The dead pedal, the long-crank hot restarts, the engine dying suddenly while driving down the road, never to restart again. Yep, sounds like a ’98.5-’02 5.9L Cummins. This version of Cummins’ 359 ci inline-six, the 24-valve ISB, came equipped with the Bosch VP44 injection pump—an electronic rotary pump that is notorious for failing unexpectedly. It followed a period of time where the fully-mechanical Bosch P7100 aboard the 12-valve 5.9L offered in ’94-’98 Dodge Ram 2500 and 3500s wouldn’t die even if you were trying to kill it. Needless to say, the VP44 got a bad wrap from the get-go, effectively becoming the red-headed stepchild of the injection pump world.
But despite the VP44’s unpredictable nature and the fact that many prospective Cummins owners avoid them like the plague, it still enjoys a loyal following. With knowledgeable diesel mechanics, injection system experts and enthusiasts in that following, all of the VP44’s weaknesses have been exposed, well-documented and some have even fixed by the manufacturer over the years. To be sure, the VP44 remains one of the ficklest components to ever grace the legendary Cummins lineage, but there is now an unofficial protocol to follow in order to keep one alive. Below, we’ll highlight the key causes of VP44 failure and what can be done to prevent it from happening.
For more light reading on diagnosis and functionality of the VP44 from a highly reputable source, visit Blue Chip Diesel. It’s a company that has specialized in the ’98.5-’02 VP44 Cummins since it was introduced.
The Bosch VP44
To meet ever-tightening emissions standards on pickup trucks, Cummins introduced both a 24-valve cylinder head and electronically variable injection timing midway through Dodge’s ’98 model year. The ’98.5 5.9L ISB Cummins was equipped with the Bosch VP44 distributor style rotary injection pump. A cam-driven, radial piston pump, it features three internal pumping plungers, a fuel metering solenoid, a timing advance solenoid and a built-in computer called a PSG (or EDC) that monitors and controls fueling. The VP44 is capable of supporting 1600 bar (23,200 psi).
Most Common Failure
The majority of VP44 failures can be traced back to the PSG, the computer that’s married to the top of the pump. Excessive heat and thousands of heat cycles take their toll on the lead-free soldering that was used in the PSG’s internal circuit board, periodically interrupting the electrical signal. During PSG failure, several different symptoms surface, with the most frequent being long cranking when attempting to restart a hot engine. In recent years, better soldering has become part of the remanufacturing process on VP44s, which has led to improved reliability.
Rotor Seizure
Rotor seizure in the distributor portion of the VP44 is another issue that was especially common on early pumps due to an inferior de-burring process from the manufacturer. In essence, the sharp edge of the rotor makes contact with the distributor, digging into both mating surfaces. After enough contact (and damage), the rotor seizes up, breaking the drive plate. At that point only the VP44’s input shaft is left turning, but pressurized fuel is no longer making it out to the injectors. This sudden failure will stop your truck dead in its tracks.
Diaphragm Failure
The diaphragm, which is located at the pump’s distributor head inlet and supplies fuel to the bores of the distributor shaft, is also notorious for failure in early VP44s. Thanks to being made from a material that wasn’t up to the task of dealing with high-pressure fuel spill pulses, it was prone to cracking over time. The diaphragm’s life is further shortened when it’s exposed to lengthy periods with little or no fuel supply pressure from the lift pump. A hard cold start is the biggest indicator of diaphragm failure. The revised, later model VP44s came with a solid steel backing behind the diaphragm, which eliminated the flexing that resulted in failures.
Worn Out Distributor
Various internal components in the VP44 tend to wear out over time, the rotor and distributor being a couple of them. The distributor’s job is to route fuel from the pressurized pumping chamber through delivery valves, toward the injectors. When the distributor section of the pump is on its way out, hot restart issues will be present, and many times rotor and distributor failure go hand-in-hand.
Lack of Fuel Supply
Being that the VP44 relies on adequate fuel supply pressure and volume in order to operate, lubricate and keep it cool, a failing lift pump can spell disaster. Unfortunately, lift pump failure runs rampant on ’98.5-’02 Dodges. A self-priming, electric Carter lift pump came standard on the 5.9L ISB Cummins in Rams, but due to its being mounted on the engine block it is constantly exposed to vibration, which does not aid longevity. The factory fix was to replace the lift pump with an in-tank unit, and while that helped it didn’t provide the kind of reliability most customers expected. Bottom line: If the VP44 is not seeing at least 5 psi of fuel supply from the lift pump, it will not be happy.
Heat Is a Major Killer
A lack of fuel supply leads to hotter fuel being sent through the VP44—and as we’ve already alluded to, the VP44 doesn’t like excessive heat. Did you know the hottest the VP44 gets is actually 15 to 20 minutes after the engine has been turned off? This is due to heat soak. So if you’re driving a truck that makes frequent short trips and is subjected to a lot of hot restarts, your VP44’s life expectancy can be cut in half. Nine times out of 10, having trouble restarting a warm engine means the VP44 is on its way out. The only way to ensure the VP44 stays as cool as possible is to feed it good supply pressure and volume.
12-15 PSI Is Ideal
To keep the notorious chain reaction event of a failed lift pump from starving (and then killing) the VP44, 5 psi of supply pressure is the minimum you should see during idle, driving and/or wide-open throttle. Whenever possible, 12 to 15 psi worth of fuel pressure should be your goal. In the image above, the fuel pressure gauge is illustrating the fact that an ’01 Dodge Ram 3500’s non-functioning factory lift pump is supplying zero positive pressure to the VP44. Hooking up a mechanical fuel pressure gauge to a ’98.5-’02 truck is one of the first steps in diagnosing VP44-related failures.
Install a Reputable Lift Pump
Aftermarket electric pumps from Fuelab, FASS and AirDog have proven more than capable of delivering adequate pressure (again, 12 to 15 psi) to the VP44 on a consistent basis. For performance applications, both companies also offer comprehensive tank-to-engine fuel systems, complete with a high-flow electric lift pump, added filtration and larger diameter fuel lines. With good fuel supply, there is no reason why a VP44 can’t go 150,000 miles, if not 200,000 or more. Just remember to run a fuel pressure gauge in case you ever have an issue with your lift pump.
Mechanical Aftermarket Lift Pump
Power Driven Diesel’s Predator lift pump for ’98.5-’02 Dodges is relatively new to the Cummins aftermarket, but it shows a lot of promise. First and foremost, the pump is belt-driven and fully-mechanical, which means the faster you spin the engine the more fuel it pumps. Second, it features an internal pressure regulator valve that’s set up to work with the factory overflow valve on the VP44, which eliminates any possible overpressure scenarios. Last but not least, its 400,000-mile design means it will likely outlive any truck it’s installed on.
Get a Fuel Pressure Gauge
To keep tabs on the health of your lift pump (even if you’ve installed an aftermarket one), do yourself a favor and install a fuel pressure gauge. Trust us, the sooner you notice your lift pump no longer keeping up, the more money you’ll save in the long run by not having to fork over $1,000 or more for a remanufactured VP44. Some aftermarket gauges even offer a low fuel pressure warning light that you can configure to come on at whichever pressure threshold you deem as being too low.