High Pressure Fuel Pumps
| ITEM | DESCRIPTION |
|---|---|
| 1 | Crankshaft |
| 2 | Auxiliary drive chain |
| 3 | Auxiliary camshaft |
| 4 | Tappet |
| 5 | Rear High Pressure (HP) fuel pump |
| 6 | Acoustic cover |
The High Pressure (HP) fuel pumps are identical mechanically-driven pumps installed on the right side of the oil pan, behind the generator. An O-ring seals each of the HP fuel pumps in the oil pan. The front HP fuel pump is identified as 1, the rear HP fuel pump is identified as 2. An acoustic cover is installed on each of the HP fuel pumps.
The HP fuel pumps are single-plunger pumps. The plunger of each pump extends through the oil pan and the carrier of the auxiliary camshaft. A tappet on the end of each plunger is operated by a 2 lobe cam on the auxiliary camshaft. A spring installed on the outside of the plunger makes sure that the plunger and tappet remain in contact with the cam.
The auxiliary camshaft is driven by the crankshaft, via the auxiliary drive chain, at engine speed. The auxiliary camshaft is timed to match the pump delivery strokes with crankshaft position.
High Pressure Fuel Pump Schematic
| ITEM | DESCRIPTION |
|---|---|
| 1 | Pressure Relief Valve (PRV) |
| 2 | To High Pressure (HP) fuel lines |
| 3 | Outlet check valve |
| 4 | Plunger |
| 5 | Supply connection from Low Pressure (LP) fuel lines |
| 6 | Damper chamber |
| 7 | Fuel metering valve |
In addition to the plunger, each High Pressure (HP) fuel pump contains:
- A damper chamber.
- A fuel metering valve.
- A check valve.
- A Pressure Relief Valve (PRV).
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 Powertrain Control Module (PCM). During the inlet stroke of the plunger the fuel metering valve is de-energized, which allows Low Pressure (LP) fuel into the pumping chamber. The PCM energizes the fuel metering valve closed during the delivery stroke. The delivery stroke 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 PCM can determine the volume of fuel output during the delivery stroke, and thus the pressure.
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 250 bar (3625 psi), the PRV opens and returns fuel to the inlet side of the plunger.