Bosch VP44 Injection Pump Cummins Application Disassembly and Reassembly

Disassembly and reassembly of a Bosch VP44 injection pump from a Cummins application. We show what the common parts look like and the common failures. The notes below dive deeper into the details of part failure causes and how to avoid them.

• If the PSG (pump mounted electronic control unit) to fuel control solenoid wires are damaged, we replace the PSG assembly
• A cracked diaphragm is caused by air in the fuel, or aerated fuel. Aerated fuel is caused by low or no engine supply pump, or lift pump pressure, plugged filter, running out of fuel etc.
• Housing advance bore damage and timing piston damage are also caused by aerated fuel. A sticky advance will not operate properly and is one cause for a P0216 code.
• Inside the pump, the pumping plungers deliver fuel by loading on the cam. The cam is moved by the timing piston, to advance the timing. If the fuel in the pump has air in it, every time the pumping plungers load on the cam, it compresses the air fuel mix behind the advance piston and causes the advance piston to slam toward the retarded side. While driving at 2000 rpm, then pump turns 1000 rpm, and the plungers load on the cam 6 times for every revolution. That means the timing piston slams retarded 6000 times per minute. It is amazing they last as long as they do with air in the fuel.
• Inside the pump, the supply pump pressurizes the fuel to operate the advance and feed the fuel control solenoid, which delivers fuel to the injectors. If the supply pump is worn, it can cause hard starting, particularly if the engine lift pump creates too much pressure (15 or more psi) at cranking.
• We check lift pump pressure with a gauge during WOT acceleration, instead of a volume test. The supply pump in the pump pulls fuel, and the lift pump on the engine pushes fuel. If the lift pump can't keep up, the pressure will drop. We consider 4 psi a minimum pressure and 8 psi to start watching the pressure. Aeration of the fuel is created by negative pressure, or cavitation.

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