Engine/Transmission (1998.5 - 2002) Why the VP44 pump fails

[Boldt's Wagon]

From Blue Chip:



http://www.bluechipdiesel.com/Bosch-VP44.htm

 

[Gary - K7GLD]

A good read - but I seriously question THIS part:



"The VP44 pump stops delivering fuel, shuts off all fuel, on deceleration which none of their other units do. This starves the rotor and distributor for fuel and therefore lubrication. "



It was pretty well discussed, and agreed, based upon careful examination of the VP44 in a long TDR thread that fuel does NOT stop flowing in the VP44, AS LONG AS the computer continues to sense engine/pump rotation - which makes good sense, after all, WHY would a manufacturer PURPOSELY stop fuel flow NEEDED for pump lubrication in situations like coasting down a long hill with no accellerator applied? That would pretty much be SUICIDE for the pump in those situations...

 

[KatDiesel]

Heres the thread about this article with some information in it... ... ... ... .....



Previous Thread on this article

 

[Gary - K7GLD]

That's a good thread too - but not the one I was referring to... The one I'm thinking of was more detailed in regard to the "no fuel flow without throttle applied" - and had more direct info as to exactly HOW sensors detecting engine/pump rotation continued to promote enough fuel flow to keep the pump properly lubed...



JEEZE, to do otherwise, would be like shutting down the engines OIL pump when it is coasting!



SURELY, the Bosch/DC guys are smarter than THAT!



(welllllll... )

 

[Ncostello]

After reading all that I have (theres a lot out there too!), I too couldn't imagine someone designing a pump that starves its own self of the very life blood that keeps it lubricated... diesel!! The first thing that came to my mind was coasting down some long grades where I live when I definately wouldnt be on the throttle. Now if I understood previous posts correctly, all of the fuel is returned to the tank if the engine does not need it for combustion. Therefore it would make sense to me that fuel should be flowing to... and then out of the VP44 to go for a ride back to the tank. Or does this returning fuel bypass the pump altogether if the pump is not injecting anything to the engine cylinders? What makes the most sense to me is that whatever provides the VP44 with fuel fails, whether it be its own internal pumping mechanism, or the lift pump. I'm not too familiar with the 24V engines, but thats where Im at right now.



I really want to purchase a 24V truck too, but until I can settle this for myself, I'm holding out (and missing out!). Am I supposed to fear buying a 24V? What do you even look for when you get the thing home for the first time. I would hate to spent 25K and have to start wrenching as soon as I pull it into the garage looking for a problem that may not even exist. What happened to the trust and reliability in these diesels? Should one only trust the 12V machines? Help.

 

[Ramafid]

Ncostello,



I wouldn't worry about the VP44 too much. I think the overall percentage of failure is pretty low ( at least later ones). The real problem is the lift pump. I think the only real way to help cure this problem is relocating the lift pump or adding a pusher pump. I opted for relocation with a new revised pump and have had no problems in 25k miles. ( Knock on wood ). The engine itself seems every bit as reliable as the 12v. Join in on the fun!

 

[KatDiesel]

Originally posted by Gary - KJ6Q

That's a good thread too - but not the one I was referring to... The one I'm thinking of was more detailed in regard to the "no fuel flow without throttle applied" - and had more direct info as to exactly HOW sensors detecting engine/pump rotation continued to promote enough fuel flow to keep the pump properly lubed...

Ya I know... . sorry... was posting to the "orginal thread starter"... . heres the one you speak of I bet.



The thread your refering to is huge..... and its the Ultimate VP44 Thread I think is the title.

 

[icarus33]

I'm running an April build 98. 5, in which I may even have one of the vp44's that might have missed some deburring process that could be a problem for early pump fail. I'm knocking hard on wood as I type this, but running a modified ecm and ddiii's I've had zero problems with the fuel system in 85k miles, 70k miles with the mods.

I've replaced the lift pump only as a cheap precaution due to the info on the running pressures.



Like anything mechanical, there's the good, the bad, and the ugly.



ic

 

[McDowra]

Gary ,

You are right that article contains quite a few mistakes.

 

[DBoyd]

To elaborate a little more on this subject, I just got off the phone with a service man with Diesel Injection Service in Corpus Christi. He said the reason the pumps fail is that when the lift pump fails it causes a bubble of air between the LP and the IP. The IP also has a lift pump in it and when the bubble hits it it causes the pump timing to foul up and the internals to fail. He said Cummins recommended to Dodge not to put a LP in line since the VP44 already has a lift pump in it and the additional pump wasn't needed. It just needs a little prime of fuel at start up like the mechanical pumps provided.

I don't know how this jives with what you all have heard but I thought the theory was interesting.

 

[RobbyRam]

I can tell you why my VP44 failed. I ran out of fuel three times, and my lift pump went out twice. Period! No other reason!

Bob in Sacto

 

[Ncostello]

DBoyd... interesting. However Cummins uses the exact same lift pump and setup on non Dodge applications such as Ford F-750's. Ours at work suffered the same lift pump/VP44 failure that plagues Dodge ISB's. It would stand to reason if Cummins recommended Dodge against the in line lift pump... they wouldn't use it themselves.

 

[BillGotthelf]

There are many reasons the vp44's are failing. On stock trucks the lift pump failures are killing the vp44's. On highly moded trucks its the heat and super high fuel flow that kills them. It all boils down to this high heat and not enough lube kills them all.

 

[Hohn]

That's why I think the Max Flow kit from Wildcat is such a great mod.



This kit drastically increases the volume of fuel flow available to cool the pump.



Has anyone heard of a VP44 failure on a truck with the max-flow mod?



I think that HEAT, not *just* lubrication is an overlooked element.



jlh

 

[rweis]

Does anyone cool their fuel before it goes into the VP?



Bob Weis

 

[Guest]

"Why the VP44 pump fails"



Cause it sucks!

 

[Ncostello]

Cause it sucks!

Then why are you driving one???

 

[Guest]

Well, Ncostello, I drive it for the motor not the pump! I didnt ask for a crappy pump when I bought the motor! Cause I bought the truck for the motor not the truck, Put a Cummins in anything and I would have bought it.

 

[tractorface]

Interesting

I was talkin to a person at Cummins (that is all I want to say for his sake) That knows a thing or two about any problems a Cummins engine might have. When asked candidly about the VP44 he said "It is so so, not near as reliable as we would have hoped" I asked some other questions about it but was told he was not an expert but if I really wanted to he could put me in touch with a guy at Bosch that was an expert. I declined because I did not think much good could come of it and I want to keep any needed favors in hand. (guys with 53's and KDP issues need not wear out favors until absolutely needed).



In the Grand scheme of things it doesn't suck (unless yours failed) it's just SO SO.



6. 0's suck, Yugo's suck, Monica... ... ... well you get the picture!

 

[Gary - K7GLD]

That's why I think the Max Flow kit from Wildcat is such a great mod.



This kit drastically increases the volume of fuel flow available to cool the pump.



The issue of fuel flow THRU the VP-44 has been covered here MANY times - and it's pretty well been established that only a relatively FIXED volume of fuel will EVER flow thru the VP-44 REGARDLESS of any reasonably provided fuel pressure, size of fuel lines, or the glamor of fancy fittings.



Tests have demonstrated that a MAXIMUM of flow thru the VP-44 is about 45 GPH - and THAT can be sufficiently supplied by the STOCK fuel lines and lift pump - providing larger lines, fittings and high-priced fuel pumps gains NOTHING as far as flow thru the VP-44 is concerned! About all that is gained from costly pumps is (hopefully!) greater reliability, and a more constant PSI into the pump with added power mods.



The only known variation as to the RATIO of fuel consumed vs fuel bypassed in the VP-44 is due to what is actually needed to power the Cummins under varying loads - more fuel consumed for power = less fuel available to be bypassed back to the tank - but that same 45 GPH is STILL the max that will actually flow thru the VP-44...



It seems we tend to forget some of the older groundbreaking threads available on this board - here's one that should be required reading for anyone considering involved and expensive mods to "help" the VP-44:



https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=11672&highlight=pumps