Bosch-Common Rail System – Fuel metering valve (CP3.2)

The fuel metering valve regulates the fuel quantity which is fed to the high-pressure chambers of the high-pressure pump depending on the fuel pressure in the fuel rail.

As a result, the quantity of fuel that flows back to the fuel tank is kept to a minimum.

1 Coil
2 Wiring harness connector connection
3 Valve needle
4 Valve closed
5 Maximum opening cross-section
6 From the transfer pump
7 To the high-pressure chambers

NOTE: The fuel metering valve is fully opened in its de-energized state.

The fuel metering valve is controlled by PWM signals from the PCM. The type of pulse width modulation is a function of:

• Driver’s requirements,
• Fuel pressure requirement,
• Engine speed.

The fuel metering valve operates together with the fuel pressure sensor on the fuel rail in a closed control loop.

Effects of faults

In the event of serious malfunctions, the injected quantity is set to 0 and the engine cuts out or cannot be started.

Malfunctions in the fuel metering valve are detected by continually comparing the fuel pressure request (calculated by the system) and the actual fuel pressure (measured in the fuel rail). In the event of a deviation from a set tolerance range, the injected quantity is set to 0 and the engine cuts out or cannot be started.

Diagnosis

The EOBD requirement demands the detection of faults when determining the injected fuel quantity and fuel injection timing. These parameters have serious effects on the exhaust gas emissions.

The determination of the fuel injection timing is established via the crankshaft position.

The injected quantity results from the engine speed and the opening time of the fuel injector, depending on the fuel pressure in the fuel rail.

Monitoring of the fuel pressure is a function determined by the interaction of the fuel metering valve (adjusting the delivery quantity for the fuel rail) and the fuel pressure sensor (adjusting the desired fuel pressure).

From the output shape of the pulse width modulated signals, the monitoring system identifies (by comparing it with the target map data) whether the actuation is within the limits.

The Bosch diagnostic system classifies faults in the fuel metering valve either

• as control faults (in this case the engine speed is limited to a safe range) or
• as malfunctions (in this case the engine is switched off by the PCM).

In addition, short circuits (to ground and battery) and open circuits are monitored. Control faults only have minor effects on exhaust gas emissions. Consequently, this is a non MIL active component, as the EOBD limits are not exceeded. Malfunctions result in the engine being stopped by the PCM; this ensures that the exhaust gas emissions are not affected.

Possible diagnostic trouble codes: P0191, P0192, P0193, P0251, P0252, P0253, P0254.

08. August 2018 by Ron
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