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P-pump Swapping The ISB 24-Valve Cummins

Written By, Mike McGlothlin


The ISB 24-Valve 5.9L Cummins, most notable for its presence in ’98.5-’02 model year Dodge Rams, is an electronically controlled workhorse that’s known for its abundance of low-rpm torque and good all-around drivability. However, this version of the 359 ci inline-six is also infamous for its use of the Bosch VP44, an injection pump that—in addition to its fueling and rpm limitations—is plagued by both mechanical and electronic failures. In recent years, the list of computer-related problems associated with the ISB 5.9L has grown to include ECM failure. So between the myriad of VP44 reliability issues, dying electronics, and performance shortcomings, many 24-valve owners have turned to mechanical injection for a conclusive fix.

By scrapping the VP44 and reverting back to the Bosch P7100—the inline injection pump (a.k.a. P-pump) employed on ’94-’98 12-valve engines—ISB 24-Valve 5.9L Cummins owners get the best of all worlds. They gain reliability in the form of a fully-mechanical injection pump, and in combining the fueling capabilities of the P7100 with the higher-flowing 24-valve cylinder head they acquire an engine package with exceptional performance potential. While performing a P-pump conversion on the ISB 24-Valve is no small undertaking, we’ll show you which parts you’ll need to pull it off, as well as how far into the engine you’ll have to go.

VP44 Vs. P7100

As you’d expect, other than the fact that both pumps are cam-driven and feed mechanical (pop-off style) fuel injectors, there aren’t a lot of similarities between the electronically controlled VP44 (left) and the mechanical P7100. The VP44 is of a rotary, distributor type design and utilizes three pumping plungers whereas the P7100 has six plungers, one dedicated to each injector. The P7100 is also lubricated by both diesel fuel and engine oil, while the VP44’s only means of lubrication (and cooling) comes from fuel. Even in death, these pumps differ, the biggest killer of the VP44 being its PSG (the computer married to the top of it) and the common killer of the P7100 typically being old age (think at least 400,000 miles).


Performance Benefits Of The P7100

When fuel quantity per time is the name of the game (i.e. a high volume of fuel delivered very quickly), mechanical injection—and specifically a P7100—can’t be beat. Thanks to its design, the coveted Bosch P-pump can deliver a higher volume of fuel to the engine than a VP44 can, and it also boasts a much quicker injection rate. The P7100’s one drawback is that its injection timing is fixed, whereas the computer-controlled VP44 can vary timing to suit the appropriate fueling requirement in any given operating situation. Further performance gains can be realized with the P7100 through various wrenching tweaks and simple bolt-in parts.


P-pump Parts—What You’ll Need

A slew of parts is required to pull off the P-pump, 24-valve Cummins swap, most of which can either be sourced from the scrap yard, by browsing online, or through the aftermarket. In addition to the P7100 (which there are multiple versions of), you’ll need a gear housing intended for a ’94-’98 12-valve engine to accommodate the pump. You’ll also have to secure a drive gear for the pump, a throttle linkage, timing plug, the fuel lines that span from the P7100 to the injector crossover tubes and an intake spacer plate to clear the injection lines (shown). And don’t forget to source the correct cam sensor adapter.


No Small Job

Contrary to what the novice might think, converting an ISB 24-valve 5.9L Cummins to P-pump power is a fairly extensive undertaking. First, you’ll have to gain access to the front of the engine (and specifically the front cover and gear housing). To do this on a 24-valve Cummins, it means you have to pull the camshaft. For maximum working space on a ’98.5-’02 Dodge Ram, the coolant must be drained and the radiator removed, along with the intercooler and overflow reservoir. Additional requirements call for vacuuming down the truck’s A/C system, unbolting the upper radiator core support, and pulling the engine fan and shroud.


Limited Valvetrain Disassembly

Because the camshaft has to be pulled, the primary goal under the valve cover is to gain access to the lifters. After the rocker arms, valve bridges, push tubes, factory injection lines, and the VP44 are out of the way, you’ll have plenty of working room on the driver side of the block. Here, the ECM and tappet cover will be unbolted. It’s worth noting that the OEM tappet cover gasket is notorious for corroding, cracking, and leaking oil with age, making this an opportune time to install a fresh gasket or upgrade to a billet, RTV-sealed tappet cover. Of course, with camshaft removal being part of the job, it’s also a good time to upgrade—namely for a cam that better complements the P7100’s higher rpm fueling capabilities.


Pulling The Cam

In order to remove (and install) the cam from the block on the ISB 24-valve Cummins, the lifters have to be raised and held in place. If they’re allowed to drop, you’ll be pulling the oil pan. Homemade lifter holders or wooden dowels are commonly used, along with the dowels being cable-tied in place within the push tube bores. Then to all but guarantee no lifters fall when the cam is removed, each pair is cable-tied together. During the camshaft’s extraction, special care should be taken to not scuff or damage any of the cam bearings. Once the cam is out, further peace of mind can be found by inserting a 1.5-inch diameter pipe (at least the same length as the camshaft) into the cam bore.


Installing The P-pump

For the install of the P-pump itself, you’ll need the aforementioned 12-valve (6BT) gear housing but also the OEM gear housing gasket. The gear housing is installed using the two alignment dowels present in the block. With the gear housing in place, the camshaft can be reinstalled and the correct crank-to-cam timing verified. From there, the camshaft sensor adapter can be installed in the gear housing, along with the P-pump support bracket that bolts to the block and the pump and drive gear. The final torque spec for the drive gear nut calls for 144 ft-lbs—and a helping hand to keep the crankshaft from rotating.


Retained Parts And Mandatory Modifications

Those looking to perform a P7100 swap on their 24-valve Cummins might be surprised to learn how many components are retained. This goes for the camshaft sensor (which has to be kept in the equation in order for a ’98.5-’02 Ram’s tachometer to function), the front cover (although replacing the crank seal is highly recommended), and the ECM (more on that later). Then there are modifications that must be made in order to accommodate the P-pump. First, an external oil supply line has to be plumbed in, specifically for the pump. Unlike the VP44, the P7100 requires engine oil (which lubricates its governor springs and weights). As for mechanically controlling the pump’s fueling, a throttle linkage which incorporates the 24-valve’s accelerator position pedal sensor (APPS) will have to be made or purchased.


The 24-Valve ECM Remains

Another item of retention during a P-pump swap is the engine control module (ECM). While it’s no longer required for throttle position, the 24-valve engine’s ECM has to be retained in order for the factory gauges within the cluster and various temperature and pressure gauges to function properly in a ’98.5-’02 Dodge Ram. However, the ECM can be relocated to virtually any spot under the hood. This means it can be mounted independently from the engine, where the constant vibrations produced by the rugged 5.9L Cummins will no longer directly contribute to the ECM’s demise. It’s important to note that with the ECM no longer communicating with the VP44, a permanent check engine light will be present on the dash. Many DIY’ers simply remove the bulb from the gauge cluster while others choose to live with it.


Comprehensive Conversion Kits

As you might’ve already concluded, tracking down a 12-valve gear housing, P7100 drive gear, throttle linkage, having injection lines made, and all the other miscellaneous odds and ends that play into a P-pump 24-valve Cummins conversion can be time-consuming. But not only that, sourcing parts individually can get expensive. If you want to cut your parts hunting down more than 95-percent, several comprehensive P-pump swap kits are available in the diesel aftermarket. Names like Scheid Diesel (whose kit is pictured), Power Driven Diesel, Industrial Injection, and Crazy Carl’s Turbos offer complete kits to make the process as straightforward as possible. These companies even offer spiced-up versions of the P7100— or the DIY parts you need to unlock your pump’s vast performance potential.



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