Engine/Transmission (1998.5 - 2002) VP44 Timing

[HoleshotHolset]

There's software in the little computer underneath the 'pump cover' on a VP-44. That computer is responsible for translating the CAN-BUS commands/parameters to and from the Cummins ECM bolted to the side of the block.



The solenoid valve is controlled by that little computer - with input values based on what the Cummins ECM suggests. That little valve is the single most important part of the pump to consider when trying to advance the timing electronically... it has mechanical limits and you have to remember that.



On edit: Since the solenoid valve has to open and close a minimum of one time per injection event (you have 6 injection events for every complete rotation of the pump... keeping in mind that the pump spins at 1/2 engine speed) - you can see that at 3500+engine rpm... it's a busy little beast. Eventually, when the mechanical limits of the solenoid is reached... it could fail... sorta like floating the valves.



You don't have to modify the Bosch software to get it to go past a certain RPM... you just have to fool the ECM and the little VP-44 computer into thinking that everything is within normal operational parameters. Non-OEM programming would reduce the amount of tom foolery involved and could allow more complete control over the whole process.



Matt

 

[Marco]

Quote HoleshotHolset,

That little valve is the single most important part of the pump to consider when trying to advance the timing electronically... it

The valve you're talking about is the fuel metering valve; how much fuel is injected. Has nothing to do with the timing of the VP.



The dynamic timing of the VP is done rotating the whole plunger assembly inside the distribution head. It has a limit of +/- 30° Crankshaft.



Aloha,

Ciao,



Marco

 

[MCummings]

Marco.



How much timing can you give us with your ECM?



I know Doug told me he tried a 20* timing program from you, but blew a headgasket.



What he told me was,,, Timing wasn't as big as a factor as he thought it would be.





Merrick

 

[HoleshotHolset]

Marco: Thanks for the clarification. You're right... the solenoid valve I was referring to is responsible for injection quantity, not the injection timing.



And now for some goodies (keep in mind that thes pictures are from a 4-cylinder version of the VP-44):

This is a good schematic showing an 'overview' of the parts that maintain timing: #ad




Here's an exploded view of the cam ring, timing device, and pulse valve - with an excellent explanation of the whole process: #ad




This is a very good shot of how the timing device moves the cam ring to advance/retard the timing. I marked the area that we're most interested in on the upper part of the 'Retard' side... This illustrates the mechanical limits of the timing device (which is controlled by the pulse valve) that controls the start of injection timing: #ad




After looking at these pics and reading Bosch's explanation - you can get a pretty good understanding of the timing section of the pump (and see how I wasn't exactly correct with my previous statements... ). If folks are interested in the low pressure, high pressure and distribution sections... I have pictures of that stuff as well. I can also take pictures of some of the actual VP-44 parts... but Bosch's pictures are way better than what I can do.



Matt

 

[csevers]

I think timing is very important depending on how much fuel you are putting in the cylinder and the engine rpm. I would like 30 btdc if possible and if I could adjust it with a dail or something that would be most awsome.



Craig

 

[Marco]

How much timing can you give us with your ECM?



Within the limits of the VP, anything...

Hey, I'm controlling the brain of the system!



Doug told me he tried a 20* timing program from you, but blew a headgasket.



Poor Doug! :-laf I told him it would've been too much timing. He wanted it, he got it, he payed for the damage... :-laf :-laf :-laf





I would like 30 btdc ... ... .



That statement is uhmmm... incomplete!?!

You have always to consider that the VP timing is dynamic, it's adjusted to various factors. Rpm, load, intake temp, engine temp...



So, 30° BTDC, WHEN???

Just as a side note 30° BTDC is too much.....



Marco

 

[MCummings]

How much timing can you give us with your ECM?



Within the limits of the VP, anything...

Hey, I'm controlling the brain of the system!



Doug told me he tried a 20* timing program from you, but blew a headgasket.



Poor Doug! :-laf I told him it would've been too much timing. He wanted it, he got it, he payed for the damage... :-laf :-laf :-laf





Marco

Marco,

I know it's possible, but when can you do it?



Give us a "Dial-a-time" for our 24V's



Some of us are nucking futs, and want to crank 30* at 3,800RPM @ 80PSI.



Can you give us a "Auto", "Fixed" and "Dial-a-time" setting?





Yah, Doug isn't afraid to test something. :-laf



Merrick

 

[csevers]

Yes 30 maybe to much for a 24v only turning 4k rpm. This is for sled pulling ONLY not for street use so I want ok maybe say 25 degrees at 2700 to 4000 rpm, engine temp at 140 plus, full throttle, full load and any intake temp. I don't need it to be "dynamic" just turn on, on the track run and turn it off at the end of the track. It doesn't have to be smooth and I am not to worried about my headgasket. If the timing could be controled by a variable dial type switch it could then be tuned to ambient temps and other changes from one event to another easily.



Asking to much??

Thanks for any input you have Marco

Craig

 

[GregFisher]

holeshot, great pics of advance unit for the vp 44, now if you can look at that picture it becomes obvious the total amount of possible advance. only possible solution for more advance is to change the lenght of the advance piston which would allow it to move a greater distance. however when we talk about advance we have to keep in mind what is occuring within the hyd. head. the rotor the part that spins inside the head has one discharge port and must be in allignment with the discharge port of the head ( which there are 6 of ) during the injection cycle to allow the pressurized fuel to travel to the injector. now if we move the advance piston to one extreme or the other and fuel is trying to be pressurized with these ports not in allignment a severe seizure will occure, because of fuel trying to be injected with no where to go. one thing you must remember with any injection pump even though an injector may have an opening pressure of 300 bar (4300 psi ) this only controls when beggining of injection occurs in the engine actual peak line pressure of the vp 44 is upwards of 1200bar 18,000 psi if the rotor is trying to distribute this fuel out of allignment with the discharge port of the head instant seizures will occure.



thanks, greg

 

[HoleshotHolset]

Greg,



You make some VERY valid and important points. Honestly, I don't think we have to even open up the VP-44 at all to get our 15° of pump timing. All we need to do is fool the ECU/ECM into thinking that 30° of engine timing is OK...



I don't think that Craig or any other VP-44 owner needs more than 30° - and the general consensus is that 30° is 'do-able' with the VP-44 as is.



If Craig gets his 30° and starts eating pumps or something else at least we know not to do that anymore.



Matt