Injection Pump Mods

First things first. Let's look at the injection pump mods you can do to improve actual output and capacity. The Bosch P-Pump is a pretty eccentric piece of equipment with a lot of little moving parts that need to be dialed in near perfect if you want it to work to the best of its abilities. Luckily, DDP has done extensive testing and work to put together a list of parts that will do that. While we did all these mods with the injection pump sitting on a bench, they can be done with the pump installed on the truck.

First the fuel plate and android housing adjustments. After removing the factory AFC housing you'll find the fuel plate held down with two screws. It's common for most owners to just slide the factory fuel plate fully forward to improve fueling in the injection pump. Actual performance gains from that will be marginal-10-30 hp at best. DDP has developed a replacement fuel plate with a completely redesigned profile to work in conjunction with aftermarket injectors and other fueling modifications that we'll get into later. The DDP plate profile is cut to decrease fueling at lower rpms, then get more aggressive as boost and rpms rise. The plate is cut back again to decrease fueling at wide-open throttle for EGT control. With today's injector technology pulling fuel out at low rpms, the DDP fuel plate will help control smoke and egts as well.

The 1994-98 12V Cummins came equipped with a few different pumps, the best of which was the 215 hp pump. Our truck is an early 1998 model with an automatic transmission and came with a 180 hp p-pump. On these smaller 180 hp pumps swapping out the OEM Rack Travel Plug found on the front of the pump with one of DDP's deeper plugs can improve actual rack travel from a stock 18 millimeters to more than 21 millimeters. While that increase of 3 mm may not sound like much, Reed said the installation of the deeper Rack Travel Plug can make a noticeable difference in performance.

The next modification we made to our p-pump was with the factory governor springs. These are found under a plug on the side of the injection pump hiding under the throttle linkage. Note: be careful not to lose the small half moon woodruff key found on the post the linkage attaches to. When the plug is removed you'll be able to turn the motor over manually by the crank until you'll see the springs. There will be two sets of springs in the pump. Both need to be swapped out. Replacing the factory springs with the DDP aftermarket parts allows the pump to continue fueling heavy at higher rpms. That means power won't fall off as soon.