Description

Fuel Charging and Controls

NOTE:
A = Hardwired









PRINCIPLES OF OPERATION
The ECM (engine control module) controls the output from the HP fuel pump to deliver the required volume of fuel at pressures up to 150 bar (2175 lbf/in2).
The ECM (engine control module) also uses the signal from the FRP (fuel rail pressure) sensor to calculate the time the fuel injectors need to be energized to deliver the correct mass of fuel to the combustion chambers.

HIGH PRESSURE FUEL SYSTEM COMPONENTS









HIGH PRESSURE (HP) FUEL PUMP









The 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









The 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 (engine control module).
The high-pressure pump is mechanically driven by the camshaft via a plunger. 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 (engine control module) 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.

HP Fuel Pump Schematic









In addition to the plunger, the HP fuel pump contains:
- A damper chamber
- A fuel metering valve
- A check valve
- A PRV.
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 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 fuel into the pumping chamber. The ECM (engine control module) 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 (engine control module) 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 lbf/in2), the PRV opens and returns fuel to the inlet side of the plunger.

FUEL INJECTORS









Four HP fuel injectors are used. Each injector is side mounted in a port in the cylinder head. The fuel injectors are a push fit in the fuel rails and the cylinder heads. On each fuel injector, a rubber O-ring and support disc seals the head of the fuel injector in the fuel rail. A Teflon combustion seal ring seals the nozzle of the fuel injector in the cylinder head. The fuel rail provides positive location of each injector.
The injectors have seven holes for precisely controlled injection into each cylinder. Each fuel injector contains a solenoid-operated needle valve, which opens when the solenoid winding is energized. While the needle valve is open, fuel is sprayed into the combustion chamber. The solenoid winding is connected to a power feed and a ground from the ECM (engine control module). The ECM (engine control module) meters the amount of fuel injected into the combustion chambers by adjusting the time that the solenoid winding is energized.
If a fuel injector fails, the engine will suffer from unstable idle speed, poor NVH (noise, vibration and harshness) and poor emissions performance. The engine MIL (malfunction indicator lamp) in the instrument cluster will also be illuminated.
Each injector uses a 12V supply from the ECM (engine control module). However, hardware in the ECM (engine control module) pulls the voltage up to a 65V peak for half a millisecond and then holds it at 12V for the remainder of the injection event.

FUEL RAIL AND FUEL RAIL PRESSURE SENSOR

Fuel Rail
The fuel rail is located on the LH (left-hand) side of the engine below the intake manifold. The rail is attached to the head with 5 bolts. The fuel rail also secures the 4 fuel injectors in position. An O ring seal on each injector locates in a bore in the rail. As the rail is tightened to the cylinder head the fuel injectors are retained between the rail and cylinder head.

Fuel Rail Pressure (FRP) Sensor
A FRP (fuel rail pressure) sensor is located at the rear end of the fuel rail. The sensor is screwed into a threaded port in the rail and sealed with a mating taper in the rail. The sensor is connected directly to the ECM (engine control module).
The FRP (fuel rail pressure) sensor is a metal thin film technology type sensor. Three wires connect the sensor to the ECM (engine control module). The ECM (engine control module) supplies a 5V reference voltage to the sensor. The pressure measurement is based on the expansion of a thin steel diaphragm which is sensed by the ECM (engine control module) on a return signal wire which is proportional to the fuel pressure in the fuel rail.
The signal from the FRP (fuel rail pressure) sensor is used by the ECM (engine control module) as part of its calculations for the HP pump fuel metering valve operation.