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|VP44 Injector Pump Reliability Issues|
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An article appearing in the March 2000 issue of Petersons 4Wheel & Off Road quoted Dr. Diesel saying that the VP44 injector pump used on 24 Valve ISB Dodge diesel trucks was unreliable compared to the 12 valve engine's P7100 injector pump.
Curious about the claim, Roger Blind and Bill Alsip both e-mailed Cummins for a response. Cummins made some interesting comparisons between the ISB trucks and the 12 valve trucks. This is what Cummins had to say: Subject: 35259 :: Injection Pump Life
The 24 valve ISB engine in the 98 ½ Dodge has a Bosch
VP44 electronic controlled fuel pump. The engine has an electronic control module
connected to the pump as well as various sensors on the engine, the driveline
and electronic throttle pedal. Service on the Dodge Ram has been enhanced since
the engine electronics can be accessed with either Chrysler DRBIII or Cummins
INSITE electronic tools. The electronic ECM is designed for the Dodge application
and other controls are not compatible and there are no interchangeable chips.
Operating parameters are established by the Chrysler DRBIII or Cummins INSITE
The Bosch VP44 electronic fuel pump has higher injection pressures, electronic controlled timing and fueling which allows precise, instantaneous control and provides greater responsiveness over the entire power range (extended from 2700 to 3200 rpm). This is a completely new engine design platform that combines electronic engine controls with high-pressure injection as well as high strength engine componentry. The 24 valve design with cylinder centered fuel injection improves combustion efficiency which results in better emissions, fuel economy and performance. The VP44 is a radial-piston pump with 3 pistons. The pistons are attached to the distributor rotor and the fuel pump shaft. The pistons ride inside a cam ring (think of a donut with a "bumpy" hole) so as the pump shaft rotates the piston carrier, the pistons are compressed towards the center, pressurizing the fuel. The pressurized fuel is then directed to the proper cylinder by the distributor rotor.
The cam ring can be rotated in a "retarded" or "advanced" direction; this is done using a solenoid valve, which modulates pressure to a fuel-pressurized piston beneath the cam ring. Also, the start and end of injection are controlled by a solenoid valve.
Although the VP44 has initially not been as reliable as we would have liked, we (and BOSCH) are confident that its reliability will improve. The VP44 is much less complicated internally than the P7100, and it has many fewer finely machined parts.
We don't know for sure that BOSCH considered low-sulfur fuel when designing the pump, since the pump is fuel lubricated and today's fuels are low-sulfur.
The VP44 is completely fuel lubricated, as the VE pump is. It does not use oil lubrication like the P7100 does. The VP44 is expected to last at least a long as the P7100 in normal automotive applications. However, we obviously have much more "long-term" experience with the P7100 than we do with the VP44, so our knowledge base is still evolving. Soon after launch, the VP44 had its share of problems, just as the P7100 did when it was introduced, but we have worked closely with BOSCH to correct the issues with the pump, and we're confident that the VP44 will be a reliable fuel pump.
There are some significant differences between older trucks/engines and the newer trucks with the 24-valve engine. A Dodge pickup today can be 75 HP more powerful and almost 2000 lbs heavier than a 1991 W250; the weight of the trucks has increased yearly as Dodge has added safety and convenience features.
Also, the electronic controls on the 24-valve engine allow Cummins to control the power and torque very precisely across the entire RPM range. The mechanically controlled engines have their power and torque precisely controlled at torque peak and rated power RPMs, but between those two engine speeds, power and torque can often exceed the published figures.
Dodge set specific power and torque limits at particular RPMs for our engine, and with the electronic controls, we were able to meet them very accurately. This means that a mechanically controlled engine may produce more power and torque than a 24-valve engine at particular engine RPMs. This is most noticeable when one compares the trucks back-to-back, as someone who trades in an older Cummins powered Dodge would do.
While the 24-valve engine itself is more efficient than the older mechanical engines, actual observed fuel economy may differ between older and 24-valve trucks, due to the fact that
Thank you for choosing Cummins power or products.
Please let us know if you need assistance in locating the nearest Cummins-authorized
distributor or dealer. Please feel free to use our International Dealer Locator:
(http://www.cummins.com/partserv/intro.html) found on the Customer Assistance
page of the Cummins website (www.cummins.com).
Let us know if have other questions, or if away from your computer, feel free to call us (toll-free, from North America) at 1-800-DIESELS (343-7357), or 1-812-377-5000 (toll call, worldwide, ask for 800-DIESELS).
Powermaster Customer Assistance Center
Cummins Engine Company, Inc.
Columbus, Indiana, USA
My Comments (it's my web page and I get to add my $0.02 FWIW):
On one hand, several people have caught the Cummins
statement: We don't know for sure that BOSCH considered low-sulfur fuel when
designing the pump.
On the other hand, Cummins insists that the pump is designed for low sulfur fuel and no injector pump lubrication should be added to the fuel.
On the gripping hand*, there have been VP44 failures caused by insufficient fuel flow from weak fuel transfer pumps, many after only a few hours of operation with low fuel feed pressure. To me, the failures indicate that the fuel lubrication is essential to the life of the VP44 and, if there is not sufficient flow or lubrication, pump life is short. Injector pumps on the 1998 and 1999 model years have have the most trouble.
On the TDR forum, there has been a raging debate about VP44 injector pump damage caused by restriction in the PrimeLock remote fuel filter system. The jury is still out, but it appears that the PrimeLock filter adapter DOES reduce fuel pressure readings from the lift pump to the injection pump. When a lift pump is marginal (there have been two bulletins released by Dodge about marginal and failing lift pumps), the added restriction from ANY accessory in the fuel line can cause injector pump failure. Be very careful about adding accessories that might cause failure of an expensive part, Dodge will probably attempt to deny warranty coverage. Here is the thread, but it has become somewhat inflammatory and may be deleted.
One thing you should know:
From the service manual "The VP44 is cooled by the fuel that flows through it. ... Approximately 70% of fuel entering the pump is returned to the tank through the overflow valve and fuel return line."
The VP44 does not inject fuel when the throttle is closed and the engine speed is above idle (i.e. decelerating or coasting). When no fuel is being injected, all of the fuel is returning to the tank and the injector pump's distributor rotor head is turning with no cooling or lubrication from fuel. I don't know how long the rotor can run with no fuel, but a lubricating fuel supplement will help maintain a film on the rotor head to help keep it cool. IMHO: Everyone with a VP44 pump should use a polymer based (not alcohol based) fuel additive that contains a pump lubricant. I use it in Sue's 2001 ETH because it doesn't cost much, and it may help keep these relatively fragile (and expensive) pumps functioning. Some suggestions: Standyne Performance Formula, Power Service Diesel Lube, and Marvel Mystery Oil. All have excellent reputations. Other folks are using Howes Lubricator Meaner Power Kleaner, Pro-Tec Diesel Fuel Conditioner, and Rotella DFA. DO NOT USE AUTOMATIC TRANSMISSION FLUID. Tranny fluid contains friction modifiers for the clutch packs, and these additives are not good for injection pumps. As always, YMMV! -Dave-
Last Update: December 2, 2001
* The gripping hand reference (three way logic) comes from
The Mote in Gods Eye, by Niven&Pournelle