Engine/Transmission (1998.5 - 2002) The Ultimate VP44 Q&A Thread

[Diesel Freak]

Originally posted by Mark_Kendrick





What are the pop-off pressures and fuel flow ratings??



If you pump less fuel it's easy to do it faster. I did some calculations... at 50psi boost and 17:1 CR there's 1100psi of pressure in the cylinder about the time injection happens. depending on timing before TDC this is greatly reduced, but it's some interesting figures.



and if each cylinder gets 30cc in a smaller engine and we get 50 or 70cc it would be a huge difference in hydrolic requirements.

Mark, you bring up an EXTREMELY important point... ... . the smaller engines can and do run at those higher RPM's, but since the CTD needs a much larger fuel volume to run those RPM's what do you think would happen to the VP44 at 4000 rpm?



What do you think the duty cycle for the little solenoid doohickey is at those RPM's to allow enough fuel volume to produce 500 HP at 4000 RPM? Wouldn't you think it would be close to meltdown of the coil windings? Do you think the VP44 can withstand the forces required to pump greater than 70cc/min (honestly I have no clue what the flow rate is) at a pressure greater than 23000 PSI for an extended period of time?



Only if the coil is superconducting and the pump is made of "Unknownanium".



just a couple of thoughts... and no "missinformation" this time!

 

[Mark_Kendrick]

I have no idea about the flow rate either. . it was a 'for instance'



Those are the questions I have.

 

[Marco]

VP Rating

In reality you can know what flow rate the VP in your truck has.

Driverside, front of the engine, the engine data label can be found.

It states the idle speed, advertised Hp, NOx, and the fuel flow rate per stroke @ advertised HP.



My 99 AT sez 92 cubic mm per stroke, the ETH is rated @ 102 or 107 cubic mm can't remember the exact number.



Don't believe it? Watch your label.....



MK, you say:

. I did some calculations... at 50psi boost and 17:1 CR there's 1100psi of pressure in the cylinder about the time injection happens. depending on timing before TDC this is greatly reduced, but it's some interesting figures.



How did you calculate that number? No I don't know how to calculate it, but it seems rather low to me.

The latest Mercedes engines are build for peak pressures of 2175 Psi... They are all aluminium engines...



As for the Rpm question. The VP in the smaller engines has two plungers, while the one in the Ram has three of them. More volume can be pumped.



Ok, just looked in a Bosch book. They say that the VP can run up to 2400 RPM. Remember the injection pump runs at half the engine RPM. So 4800 engine Rpm



Pics later.



Marco

 

[Mark_Kendrick]

marco,

(50+14. 7~75)*17= 1275. . injection happens before tdc.



That's still a lot more than the 130-200 psi in a gasser.



4800 rpm huh? Coool! now tell me what it takes to get the ecm to run that high!! I'd need 1 less shift in the 1/4!!!



email me if need be.

 

[Marco]

VP pics

Pic 1

 

[Marco]

Pics

Pic 2

 

[Marco]

Pic 3

 

[Marco]

pic4

 

[Marco]

Pic 5

 

[Marco]

Pic 6

 

[Marco]

Pic 7

 

[Marco]

Pic 8

 

[Marco]

Pic 9

 

[Marco]

Pics

Now what are you looking at?



Pic 1, is the hole pump assy except the vane pump and the pumps housing.



Pic 2, is the pump element , note the high pressure outlets.



Pic 3, Inside view of the distribution head. The small holes in the background are the ones that bring the high pressure fuel ( Pic 2) into comunication with the cylinders.



Pic 4, is the fuel valve solenoid with the fuel valve ( needle with spring) inserted into it.



Pic 5, pump element with the fuel valve ( needle) inserted.



Pic 6, Pump element with it's plungers inserted.



Pic 7, pump element inserted into the "donut"...



Pic 8, Main shaft with the timing piston



Pic 9, a mistake, same as Pic 2... .



Marco

 

[Mark_Kendrick]

Which parts generally fail? what are the weak links?



Is there anyone who can over come the 3450rpm redline?



Is the redline set in the ecm or the vp44? combinational?

 

[Marco]

I have a question too...

Pic 9, there are the two slot's. ( Red and Black pointers).

Both of them are in comunication with the high pressure part.



The VP uses the slot with the black pointer to inject the fuel.

What is the other slot for? The Bosch disc does not even mention the second slot... .



OK, let's see the rev limiters. To tell you the truth, I'm still not completly certain as to where the rev limiter is.



There are four different Governed speeds.

(Governed speed is a little more diesel specific. )

Idle without load 900 Rpm. Idle with load 800 Rpm.

High Idle without load 3600pm. High Idle with load 3200 Rpm.



Fact is,

the VP has no way to know if there is or is not a load on the engine. Only the ECM can do that. So that would mean that the speed governor is in the ECM.



Fact two.

After over a year that I'm working on the ECM I'm still not completly able to overcome the 3200 RPM limit.

Better, sometimes I get over it, but not all the times. I still have not completly understood as to why that happens...



Maybe the governed speeds without load are in the VP, the ones under load in the ECM???



The 'puter in the VP is a LSI ( large scale integration) chip. No DF it's not epoxyed, it can be opened, but the only way to program it is via serial ( not OBD ) .



Who has the algorithm to program it? Only Bosch, as far as I know none else has ever been able to get it...



Marco

 

[Mark_Kendrick]

I have a few other questions. It is my understanding that the vp44 on the auto, 5spd and HO are different

I am told that:

the etc's use a '027' pump and the HO use an '028'.



What are the differences?

supposedly the 028 is higher volume and pressure.



the auto & 5spd are same except for the controller. the controller for the auto has a more favorable controller because the fueling curve is wider.



Are these differences accurate?



Now what about the VR pumps??? how do they differ from the VP pumps????

 

[Mark_Kendrick]

I almost for got...



If the fueling curve is determined in the VP44 then does the ECM merely tell the VP44 what % of the allowable fuel in the curve it wants???



I'm not real clear on the specific roles of the FCM and ECM and the nature of the data passed between them.

 

[Marco]

Yeah drill me with questions... LOL



MK your questions are bringing us into the right direction!



The rules of the game are: The ECM is the master ( except maybe for the governed speeds) the FCM is the EXECUTOR.



The VP does what the ECM tells her. Fuel rate and timing are determined by the ECM. Period.



Obviously there's a limit to what the VP can do. Read, timing,and

fuel pulse duration. Other than that the ECM rules.



The difference between the two VP's used in the Ram's is in the plunger size. That means that the "028" has larger plungers than the "027". This means in other words that the 028 can deliver more fuel in a shorter time. That's needed for emissions. BTW, the part's in the pics are from a ETH's pump.



Now a question for you, where did you get the 028-027 numbers from. I've never seen( or noticed) such a number on the VP.



Dunno a dime about the VR pumps, other than what has been said on the TDR.



The software for the AT-Stick trucks is slightly different. Mostly the fuel curve, the timing curve, and some other minor stuff.

The broader power band comes from a different fuel curve.



The HO's are different from the others cuz they have certain"limiters" in the ECM that the other's do not have.

When the ECM defuels, no box can overcome that defuelling.



Look at it in this way. A Hi FI two stage amplifier. The power stage is always ready to raise the signal from the pre amlifier.

What happens if the pre amplifier does not feed any signal, or a very low signal, to the final stage?

Bye Bye to party is over... .



Marco

 

[SmokinRam]

I Love This Stuff...

Marco Old Buddy,



You always seem to have such a way with words...



Andy