High Pressure Fuel Pump
The HP fuel pump is located on the top left of the engine. The HP fuel pump is attached to the camshaft carrier with 2 bolts and sealed with an O-ring seal.
The HP 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 PCM with a Pulse Width Modulated (PWM) signal.
The HP fuel pump is mechanically driven by the intake camshaft through a tappet. The tappet is operated by a 3 lobe cam on the intake camshaft. A spring installed on the outside of the plunger holds tight the plunger and the tappet remains 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 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 through a single HP fuel line.
The cylinder and low pressure fuel supply are connected through the fuel metering valve. If the fuel pressure in the fuel rail is sufficient, the PCM opens the fuel 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.