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BOSCH VP44 INJECTION PUMP AND LIFT PUMP FAILURES EXPLAINED
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 who you talk to and who you think is being honest, you will most likely get only some of the information you need. I will endeavor here fill in the gaps and get you up to date and informed; the reason I can tell you more is because Bosch had not, until 2004, allowed any franchised dealer to do anything except to send defective pumps back to the remanufacturing facility. Long before that Blue Chip had dismantled many pumps to figure them out and diagnose what failed and what caused the failure. We do not pretend to be any where near as smart as Bosch, but since there was no experience or information or truth out there, we felt we had to get the best information we could any way possible. Probably the most informative source were the applications for the patents applicable to the VP44. It was this dismantling and learning process that allowed us to get a patent and a performance product to market first.
The most common MECHANICAL failure with the VP44 pump is the cause of the code 216. This is when weak lift pumps with low fuel pressure over a perioid of time rupture the diaphragm in the front of the injection pump and the timing piston then vibrates and wears the housing of the pump until fuel bypasses the piston and full advance can no longer be attained. When full advance can't be attained for more than 5 seconds the code 216 is set. This means your pump has lost a lot of its power and fuel mileage and needs to be replaced and upgraded.
The next most common MECHANICAL failure is that the rotor seizes in the distributor section of the pump. I should note here that all previous rotary style pumps have had this problem too, to varying degrees. The most common cause and most accepted reason for this failure on rotary pumps is lack of lubrication due to running out of fuel or the possible lower lubricity of the newer low sulphur fuels.
In the case of the VP44 it is more common for the rotor to seize in the distributor because the pressures are MUCH higher and therefore mechanical tolerances have to be much smaller. Add the fact that the rotor was not "deburred" enough or correctly during manufacture, and these failures can be easily explained. Under the higher working pressure in the VP44, the edge of the slot in the rotor deflects and interferes with the distributor. Sooner or later the result is a galling of the two parts and then binding and then seizure. The seizure causes the "Drive Plate" to break and the truck stops running, never to start again until the VP44 is replaced. There is less than a half a thousanth of an inch clearance between the two parts, so it doesn't take much to make the rotor interfere with the rotor. Pumps made recently (since about 2000) are experiencing fewer of these kinds of failures, it seems to me.
The other reason injection pumps fail is ELECTRCAL issues and failures. These are the problems that cause 99% of the drivability problems. The computer on the top of the VP44 is susceptible to heat and many many heat cycles. The components on the circuit board develop bad connections due to crystallized solder over time and the result is intermittent hard start, white smoke and drivability issues such as the common " Dead Pedal". Rarely can these issues be verified or diagnosed by codes set in the ECM.
A lot of people have heard about bad lift pumps and think they are the cause of VP44 drivability issues and therefore electrical failures; NOT SO! Starting with the early 98’s, not only were they weak pressure wise, but also had exposed terminals on the bottom that corrode off in salt environments. 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, for that problem anyway!
If the lift pump is not delivering fuel pressure the truck stays running because there is a gear pump in the front of the injection pump, which keeps the fuel flowing, albeit at a much lower pressure than desired, and hopefully maintains lubrication to the rotor. As long as there is return fuel flow from the injection pump there is lubrication to the rotor, so low fuel pressure and certainly less return fuel makes it much easier to starve the rotor for lubrication. The only accurate way to test a lift pump is to monitor pressure UNDER LOAD and if it is above 5 PSI, no performance is lost and the pump is OK. If pressure is less than this, a modest reduction in horsepower results. The usual scenerio is a customer puts a performance box on his truck and the lift pump can't produce enough fuel to make more horsepower, and the performance product gets the blame.This sympton is most always a "Buck" as opposed to a "Surge" under load.
Often people have mistakenly said that increased pressure from add-on performance devices causes the injection pump failures. This statement only indicates their lack of knowledge, because, unlike most pumps, the VP44 pump does not create more fuel delivery by increasing lift pump pressure. The VP44 creates more fuel delivery by holding the fuel bypass solenoid closed longer. Fuel delivery pressure is controlled by the “pop off pressure “ of the injector.
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 installing and 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 with the distributor 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 AND BEAT RUN, you have a 90% chance your pump will not fail for a mechanical reason and therefore last until electrical issues start to show.
Lastly the installation of bigger injectors; do they alleviate the high pressure or raise the pop off pressure and therefore cause many failures of 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! Aftermarket injectors that DO raise the pop off pressure do not appear to cause any problems. Bigger injectors do get more fuel into the combustion chamber sooner, therefore 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