High Pressure Fuel Pump
The High Pressure (HP) fuel pump is located on the top of the engine. The HP fuel pump is attached to the camshaft carrier with 2 bolts and sealed with an O-ring seal. A protective shield covers the HP fuel pump which is secured to the camshaft carrier with 4 bolts to protect the HP fuel pump from any damage.
The HP fuel pump is mechanically driven by the exhaust camshaft via a plunger. A tappet on the end of the plunger is operated by a 4 lobe cam on the exhaust 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 HP fuel pump piston, fuel is delivered to the cylinder at a pressure supplied by the Low Pressure (LP) fuel pump. On the upward stroke of the HP fuel pump piston, the fuel in the cylinder is compressed. If the pressure from the HP fuel pump exceeds the pressure in the fuel rail the fuel is delivered into the fuel rail via a single HP fuel pipe.
The delivery rate of the HP fuel pump is adjustable by means of a fuel metering valve. The fuel metering valve is controlled by the Powertrain Control Module (PCM) with a Pulse Width Modulation (PWM) signal.
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 the 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.