High Pressure Fuel Pump
| ITEM | DESCRIPTION |
|---|---|
| 1 | Crankshaft |
| 2 | Auxiliary drive chain |
| 3 | Oil pump sprocket |
| 4 | Auxiliary shaft |
| 5 | Acoustic cover |
| 6 | High Pressure (HP) fuel pump - Front (1) |
| 7 | Tappet |
The two High Pressure (HP) fuel pumps are identical mechanically-driven pumps installed on the right side of the oil pan body, behind the generator. An O-ring seal seals each of the HP fuel pumps in the oil pan.
The front HP fuel pump is identified as No. 1 pump, the rear HP fuel pump is identified as No. 2 pump. 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 body and the carrier of the auxiliary shaft. The auxiliary shaft is driven by the crankshaft via the auxiliary drive chain at engine speed. The auxiliary shaft is timed to match the pump delivery strokes with crankshaft position. A tappet on the end each plunger is operated by a two lobe camshaft on the auxiliary shaft. A spring, installed on the outside of the plunger, provides that the plunger and the tappet remain in contact with the camshaft.
During the downward stroke of the pump piston, fuel is delivered to the cylinder at a pressure supplied by the fuel tank mounted Low Pressure (LP) fuel pump. On the upward stroke of the piston the fuel in the cylinder is compressed. If the pressure from the pump exceeds the pressure in the fuel rail the fuel is delivered into the fuel rail via the HP fuel line.
The delivery rate of the fuel pump is adjustable by means of a fuel metering valve which is controlled by the Powertrain Control Module (PCM) with a Pulse Width Modulation (PWM) signal.
The cylinder and low pressure fuel supply are connected via the fuel metering valve. If the fuel pressure in the fuel rail is sufficient, the PCM opens the metering valve during the compression stroke of the piston. The fuel is then directed from the cylinder back into the low pressure supply to decrease the pressure in the fuel rail. A check valve is located between the fuel rail and the HP fuel pump. This prevents pressure dropping in the fuel rail due to fuel metering valve operation. The delivered fuel quantity depends on the engine speed and the actuation of the fuel metering valve.