Written By, Mike McGlothlin
The Bosch P7100 is one of the most coveted injection pumps in the diesel industry. Available in four-cylinder, six-cylinder and even eight-cylinder applications, it’s one of the most versatile and widely available inline plunger pumps ever manufactured. Better yet, its mechanical simplicity, million-mile durability, and penchant for unleashing additional horsepower have made it downright legendary, especially in ’94-’98 Dodge Ram 2500 and 3500s equipped with the 5.9L Cummins. Here, the P7100 (a.k.a. P-pump) enjoys celebrity status thanks to its ease of modification, near-infinite tunability, and Cummins-like dependability.
But there is some confusion surrounding the P7100s bolted to the B-series engines found in Dodge trucks. For starters, while most folks appreciate their unkillable nature, very few actually know what makes the P7100 tick. And then there is the fact that, across just five model years, four different power ratings (and three fairly different pumps) were used. To clear things up, this P7100 injection pump guide will show you how to properly identify your Ram’s P7100, explain how it operates, and also detail the key differences between each model. Your P-pump 101 tutorial begins here.
Different Pump Ratings For Different Model Year Rams
As a general rule of thumb, the horsepower (and torque) increases that came about during
the Cummins-powered Dodge Rams’ production run from 1994-1998, save for the 175hp version, coincided with changes in the P7100 that fueled them. The horsepower rating provided was also dependent on the type of transmission the truck was equipped with. For instance, the 160 hp version of the P7100 was offered in automatic transmission Rams for ’94 and ’95, while a 175hp pump was used in the manual transmission application for the same model years. From ’96-’98, automatic Rams came with the 180 hp P7100, while manual transmission trucks received the 215 hp unit.
Pump Codes Vary
Each P7100 is labeled with a three-digit code to identify its horsepower rating. For 160 hp
and 175 hp engines (’94-‘95), the most commonly found codes are 838, 841, and 854. Common codes associated with 180 hp engines (’96-‘98) include 885, 899, 911, 912, and 914. For the highly desirable 215 hp version (more on why that’s the case in a bit), typical codes include 887, 913, or 908. It’s worth noting that higher (as well as lower) hp ratings exist for the P7100, one common example being larger engines rated for 230 hp (think RV’s and school buses). Again, to keep things simple in this article we’re limiting things to the P7100 employed on the Cummins 6BT in ’94-’98 Dodge Rams.
How To Identify Which Pump You Have
Proper P7100 identification is important any time you’re repairing, rebuilding, or modifying the pump. The ID tag can be found on the driver side of the pump case, under the throttle linkage. In most cases, you’ll have to pull the linkage in order to make the ID plate completely visible. Throttle linkage removal calls for three 10mm bolts. Once visible, you simply run the numbers to find out which specific P-pump you have (keep reading to find out how to decipher what everything means). Do not obtain your numbers from the ID plate present on the back of the P7100. Those pertain to the pump’s governor spring assembly.
What The Numbers Mean
Complete identification of your P7100 can only be done by sorting through the assortment
of letters and numbers present on its ID tag. Starting with the PES6P120A120RS7369 shown here as an example, the “PES6P” represents the number of cylinders the pump serves (6), while the “120” that comes next denotes the barrel and plunger size in millimeters, less the 0 (i.e. 12mm). Next in line, the “R” in A120RS clarifies the direction of the camshaft’s rotation (and R means Right). The final four digits, which in this case are 7369, tell us the pump is of the 7000 series variety. Now, scrolling to the last set of numbers present on the second line, we find the pump code—and 887 means that this particular P7100 is one of the highly sought after 215 hp units.
Different Camshafts
As it rotates, the P7100’s camshaft lobes drive the pumping plungers up and down within
their respective barrels, creating the injection pressure required to fire the injectors. Across the four different horsepower ratings available on P-pump equipped ’94-’98 Rams, there were two different cams used. The 160 hp and 175 hp pumps both employ the 901 cam, while the 180 hp and 215 hp pumps use the 903 cam. Both cams boast 12mm of overall lift, but the 903 has a more advantageous return ramp—and it’s a return ramp that provides for a much quicker fill time, which ultimately leads to better performance at high rpm. The latter feature makes the 180 hp and 215 hp P7100s extremely popular in performance applications.
Different Delivery Valves
The delivery valves within the P7100 serve two purposes. One function is to isolate the high-pressure injection line from the pump’s plunger and barrel assembly (hence their placement between the plungers and their respective high-pressure fuel line). The second purpose is to decrease the pressure in the injection line and nozzle chamber in order to provide an abrupt closure of the injector nozzle. Ultimately, this makes for an efficient end-of-injection event, and prevents reverse flow from occurring. Delivery valves open based on the pressure present in the plunger cavity, and they’re forced closed thanks to the spring above them. Delivery valves known as 131’s are employed in the 160 hp and 175 hp P7100s. The 180 hp and 215 hp versions are equipped with 181’s.
Distinct Plungers and Barrels
Working their magic within the confines of their barrel, each pumping plunger in the
P7100 is responsible for creating injection pressure (which can exceed 15,000 psi). The plunger and barrel assemblies differ between the 160/175 hp pump, the 180 hp version, and the 215 hp unit, but all of them have the same diameter (12mm). Most notably, the 160 hp pump uses different length plungers than the 180 hp or 215 hp pump, the 180 hp P7100 utilizes flat-top plungers, and the 215 hp pump features a helix machined into the upper section of the plungers. This helix serves to alter injection timing and was implemented to help curb NOx emissions.
More On The 215hp Pump’s Upper Helix
To elaborate further on the upper helix present in the 215 hp P7100’s plungers, its function
is to retard injection timing, and it accomplishes this according to the range of rack travel. Once rack travel (the rack being what opens and allows fuel to enter the plungers and barrels) reaches a certain point, injection timing is pulled, which results in lower NOx emissions due to dropping combustion temperatures inside the engine’s cylinders. While this would seem to be a performance hindrance, your average pump guru can make the upper helix a non-issue when properly configuring the pump’s rack travel.
Flow Rates
Knowing the overall volume a P-pump can flow is front-page stuff in the world of diesel performance, but what’s really amazing is how conservatively a P7100 fuels in OEM form. As with their internal parts, flow rates vary from pump to pump—but all of them move very little fuel in factory, 6BT Cummins trim. For example, both the 160 hp and 175 hp P7100 flow roughly 135 to 140cc’s (the amount flowed per 1,000 strokes), while the 180 hp version moves 170cc’s. Not surprisingly, the performance-friendly 215 hp P7100 flows the most in stock form, at roughly 180cc’s. With modest modifications and the right Bosch P7100 injection pump parts for Cummins engines, any of these pumps can be tuned to deliver 300 to 400 cc’s of fuel.
Governor Assembly
The governor spring assembly is made up of a centrifugal weight and spring arrangement
that controls fueling within the P7100. The springs controlling the weights are used for high and low idle control, and these springs can be swapped out to provide more fueling at higher engine rpm. What are known as 3,000-rpm, 4,000-rpm, or 5,000-rpm governor spring kits are regularly installed in order to get the engine to continue to fuel beyond 2,500 rpm. An RQV is the standard governor type used on the P7100 found in Cummins-powered Dodge Rams, and while there are vague differences between the 160/175 hp, 180 hp and 215 hp units, the latter pump having left the Bosch factory with the lightest governor assembly.
