever saw was 118F last summer towing my 5th back from Cumbria (North West England right on the Scottish border) 300 miles or so and that was 20 mile from home through a hilly built up area (City)

 

My temps are usually sub 100F easy, I will also check what my pump body temp is

[JAG1]

I like the return 'T'ed into the fill neck on both my 01 and 02. When I pour in 2 stroke for lubricity it also helps mix when running.

Edited May 29, 2021 by JAG1

[LorenS]

Silly question perhaps, but does dumping the fuel right into the filler neck significantly aerate the fuel? I don't have the deaerating style of pump. I know it gets aerated when I get fuel, but eventually the vast majority should leave.

 

I have planned on doing either a remote draw straw, or a remote fuel return. Since I have bad 1/4 tank issues (6 gallons or more in tank!) I may go the Mopar1973Man route with remote draw.

[Tractorman]

1 hour ago, LorenS said:

Silly question perhaps, but does dumping the fuel right into the filler neck significantly aerate the fuel?

 

Actually, it is a good question.  I really don't think it is an issue.  Larger air bubbles would stay at the surface and smaller bubbles would have time to rise to the surface before reaching the suction area.  I am sure that fuel sloshing around in the fuel tank while driving down the road generates a certain amount of aeration anyway - probably more than a return line to the filler neck would.  Just my opinion, but I think the gains from routing the return line to the filler neck greatly outweigh the risk of problems associated with aeration.

 

- John

[JAG1]

I can see mine flowing and the flow is a very smooth flow down the neck, not an agitated or one in which it might create much foam.

[Royal Squire]

Anyone know the ID of filler neck hose?

[Tractorman]

@Royal Squire, I don't know the specific size, but the filler neck tee that was recommended to me by @wil440is 1 1/2"  and the tee is 1/2".  It worked fine on my truck.

 

- John

10 hours ago, wil440 said:

As I have everything made to put my return into the neck I'll get on it and get it done and see what happens to my temps but as I said my fuel temps are low, highest I ever saw was 118F last summer towing my 5th back from Cumbria (North West England right on the Scottish border) 300 miles or so and that was 20 mile from home through a hilly built up area (City

 

It seems to me that you return fuel flow must not be entering the fuel basket since your fuel temperatures are so low currently.  Is the sump a factory setup?  There may be no benefit to adding the filler hose tee in your situation if in fact your fuel is being returned in a location other than the fuel basket.

 

- John

[Royal Squire]

@Tractormanthank you. 

[wil440]

5 hours ago, Tractorman said:

@Royal Squire, I don't know the specific size, but the filler neck tee that was recommended to me by @wil440is 1 1/2"  and the tee is 1/2".  It worked fine on my truck.

 

- John

 

It seems to me that you return fuel flow must not be entering the fuel basket since your fuel temperatures are so low currently.  Is the sump a factory setup?  There may be no benefit to adding the filler hose tee in your situation if in fact your fuel is being returned in a location other than the fuel basket.

 

- John

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