1 Electromagnetically operated fuel metering valve
2 Piston
3 Bush
4 Compression spring
5 Coil
6 Armature
NOTE: During repair, the fuel metering valve must not be removed from the high pressure pump. The pump may only be replaced as a complete unit.
The fuel metering valve is bolted directly onto the high pressure pump.
Depending on the fuel pressure in the fuel rail, the fuel metering valve regulates the fuel feed (and consequently the fuel quantity) from the transfer pump to the high pressure pump elements.
This permits the fuel quantity supplied to the high pressure pump to be adapted to the engine requirements from the low-pressure side. This minimizes the fuel quantity that flows back to the fuel tank.
In addition, this control function reduces the power consumption of the high pressure pump. This improves the efficiency of the engine.
The fuel metering valve is operated electromagnetically and is closed and opened in a controlled manner via pulse-width modulated signals from the PCM.
The type of pulse width modulation is a function of:
โข Driver’s requirements,
โข Fuel pressure requirement,
โข Engine speed.
1 Fuel supply from the transfer pump
2 Piston
3 Fuel feed from the high pressure pump
Fuel metering valve not actuated
โข When de-energized, the piston closes the passage between the two ports (1) and (3) by means of compression spring force. The fuel supply to the high-pressure pump is interrupted.
1 Fuel supply from the transfer pump
2 Piston
3 Fuel feed to the high pressure pump
4 Coil energized
5 Fuel volume
6 Control current
7 Fuel metering valve characteristic curve at constant engine speed.
Fuel metering valve actuated
โข The valve coil is energized by the PCM in accordance with the engine requirements. The armature force is proportionate to the electrical control current and acts against the compression spring via the moving piston.
โข The aperture between the two ports (1) and (3) and consequently the fuel quantity supplied to the high pressure pump via the port (3) is also proportional to the control current. This means that the greater the cross section of the aperture, the greater the fuel quantity supplied.
Effects of faults
NOTE: When de-energized, the fuel metering valve is closed.
The fuel metering valve operates together with the high pressure control valve and the fuel pressure sensor on the fuel rail in a closed-loop control circuit. Depending on the extent of the fault, either a limited operation program is activated, or in the case of serious faults, the injected fuel quantity is set to 0 (engine cuts out or does not start).
Diagnosis
In the Siemens strategy, the fuel metering valve, the fuel pressure control valve as well as the fuel pressure sensor operate in close interdependency and should therefore not be treated separately during EOBD fault analysis.