Engine/Transmission (1998.5 - 2002) Confussed on "how the low pressure side of the VP44" works.

[rweis]

I have been reading the TDR threads for a couple of years.



I have drawn conclusions that:



The lp fuel input goes to the internal VP44 vane pump that raises the pressure for input to the high pressure side of the VP44 that then raises the pressure to injection levels.



The excess lp pressure (over 14 psi that the overflow valve is set for) will be vented back to the tank and helps cool the VP internals.



THEN I bought "Diesel-Engine Management" by Robert Bosch GmbH 2005 4th edition (ISBN 0-8376-1353-1). Now I am REALLY confused.



Starting on pg 214 the Low-pressure stage.



The low pressure vane-type pump takes the output of the lp and raises it to 8-22 bar (116-362 psi) that feeds the high pressure side fo the VP44. It has a pressure-control valve that keeps the pressure from reaching too high a pressure during high pump speeds. However the vane-type pump generates 8 -22 bar (116 - 362 psi) that feeds the high pressure stage.



It also has a overflow valve that "In order to vent and, in particular, cool the distributor injection pump, excess fuel flows back to the fuel tank through the overflow valve screwed into the pump housing. Inside the valve body there is a spring-loaded ball valve which allows fuel to escape ehen the pressure exceeds the preset opening pressure. In the overflow channel to the ball valve, there is a bore that is connected to the pump overflow via a very small throttle bore. Since the overflow valve is mounted on top of the pump housing, the throttle bore facilitates automatic venting of the fuel-injection pump.



The entire low-pressure stage of the fuel injection pump is precisely coordinated to allow a defines quantity of fuel to escape through the overflow valve and return to the fuel tank.





What I do not understand:



In the diagram pages the overflow valve is AFTER the low pressure vane pump. Much we read on TDR says the pressure setting of the overflow valve is set to 14 psi. If the overflow valve is AFTER the low pressure vane pump aren't the pressures up in the 116 - 362 psi range? How can that be?



The diagrams of the fuel system in the VP44 do not show anything up in the low pressure vane pump end that would return fuel to the tank BEFORE it is pressurized.



Which also confuses how more than 14 psi from the lp wound do anything to help cool the VP44 IF the overflow valve is AFTER the low pressure vane pump's 116 - 362 psi.



Maybe the diagram in the book is wrong? 4th edition, doubtful



I will try to get a picture of the pump fuel diagrams.



Bob Weis



DOES anyone

 

[darkhorse]

I share your confusion, Bob. I'd like to see some good diagrams on how the "magic box" works.

 

[Texas Diesel]

Where did you buy that book?

 

[Bob Wagner]

Where did you buy that book?

http://www.bentleypublishers.com/product.htm?code=h011

 

[Bob Wagner]

http://www.bentleypublishers.com/product.htm?code=H144&subject=5

 

[Texas Diesel]

Interesting, does it cover the P7100 too? Common Rail? Obvioulsy it covers the VP in detail.

 

[rweis]

493 pages,





History of the dielse engine,

Areas of use for diesel engines,

Basic principles of the diesel engine,

Fuels,

Cylinder charge control systems,

Basics of diesel fuel injection,

Ovierview of fuel injection systems,

Fuel supply sytem to the low pressure stage,

Overview of inline fuel injection pump systems,

Presupply pumps for inline fuel injection pumps,

Type PE standard inline fuel injection systems,

Governors and control systems for inline fuel injection pumps,

Control sleeve inline fuel injection pumps,

Overview of distributor fuel injection pump systems,

Helix and port controlled distributor injection pumps,

Auxiliary control modules for distributor injection pumps,

Solenoid valve controlled distributor injection pumps,



sub components for this section

Areas of application

Designs

Fitting and drive systems

Design and method of operation

Low Pressure Stage

High Pressure Stage of the axial piston distributor injection pump

High Pressure Stage of the radial piston distributor injection pump

Delivery valves

High Pressure solinoid valve

Injection timing adjustment

Electronic control unit

Summary

and each section has many many sub components



Overview of discrete cylinder systems,

Single plunger fuel injection pumps PF,

Unit Injection System,

Unit Pump System,

Overview of common rail systems,

High pressure components of common rail systems,

Injection nozzles,

Nozzle holders,

High Pressure lines,

Start Assist systems,

Minimizing emissions inside the engine,

Exhaust gas treatment,

Electronic Diesel Control,

Electronic Control Unit,

Sensors,

Fault diagnostics,

Service Technology,

Exhaust gas emissions,

Emission control legislation,

Exhaust Gas Measureing Techniques



Are the sub chapters



It has flow diagrams, process sequence diagrams, component sequence diagrams, describes each in DETAIL.



However, is NOT consistant with what has been discussed a million times on TDR. Hence the confusion.



In the low pressure side of the VE / VP series the Outflow valve has nothing to do with the input 14 psi pressure. The outflow valve comes off the solenoid back side by the spring to cool the solenoid. It has zero to do with the 14 psi input pressure. However, for a long time here we have talked about supplying xx psi over 14 psi to the low pressure vane pump to help cool the Vp internals. Taint so, IF I AM READING THIS THING RIGHT, and hence the question.



Bob Weis

 

[NoSeeUm]

I would like to know also.



Has anyone ever tested the shutoff head pressure of the LP?

 

[Texas Diesel]

Which book do you have? Those two links are to different books.



I wonder if the 510 page one cantains all the info that the distributor manual does.



I would like to have one that covers both pumps but especially the VP.

 

[rweis]

I got mine from Bently Publishers and the ISBN is: ISBN 0-8376-1353-1 and is called "Diesel-Engine Management" Systems and COmponents by Robert Bosch GmbH 4th edition



Bob Weis



EDIT the first one Bob Wagner cited. The second one is supposed to be contained in the first one. There is a whole series (7?) of individual component books that the first one is supposed to encompass them all.

 

[Texas Diesel]

Book ordered!! Cant wait. I got the $60 one. Thanks

 

[rweis]

I am GLAD you ordered the book.



Solenoid control valve section starts on page 208.



I really need a couple of others to get the book and read through "our" sections. It sort of puts a different slant on how things work from what maybe might have become "gosspel" from what someone thought might happen years ago.



This is going to be REALLY interesting. I hope it clears the waters some so we can understand this thing (VP) better.



STICKS - where are you? We need someone who WORKS on these things to chime in.



Bob Weis



Plus when you read about the things they are going to do to diesels about EGR and UREA pumps etc back up in the last chapters, I have never been so glad I have an 02 without that stuff. The EGR controll systems look like "Rube Goldberg" at work.

 

[Bob Wagner]

the book price is money well spent for anyone. thanks robert

 

[NoSeeUm]

Read this: http://www.bluechipdiesel.com/injectionpumpfailures.html



A bit of a sales pitch included, but also some good info I think.



This is the part I found pertaining to your question to some extent.

If the lift pump fails the truck stays running because there is another vane pump in the front of the injection pump, which keeps the fuel flowing AND THEREFORE LUBRICATION to the rotor. As long as there is return fuel flow from the injection pump there is lubrication to the rotor. The existence of the vane pump in the front of the VP44 is why these trucks keep running with a bad lift pump! The only accurate way to test a lift pump is to monitor pressure UNDER LOAD and if it is above 5 PSI, no performance is lost and the pump is OK. If pressure is less than this, a drastic reduction in horsepower can be felt, especially when pulling a trailer. The usual scenerio is a customer puts a performance box on his truck and the lift pump can't produce enough fuel to make more horsepower, and the performance product gets the blame.



Often people have said that increased pressure from add-on devices cause the failure. This statement only indicates their lack of knowledge, because, unlike most pumps, the VP44 pump does not create more fuel delivery by increasing pressure. The VP44 creates more fuel delivery by holding the fuel bypass solenoid closed longer. Fuel delivery pressure is controlled by the “pop off pressure “ of the injector.

This explanation cleared up alot of things in my mind. I can only assume the vane pump also has some re-circ for cooling and lubrication purposes. As well as the LP itself.



In another article I have read, I just can't re-find the link, it said that during times of vehicle coasting the VP delivers zero fuel to the cylinders. What is bad about that is that the distrubution rotor is also not recieving any fuel. Unfortunately, fuel is also what lubricates it. That along with some small manufacturing defects and the very close metal to metal clearances leads to many VP failures as a result of the distrubution rotor seizing up. As also explained in the Blue Chip article.



More reading:http://dodgeram.org/tech/dsl/ISB/Vp44.htm and http://dodgeram.org/tech/dsl/ISB/vp44_reliability.html

In addition to the engine position reference pulse, the fuel pump control module (FPCM) also receives timing and fueling commands from the ECM. The fuel pump control module (FPCM) controls the timing and fueling through two solenoids located in the pump. The timing solenoid controls the position of a cam ring inside the pump by varying internal transfer pump pressure. The cam ring has evenly spaced lobes around its inner diameter. The pumping plungers ride on rollers that rotate inside this cam ring. The rollers follow the inner diameter of the cam ring and push the pumping plungers inward whenever a cam lobe is encountered, thus building injection pressure. By rotating the cam ring with the timing solenoid, the fuel pump control module (FPCM) is able to advance and retard the injection timing by making the rollers contact the cam lobes either earlier or later.



The second solenoid in the pump is used to meter fuel to the injectors. The solenoid opens the fuel metering valve to allow fuel from the supply pump to flow into the pumping chamber. Once the pumping chamber is charged with fuel, the solenoid valve closes. This traps the fuel in the chamber and allows injection pressure to build. The fuel is routed to the correct injector by the pump distributor. The distribution port on the distributor aligns with one of the six outlet ports to distribute fuel to a given injector. Once the desired amount of fuel has been injected, the solenoid valve opens, causing the pressure in the pumping chamber to bleed down, which ends injection. The cycle then begins again for the next cylinder

Timing in the VP44 is controlled by an internal timing piston coupled to a cam ring inside the pump. The timing piston is moved by fuel pressure. The amount of fuel pressure in the timing piston assembly housing is controlled by an internal transfer pump and a pulsating timing solenoid valve. As the pump speed increases, the fuel pressure to the timing piston assembly also increases.

Based on the inputs from the fuel pump control module (FPCM), the timing solenoid valve pulses to vary the pressure to move the timing piston, which results in the cam ring moving to the desired position to achieve the commanded timing. The more pressure created by the internal transfer pump and timing solenoid valve, the more the timing will advance; therefore, timing range capability is increased at higher rpms.

I think these parts will help you out as well. Differrent use of terms but I'm sure the "internal transfer pump " refers to the vane pump.



Jim

 

[MEastment]

In the low pressure side of the VE / VP series the Outflow valve has nothing to do with the input 14 psi pressure. The outflow valve comes off the solenoid back side by the spring to cool the solenoid. It has zero to do with the 14 psi input pressure. However, for a long time here we have talked about supplying xx psi over 14 psi to the low pressure vane pump to help cool the Vp internals. Taint so, IF I AM READING THIS THING RIGHT, and hence the question.



Bob Weis[/QUOTE]



Thanks for posting this information. I think I'm going to have to order this book as well. My question is does the book say anything about what pressure and flowrate should be delivered to the VP pump? One reply here suggests 5PSI under load - but what flowrate is that? I imagine that this varies with performance enhancements but if we knew what minimum and maximum flowrate/pressures a stock setup is supposed to supply to the VP then it might be possible to sort out what lift pump would be appropriate for different applications...

 

[NoSeeUm]

Thanks for posting this information. I think I'm going to have to order this book as well. My question is does the book say anything about what pressure and flowrate should be delivered to the VP pump? One reply here suggests 5PSI under load - but what flowrate is that? I imagine that this varies with performance enhancements but if we knew what minimum and maximum flowrate/pressures a stock setup is supposed to supply to the VP then it might be possible to sort out what lift pump would be appropriate for different applications...

Mark,



From another thread: https://www.turbodieselregister.com/forums/showthread.php?t=145413&page=1&pp=15

Jim: We do know the requirements of the VP44, 15GPH burned and 30GPH returned to the tank for a total of 45GPH at max.

I assume steved means 45gph at WOT for a stock 235Hp engine.



Jim

 

[MEastment]

Mark,



From another thread: https://www.turbodieselregister.com/forums/showthread.php?t=145413&page=1&pp=15







I assume steved means 45gph at WOT for a stock 235Hp engine.



Jim

Thanks!



Mark

 

[rweis]

Well, got back from visiting relatives for new years. Flight home was delayed a couple of hours so I started reading about the P7100 series.



In the P7100 series remember the cam OEM lp produces about 2 bar (~30 psi)? I think the reason is basically the P7100 uses fuel to cool the pump (engine oil to lubricate the pump). In the charge cycle and the piston is at the bottom dead center there is a fuel flow not only charging the plunger barrel assembly but also a fuel throughput that also cools the pump. As I read it that is why the lp psi is higher on the P7100's and why there probably became a following that higher psi from the lp promoted cooling the injection pump. True for the P7100, not true for the VP44.



However, in the Vp44 series the Overflow valve has NOTHING to do with the lp feeding the VP vane-pump. The vane pump is a low pressure (116 - 362 psi based on engine speed) pump to charge the high pressure pump and help (hydraulically) run the timing advance / retard of the cam ring (the Vp44 has a HYDRAULICALLY assisted (by fuel) timing device because of the higher pressures generated by the radial-piston distributor injection pump have to be dealt with - and is discussed on pg 230 "Hydraulically assisted tining-device").



I think for the VP44 crowd the idea of higher lp psi feeding the VP vane pump for cooling was a carry over that does not apply to the Vp44. HOWEVER, there are a couple of threads on the VP44 that state that Bosch expects 14psi (in a fairly narrow range of +- 1 or 2 psi) to be the feed pressure to the VP44. Susposedly (if I remember it right) the 14psi came from Bosch. Also in the thread of "pumps, lines, and whatnot" I think Bill K came up with lp test pressure up to 50psi and determined that higher psi (over 14 psi I assume) only created more heat in the Vp44 rather than more fuel throughput. He also measured the total fuel throughput and found higher fuel throughput at higher rpm. Some with fuel burned, but a lot of it was tank return fuel. And that holds true with the overflow valve being the return of the unused high pressure pump cycle fuel not sent to the delivery valve (ie when the solenoid collapses the high pressure to end the injection cycle). Which also holds true the OEM lp has nothing to do with the cooling fuel other than the charge the VP vane pump in the first place.



That would make sense with the explanation (pg 214) of the low pressure side vane pump. Once the vane pump rotating chamber is fully charged by the lp that is it for the lp having an effect. The vane pump vanes have an integrated spring on their backside (as well as centrifugal force) to help hold the vane to the eccentric retaining ring. I would think if there were TOO much psi coming from the lp it MIGHT have some detrimental effect on charging the VP's vane pump. Also there MIGHT be unnecessary fluid turbulance in the vane pump charging? How much lp psi is too much? I do not know. Guys are running 20 psi to the VP vane pump with good success I think.



The concept of volume that DC is pushing these days I think might be for the same reasons as above. The object is to fully charge the vane pump (ie volume). I do not know what psi that takes, but I would see where volume plays a role, but psi to get the volume into the vane pump fuel inlet (within the milliseconds allowed) plays a role as well. Sooooooo, a reasonable psi with fairly larger lines to satisfy the volume would seem to be the right balance. It does not say HOW MUCH fuel charge is in each VP vane pump pump chamber, it only says "The purpose of the vane-type supply pump is to draw in a sufficient quantity of fuel and to generate the required internal pressure (pg 214)"



The part about delivery of ZERO fuel during coasting I think is not quite right because the overflow valve has a throttle bore in it before the valve ball that allows a small quantity of fuel to flow at all times, but it looks like a VERY VERY small quantity as the throttle bore is very tiny. I think the main reason for the throttle bore is "Since the overflow valve is mounted on top of the pump housing, the throttle bore facilitates automatic venting of the fuel-injection pump(pg 215)"



I would like to thank all who have chipped in, this is gaining us better knowledge on this VP44 we all try so hard to keep healthy.



Bob Weis

 

[NoSeeUm]

I really wonder if the 14 psi was some magically engineered number, optimized to be perfectly matched for the VP44. Or just a number where the cards fell by using a xxx LP that supplied sufficient volume requirements of the VP44 pumping 14 psi at the minimum flow requirements. So could have 14 psi just indicated a "healthy" system?



The reason that I think this is because the new in-tank pump, I have read, only developes 7 psi. Maybe, the pressure is not as critical as once thought.

 

[rweis]

I think you are right, as long as the vane pump input chamber gets totally filled, then it seals and starts the vane pump pressure rise to feed the high pressure side.



Once the input chamber gets filled, the OEM lp (or whatever you are using) is out of the picture.



I am running 17 psi to the vane pump input chamber right now, and will get that adjusted to 14 psi and see if that changes any of the temperature measurements I watch. Who knows, probably will make absolutely zero difference. I do run AN-6 lines everywhere and full flow fittings everywhere to minimize any fluid turbulance.



Bob Weis