The best way to start this explanation is to quote an e-mail that was found on the Cummins website. "The Bosch VP44 has not been as reliable as we had hoped". Depending on whom you talk to and whom you think is being honest, you will get only some of the information you need. I will endeavor here to get you up to date and informed; the reason I can tell you more is because Bosch has not allowed any dealer yet to service, dismantle or deal with the problems except to send defective pumps back to the factory. This means we can and have dismantled many pumps to figure them out and diagnose what failed and what the cause is for the failure. We do not pretend to be any where near as smart as Bosch may be, but since there was no information and or truth out there, we felt we had to get the best information we could.
The most common problem with the pump is that the rotor seizes in the distributor section of the pump. I should note here that all rotary pumps have had this potential problem, to varying degrees; this is nothing new to the injection pump world. The most common cause and most accepted reason for this failure on rotary pumps in general, is lack of lubrication. This can be due to running out of fuel or the lower lubricity of the newer low sulphur fuels. I think this is a fairly common reason for the VP44 to seize and the reason is that the lift pump providing lubrication/fuel to the injection pump, is frequently unreliable also. They intermittently don’t create enough pressure to run the injection pump but the reason the truck stays running is that there is another fuel pump built into the injection pump, that keeps it going but at a reduced power. A lot of people now know about bad lift pumps; starting with the early 98’s not only were weak pressure wise, but also had exposed terminals on the bottom that corrode off in salt environments, leaving the truck on the side of the road because the wire fell off! The way to tell if you have a corrosion sensitive pump is to see if the electrical connection is a plug on a 6-inch pigtail coming from the bottom of the pump. If the plug is on the top cover of the pump you’re all set! The other reason I think injection pumps fail due to lubrication is many people say their truck stopped running on deceleration and not full throttle. 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.
What actually happens when the rotor seizes, and this is from a Bosch Factory Rep, the slot in the rotor interferes with the distributor because of an inferior deburring process. In layman’s terms "deburring" is eliminating sharp edges. As a sharp edge isn’t strong it deflects under the 4600-PSI inside the pump. The sharp edge deflects and interferes with the distributor; it galls and then seizes. The drive plate then breaks and only the input shaft of the pump rotates. Other people have said that increased pressure from add-on device 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 largely controlled by the "pop off pressure " of the injector. We have proven this with a transducer on the injection lines.
The reason any aftermarket device that hooks up to the solenoid wire is blamed for the failure is that the failure 99 times out of 100 (honest numbers here) the pump fails within 20 minutes of running with power enhancement. The reason this happens is because the fuel solenoid is held closed longer, therefore using more length of the slot in the rotor. The slot in the rotor overlaps a hole in the distributor to allow for different timing and amounts of fuel to be delivered to the injector and when the solenoid holds the bypass solenoid closed longer, then the high "pop off" pressure is still there when the middle of the slot overlaps the hole. The middle of the slot is the weakest area and therefore deflects, interferes and seizes. Pump failure with fuel enhancement devices is not CAUSED by the enhancement device, but PRECIPITATED by the device. WE think this is a "glass half full" scenario rather than a "glass half empty" one, because the potential, eventual failure can be determined within controllable parameters, namely on the test run at higher power, close to home or the local dealer. The other side of the coin is, honestly, if your truck is still running 20 minutes after the installation you have a 99% chance your pump will last forever. Adding a power enhancement device that hooks to the solenoid wire can give you peace of mind that you can depend on the pump. The worst case scenario here is that the replacement pump may not be any more dependable than the first one. I know of a dealer that had to put three pumps on a 2000 truck to get it delivered to the customer! The good news is that we are seeing less and less pump failures out there; we know there have been at least three changes to the pump and hopefully they are all for the better and they are getting more reliable.
We at Blue Chip have invented a pump tester that hooks up to the same wires on the pump and can tell you in a very short time whether or not there are actual fuel signals going to the solenoid and therefore determining if the pump is working correctly. The only exception to this is if fuse number 9, in the fusebox on the left side if the dash, is blown; in other words, to diagnose a pump failure verify that fuse number nine is not blown and hook up our tester. Crank the engine and if the LED blinks you have a good pump; there are other rare kinds of pump problems, but if our tester says the pump is OK, the engine should at least idle and run. This is much easier and much less time consuming than either the Cummins tester or the DRB3 tool at the Dodge dealer.
Lastly the installation of bigger injectors; do they alleviate the high pressure and therefore failures in the VP44? Absolutely NOT. They are a bigger hole so fuel volume is increased at the same pressure. Remember fuel pressure is controlled by "Pop off" pressure more than the size of the hole! Again we have proven this with a transducer on the injection line. Bigger injectors do get more fuel into the combustion chamber sooner, therefore effectively advancing the timing and giving the engine better throttle response.
Bigger injectors are worth it but not for the reason of saving the pump.
Thanks for reading, Chip Fisher, owner of Blue Chip Diesel Performance
Attention: TDR Forum Junkies 
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If there's a pipeline compressor station in your area that uses 2-cycle engines, you might be able to sweet-talk the operator to give you a gallon or so of this oil from his storage tank. 
What about situations when you descent long, steep hills? I came down Cabbage Hill into Pendleton Oregon today and barely touched the throttle for 6-7 miles. That is an eternity if the injection pump is fuel starved. I can't believe that there is no fuel present inside the pump lubricating it, even if none is being delivered to the injectors. Plus, with a working lift pump, fuel should constantly be circulating back out the overflow valve and providing SOME cooling/lubrication. During decelation and no injection output, the demand for cooling should be minimal, but as long as parts are moving inside, you' d definitely want it lubed with fuel. 
