High Pressure (Hp) Fuel Pump
| ITEM | DESCRIPTION |
|---|---|
| 1 | Accoustic cover |
| 2 | Bolt (2 off) |
| 3 | High Pressure (HP) fuel pump |
| 4 | Exhaust camshaft lobe |
| 5 | Gasket |
| 6 | Fuel pump support housing |
| 7 | Bolt 3 (off) |
| 8 | Bolt |
The HP (high pressure) fuel pump is located at the rear of the engine and is driven off the exhaust camshaft. The pump is mounted on a fuel pump support housing and secured with 2 bolts. The fuel pump support housing is attached to the cylinder head, sealed with a gasket and secured with 5 bolts.
The extended end of the exhaust camshaft protrudes through a hole in the end of the cylinder head. A 3 lobe cam on the end of the camshaft locates inside the fuel pump support housing and drives a plunger attached to the piston of the fuel pump.
Because the high pressure fuel pump is driven off the engine exhaust camshaft by a 3 lobe cam, the piston of the pump cycles at 1.5 times the engine RPM. (Engine camshaft turns at one-half engine RPM multiplied by three for the number of lobes on the exhaust camshaft).
A shield is fitted to the fuel pump to protect it from damage and an acoustic cover is fitted over the pump to dampen pump operating noise.
High Pressure Fuel Pump
| ITEM | DESCRIPTION |
|---|---|
| 1 | Fuel metering valve connector |
| 2 | Fuel outlet - high pressure to fuel rail |
| 3 | Fuel inlet - low pressure |
| 4 | Pump plunger |
| 5 | Tappet |
| 6 | Exhaust camshaft |
| 7 | Fuel pump lobes |
The HP (high pressure) fuel pump is a single cylinder pump which meters the fuel pressure according to demand requirements for correct fuel injection. The delivery rate of the fuel pump is adjustable by means of a fuel metering valve which is controlled by the ECM.
The high-pressure pump is mechanically driven by the camshaft via a plunger. A tappet on the end each plunger is operated by a three-lobe cam on the camshaft. A spring installed on the outside of the plunger ensures the plunger and tappet remain in contact with the cam. 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 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 high pressure outlet and a pipe.
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 ECM opens the metering valve during the compression stroke of the piston, decaying the pressure and directing the fuel from the cylinder back into the low pressure supply. A non-return valve is located between the fuel rail and the high pressure pump to prevent 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.
High Pressure (HP) Fuel Pump Schematic
| ITEM | DESCRIPTION |
|---|---|
| 1 | Pressure Relief Valve (PRV) |
| 2 | To High Pressure (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 (pressure relief valve).
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 (high pressure) 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 (low pressure) 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 PSI), the PRV opens and returns fuel to the inlet side of the plunger.