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. The diaphragm has been updated to a more robust style, and we install the latest update in all pump rebuilds.
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. The housing and advance piston design have been improved, for better reliability and longer lasting. We use the latest version in our rebuilt injection pumps.
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 behind the cam 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 (supply pump) creates too much pressure (15 or more psi) at cranking.
We check lift pump pressure on the vehicle with a gauge during WOT acceleration, instead of a volume test. The supply pump in the injection 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.
VP44 Pump Calibration – Testing Notes
The PSG (pump controller) must be programmed with the Bosch programming on the Bosch EPS815 test stand. New PSG assemblies come blank, with no programming, from the factory.
The proper key is installed after calibration, based on the timing and tolerances internally in the pump. The offset in the key is for minute timing adjustments, and the arrow on the key goes toward the pump. We stamp the key number on the pump nameplate area, in case the key gets misplaced. It should only be replaced with the correct key, and when we install a key, we stake it to keep it from falling out of the keyway.
The loop on the top of the pump housing, near the mounting surface, is for timing verification – Do Not Pry on it.