Engine/Transmission (1998.5 - 2002) VP44 Second Injection Event

[NoSeeUm]

Here on TDR I have read that the VP44 is capable of a 2nd injection event. By this I mean 2 injections per power stroke. This 2nd event is what fueling boxes utilize.



I have not been able to find any more information about this anywhere else.



Anyone care to drop a link or resource?



TIA;

Jim

 

[Gary - K7GLD]

Marco made reference to that in his lengthy CaTCHER thread on this board - lotsa reading, but it's in there! :-laf

 

[Bob Wagner]

Marco made reference to that in his lengthy CaTCHER thread on this board - lotsa reading, but it's in there! :-laf

Thanks Gary :-laf

 

[NoSeeUm]

This it? Post #669

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What Marco means is that when you have a major fueling box on your truck that taps the pump wire, it detects when your ECM send a signal to the VP-44 to start injecting fuel and the fueling box then adds on to that signal making the injection event longer, giving more fuel and thus making more power.

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Nope that's not the way the "major" fuelling boxes work.

The boxes that tap the pump wire do add an SECOND injection stroke after the ECM's one.



It works like this:

The ECM sends it's signal to the VP. The VP executes that command and injects the requested fuel with the requested timing by the ECM. The box adds then ANOTHER injection stroke AFTER the "main" injection stroke from the ECM. That's possible because the VP's have been designed for TWO injection strokes by Bosch from the beginning. The major fuelling boxes do "activate" an function that's already there but has not been used by Cummins. That can be easily seen hooking up a scope to the pump wire...



Clear as mud?



From the above it's also clear that:

1) Those boxes add fuel with a retarted timing ( the second stroke takes place later )

2) The EGT's will raise to abnormal levels ( late timing and more fuel )

3) These boxes sqeeze out as much fuel as the VP has in the plungers...



The CaTCHER does NOT add that second injection thus it remains within the save limits of the VP.



Marco

Not sure how it could work the way Marco states, with seperate strokes.



But would it be something like:



The fuel solenoid closes after the signal from the ECM as per normal. Then the fueling box adds a signal and the fueling solenoid re-opens. This all occurs during the same injection stroke of the VP44.



This more correct?



Jim

 

[Gary - K7GLD]

YUP - that's the one...



As Marco points out, the VP-44 is MADE for use of that 2nd injection event, and it is apparently used in other vehicle applications where the VP series pumps are used - so WHY would "activating" it with an add-on box be particularly dangerous?



Other than potential discussion as to the ability to provide most beneficial injection timing with a second injection event, the secondary issue is, which is harder in the pump - *2 shorter* injection events with other boxes, or one ONE longer one with a Smarty? The VP-44 fuel solenoid is a relatively high current device - will 2 short impulses be better, or worse than a single long one?

 

[NoSeeUm]

Read my edits Gary.



Sorry, premature postings.....



Jim

 

[Gary - K7GLD]

Read my edits Gary.



Sorry, premature postings.....



Jim

Not sure how it could work the way Marco states, with separate strokes.



But would it be something like:



The fuel solenoid closes after the signal from the ECM as per normal. Then the fueling box adds a signal and the fueling solenoid re-opens. This all occurs during the same injection stroke of the VP44.



This more correct?



Jim

That's the way Marco seems to explain it - not sure about the timing issue, and for sure, ANY device that adds fuel, a Comp OR a Smarty, will increase EGTs, all else being equal - and it's pretty clear as to the *total* power potential of the Comp vs Smarty, timing or not...

 

[JoeBioDiesel]

I like Jim's explanation better. When the VP is used in other applications, like some versions of the VW TDI, the pilot injection even is handled by the injectors, and definitely not the pump. If you've ever seen a VP apart it doesn't seem mechanically possible to have two injection events/cylinder, unless the fuel pulse was split up by the injector. There may very well be two pulses of the fuel solenoid, but I don't see how there could be 2 strokes of pump/cylinder.

Joe

 

[Gary - K7GLD]

I like Jim's explanation better. When the VP is used in other applications, like some versions of the VW TDI, the pilot injection even is handled by the injectors, and definitely not the pump. If you've ever seen a VP apart it doesn't seem mechanically possible to have two injection events/cylinder, unless the fuel pulse was split up by the injector. There may very well be two pulses of the fuel solenoid, but I don't see how there could be 2 strokes of pump/cylinder.

Joe

The VP-44 plungers merely provide the basic increase of fuel PSI - it's then the job of the internal and external system computers to determine the precise injection timing and volume of fuel applied, and the fuel solenoid is the electrical/mechanical "valve" that then controls that resulting fuel flow to each individual injector - if the solenoid is open longer, more fuel flow, open a shorter period, less fuel flow - all within the limits of the volume capability of the fuel plungers.



Multiple injection events are totally controlled by fuel system electronics and then applied by the VP-44 fuel solenoid - NOT the injectors!



The injectors themselves are "dumb" passive devices, and other than responding to line PSI and and their own pop-off pressure setting, control NOTHING as far as injection events are concerned - apply enough PSI, they open, otherwise, they stay closed - all purely mechanical.



For all intents and purposes, in our trucks, the individual injectors function much like sparkplugs in a gasoline engine - those plugs provide only a gap for electricity from an external source to jump - and when the voltage "pressure" is great enough, the gap is jumped. The plugs - and our injectors provide NOTHING themselves to affect the timing or number of events per engine revolution - THAT is a function in the diesels that only came with the common rail systems on 3rd generation trucks, where rail PSI is relatively constant, and fuel injection volume and timing IS electronically controlled at the injectors, but NOT true in OUR 2nd generation trucks!



The key in this issue, is the ability of the various electronics to properly apply the 2 individual injection events the VP-44 is designed for and capable of, in an efficient manner - as well as the ability of the fuel solenoid and it's electronics controllers to survive at longer high current applications than it might have been designed for when power boxes or programming are added.

 

[JoeBioDiesel]

Hi Gary,

I hesitate to argue too forcefully about the VP-44 because there are only a few thing that I know to be fact. The rest is an educated guess. Here is why I think what I do.

I know, for fact, that the VW TDI injector is what provides the pilot injection charge. It is done mechanically through the needle and springs, but the injectors definitely do that. There is no electronic control involved. Just mechanical parts. Of course we know that the Cummins does not have this type of injector... or they'd be much quieter.

I know, for fact, that the VP-44 is capable of some very fast fuel control. At full load, and at max RPM the fuel rack is capable of opening and closing the spill port fast enough to to deliver full throttle fueling to one cylinder and none to the next. Using most diagnostic scanners you can do a cylinder balance test at full throttle. The VP44 has one set of puming plungers(2), inside 1 rotor that do all the fuel delivery for the engine. That means the fuel solenoid can move the spill port from fully open to fully closed and back again between cylinder firings. That's fast!

Are you sure the solenoid you are talking about isn't the solenoid that controls the spill port? I don't believe it is mechanically possible to cap the plungers of a rotary pump without causing it to explode. I know that diesel fuel has some elasticity at injection pressures, but not that much!



It all would make sense if you're saying that at the end of a normal injection period the factory pcm commands the spill port open, stopping the injection event. The fueling box sees the injection event end and then closes the spill port again(allowing pressure to build in the injector line again) and causes a second injection event. I'd sure love to see that happen on ascope. Any chance anyone has some screen shots? or live close enough to me (near syracuse, NY)so I can get them myself? That'd certainly provide some answers quickly.

Joe

 

[Gary - K7GLD]

Hi Gary,

I hesitate to argue too forcefully about the VP-44 because there are only a few thing that I know to be fact. The rest is an educated guess. Here is why I think what I do.

I know, for fact, that the VW TDI injector is what provides the pilot injection charge. It is done mechanically through the needle and springs, but the injectors definitely do that. There is no electronic control involved. Just mechanical parts. Of course we know that the Cummins does not have this type of injector... or they'd be much quieter.

I know, for fact, that the VP-44 is capable of some very fast fuel control. At full load, and at max RPM the fuel rack is capable of opening and closing the spill port fast enough to to deliver full throttle fueling to one cylinder and none to the next. Using most diagnostic scanners you can do a cylinder balance test at full throttle. The VP44 has one set of puming plungers(2), inside 1 rotor that do all the fuel delivery for the engine. That means the fuel solenoid can move the spill port from fully open to fully closed and back again between cylinder firings. That's fast!

Are you sure the solenoid you are talking about isn't the solenoid that controls the spill port? I don't believe it is mechanically possible to cap the plungers of a rotary pump without causing it to explode. I know that diesel fuel has some elasticity at injection pressures, but not that much!



It all would make sense if you're saying that at the end of a normal injection period the factory pcm commands the spill port open, stopping the injection event. The fueling box sees the injection event end and then closes the spill port again(allowing pressure to build in the injector line again) and causes a second injection event. I'd sure love to see that happen on ascope. Any chance anyone has some screen shots? or live close enough to me (near syracuse, NY)so I can get them myself? That'd certainly provide some answers quickly.

Joe

Sorry Joe - you have MANY of your "facts" wrong!



There is NO fuel "rack" or "spill port" as such, in a VP-44 - and there are *3* fuel plungers, not 2!



Pretty much all the functions you ascribe to "Racks" and "spill ports" is what is handled in a VP-44 by electronics and the fuel solenoid - a FAR more sophisticated setup than earlier totally mechanical pumps!



It sounds like much of your assumptions and terminology are based upon the mechanics of a P7100 injection pump, and not a VP-44 - and as far as "capping off" the plungers and potentially creating an explosion in the vp44, that's what the VP-44 bypass valve and return line to the fuel tank is for, to bleed off excess fuel PSI and volume.



I'd suggest a bit more reading of the internals and functions of a VP-44 - I think you may be a bit confused between injection pump types - perfectly understandable, and no offense intended...

 

[JoeBioDiesel]

Hi Gary,

Actually I'm comparing it to the internals of a Roosa Master style rotaty pump. I've rebult 3 of them. 3 rotors? That a surprise to me. And no spill ports either? You're right. Time to get a book on the VP-44.

... and definitely no offense taken. I learn tons of stuff on these forums through discussions just like these.

Joe

Joe

 

[Gary - K7GLD]

Hi Gary,

Actually I'm comparing it to the internals of a Roosa Master style rotaty pump. I've rebult 3 of them. 3 rotors? That a surprise to me. And no spill ports either? You're right. Time to get a book on the VP-44.

... and definitely no offense taken. I learn tons of stuff on these forums through discussions just like these.

Joe

Joe

No, a SINGLE rotor, or "cam ring" as it's called (actually, the PLUNGERS "rotate" INSIDE the cam ring, and the cam ring is relatively stationary, other than relatively small rotation for fuel timing adjustment as engine demand changes), that actuates *3* plungers - yup, a little reading will help sort it all out - no problem!

 

[Partyat33]

My understanding is that the pulse from the ECM goes high, then a little lower, but not all the way down and the fueling box pulls that pulse back up.

 

[NoSeeUm]

Yeah, from my limited knowledge.



The VP44 has two solenoids controlled by a computor in the pump (FCM). One solenoid sets timing the other sets fueling. When the fueling solenoid opens it dumps (spills) fuel pressure off of the injector supply tube. The pop off needle valve in the injector only opens with sufficient pressure. So with the fueling solenoid open there is no pressure.



As far as the fuel injection pistons. They work contained with a distributor cylinder that rotates at 1/2 the engine speed much like a ignition distributor on a non fuel injected gas engige. Like the ignition distributor, there is a certain amount of plus or minus adjustability to adjust for timing changes over different RPM's. The pistons are contained within the distributor cylinder and are configured somewhat resembling the spokes of a wagon wheel. The direction of travel being from outer circumference to the center for the injection stroke (This correct?). From what I understand the pistons only make one direction of travel per injection cycle or one stroke.



With a 2nd injection event I am thinking that the fuel solenoid would open and close 2 times vice just one time for a single injection event all the while the injection piston is only making one stroke. That was my confusion from reading Marco's post.



I now think I understand more of what Marco was trying to say a little better. As I re-read what he typed a few more times it became easier to understand from his point of view. Which was I believe was more purely from the electronic viewpoint.



Seems like a 2nd injection event might be definately harder on injectors, but possibly easier on the fueling solenoid / VP44?



Jim

 

[Gary - K7GLD]

Seems like a 2nd injection event might be definately harder on injectors, but possibly easier on the fueling solenoid / VP44?

Dunno about that - but then, the injectors in the new common rail setups have 5 events per power stroke as I recall, with relatively few issues. But then, that's a different beast, so might not be a reliable comparison...

 

[GOT-Torque]

I think everyone would agree that the new common rail injectors are not more reliable than the 24V injectors...

 

[Gary - K7GLD]

I think everyone would agree that the new common rail injectors are not more reliable than the 24V injectors...

I may have gotten carried away - I was speaking in relation to the Ford and GM setups... :-laf

 

[georgej]

I was looking at a bosch manual on the vp44 and they show 2 plungers( or pistons),3 plunger and 4 plunger models. This together with various shaped cam rings and who knows how many events can be accomplished mechanically in a few nanoseconds

 

[Gary - K7GLD]

I was looking at a bosch manual on the vp44 and they show 2 plungers( or pistons),3 plunger and 4 plunger models. This together with various shaped cam rings and who knows how many events can be accomplished mechanically in a few nanoseconds

It appears that typically, the various VP series Bosch pump have half as many plungers as the engine has cylinders - 3 in our 6 cylinder Cummins, 2 in 4 cylinder installations, etc.



But it also appears from earlier claims by Marco, the the VP-44 in OUR setups IS capable of 2 injection events per firing stroke, and THAT happens under electronic control, not mechanical.