Bosch P-Size Pump

The P-size injection pump, although not physically the largest unit manufactured by Robert Bosch, is the biggest pump that is used on high-speed heavy-duty type truck and industrial engine applications. Note that it contains a sheet-metal protection cover held in place by screws, mounted on top of the pump to keep dirt and debris away from the barrel flanges. It is this cover that will allow you to quickly identify the model P injection pump from other Bosch models. The model P pump uses a separate governor housing, bolted onto the end of the pump housing.

The P pump is similar in construction to the MW model pump, in that both pumps employ shims underneath the barrel flanges to adjust the individual plunger lift to port closure, which is commonly known as prestroke on Bosch pumps. Prestroke is when the upward-moving pump plunger moves from BDC to the point where it covers the inlet ports in the barrel. The start of fuel injection would begin shortly thereafter once the trapped fuel reaches a high enough pressure to open the delivery valve.

Current model P pumps are capable of very high injection pressures. For example, the P7100 model can produce 1050 bar (15,225 psi) on the pump side and 1250 bar (18,125 psi) on the nozzle side. The uprated P8500 model can produce 1150bar (16,675psi) on the pump side and 1350bar (19,575psi) on the nozzle side. Both pumps use a 12-mm-diameter plunger with a plunger lift of 12mm and 14mm, respectively.

In addition, both the model MW and P pumps use bolted barrel flanges on the top of the pump housing that can be rotated CW or CCW in order to alter the delivery rate of fuel from each pumping element. However, both adjustments should be performed only when the pump is mounted onto a fuel pump test stand where the necessary special tooling and equipment is readily available.