VP44 Injection pump failures

Currently FRYBRID is working on the issues associated with conversions to SVO
of vehicles ftted with the VP44 injection pump. There are many converted without issue
but this conversion should be done with an understanding of the risks.


        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 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, until recently, allowed any franchised dealer to service, dismantle or deal with the problems except to send defective pumps back to the manufacturing factory. Blue Chip has 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 information and or truth out there, we felt we had to get the best information we could any way possible. It is this dismantling and learning process that allowed us to get a patent and a performance product to market.

       The most common MECHANICAL problem with the VP44 pump 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 potential problem, 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 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 rotor was not "deburred" enough or correctly during manufacture. Under the higher working high 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. 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 electrical issues and failures. The computer on the top of the VP44 is susceptible to heat and heat cycles. The components on the circuit board develop bad connections over time and the result is hard start, poor perfromance, white smoke and driveability issues. Often these issues can be verified by codes set in the ECM.

        A lot of people now know about bad lift pumps and think they are the cause of VP44 failures; NOT SO! Starting with the early 98s, 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 youre all set!

       If the lift pump fails the truck stays running because there is another vane pump in the front of the injection pump, which keeps the fuel flowing AND THEREFORE LUBRICATION to the rotor. As long as there is return fuel flow from the injection pump there is lubrication to the rotor.The existence of the vane pump in the front of the VP44 is why these trucks keep running with a bad lift pump! 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 drastic reduction in horsepower can be felt, especially when pulling a trailer. 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.

    Often people have said that increased pressure from add-on devices  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 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 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 90% chance your pump will last a reasonable length of time.  Adding a power enhancement device that hooks to the solenoid wire can give you peace of mind that you can depend on the pump.

    We at Blue Chip have invented a pump tester that hooks up to the same wires that we use for our performance products 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.Our tester does not forecast life expectancy of the injection pump.

     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!  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


From the research I have done so far and the techs I have spoken to it seems that the weak point of th VP44 Injection Pump, which history has shown is prone to failure, is a design flaw causing rapid failure if the inlet fuel pressure is not maintained above 5psi at all times (both wide open throttle and under load).

It therefore seems that as long as the pump was healthy to begin with, and a VO pump capable of maintaining 5psi at all times were installed, that this pump should be capable of being converted to SVO.

I believe the sensible continuation of this research would be to have a willing owner of a VP44 equipped vehicle, who is completely aware of the risks involved, install a SVO system with the specified spec lift pump AND a low fuel pressure alarm. The carefully monitor the systems performance and longevity. Such a study is about to be carried out by BioCoupe custom vegetable oil fuel conversions and the results will be posted here.


Fuel System Components - 24-valve Cummins Turbo Diesel engine.

1. Fuel Transfer (Lift) Pump
2. Fuel Return Line (to Fuel Tank)
3. Fuel Supply Line (Low Pressure, to Engine)
4. Fuel Heater
5. Water-in-Fuel (WIF) Sensor
6. Fuel FilterlWater Separator
7. IA T Sensor
8. Map (Boost) Sensor
9. Fuel Drain Manifold
10. CKP Sensor
11. CMP Sensor
12. Overflow Valve
13. Drain Valve
14. Fuel Pressure Test Potts
15. ECM
16. ECT Sensor
17. Fuel Injection Pump
18. Throttle Lever Bell Crank and Apps
19, High-Pressure Fuel Lines
20. Fuel Injectors
21. Fuel Heater Temperature Sensor (Thermostat)
22. Oil Pressure Sensor
23. Fuel Injector Connector
24. Drain Tube
25. Intake Manifold Air Heater/Elements


Further reading: