HP Fuel Pump Schematic
| ITEM | DESCRIPTION |
|---|---|
| 1 | Pressure Relief Valve (PRV) |
| 2 | To HP fuel line to fuel rail |
| 3 | Check valve |
| 4 | Pump plunger |
| 5 | Fuel input from Low Pressure (LP) fuel line |
| 6 | Damper chamber |
| 7 | Fuel metering valve |
In addition to the plunger, the HP fuel pump contains:
- A damper chamber
- A fuel metering valve
- A check valve
- A PRV.
The damper absorbs pressure pulses from the plunger when the fuel metering valve is open at the start of the delivery stroke.
The fuel metering valve regulates the output pressure from the HP fuel pump. The fuel metering valve is a normally open solenoid valve controlled by the ECM. During the inlet stroke of the plunger the fuel metering valve is de-energized, which allows LP fuel into the pumping chamber. The ECM energizes the fuel metering valve closed during the delivery stroke of the plunger, which forces the fuel in the pumping chamber through the check valve into the HP lines. By changing the closing point of the fuel metering valve, the ECM can determine the volume of fuel output during the delivery stroke, and also the pressure in the HP side of the system.
The check valve prevents the return of HP fuel to the pumping chamber during the inlet stroke of the plunger.
The PRV protects the HP side of the system from excessive pressure if there is a failure of the fuel metering valve. If the pump delivery pressure increases to 195 - 204 bar (2828 - 2959 lbf/in2 ), the PRV opens and returns fuel to the inlet side of the plunger.