CRD (Bosch) quantity control valve

The purpose of this test is to evaluate the operation of the Bosch Common Rail Diesel (CRD) Quantity Control Valve (QCV) based on the voltage and duty control under engine run conditions.

How to perform the test

View connection guidance notes.

1. Using manufacturer's data, identify the fuel rail pressure regulator valve control signal circuit.
2. Connect PicoScope Channel A.
3. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
4. Start the scope to see live data.
5. Turn on the ignition and wait for the glow plug light to extinguish (if applicable).
6. Start the engine.
7. With your waveforms on screen stop the scope.
8. Turn off the engine.
9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Example waveform

Waveform notes

This known good waveform has the following characteristics:

• A switched earth, pulse-width modulated (PWM) signal having a fixed cyclic period in which its voltage switches between battery positive at around 15 V and close to battery negative at just above 0 V.
• The percentage of the total cycle period spent at 0 V indicates the PWM duty. Approximately two-fifths of each cycle is spent close to 0 V, indicating that the PWM duty is around 40%.
• Nearly one waveform cycle is completed every 5ms, indicating that the cycle frequency is just under 200 Hz.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select MPROP Valve voltage.

Further guidance

Within a common rail diesel system, the Engine Control Module (ECM) uses a quantity control valve to regulate the fuel pressure entering the common rail via the high pressure pump: when the ECM needs to reduce the pressure, the valve is closed and less fuel is drawn through the pumping mechanism, excess fuel is released to the fuel return system. Conversely, when an increased pressure is needed, the valve is opened and an increased quantity of fuel is delivered through the pump.

A quantity control valve position is determined by the action of a solenoid against a spring. With these devices the valve will move from its default position when current flows through the solenoid. Default may be either open or closed depending on the application. The greater the current, the greater the displacement of the valve. Thus, in some systems an increase in current will cause the valve to become more closed, whereas in others it will cause the valve to become more open.

An ECM can efficiently control current in a circuit using a PWM signal and, for a given electrical load, the greater the duty period, the amount of ON time relative to the whole cycle, the greater the average current flowing through the circuit.

With a switched earth activated circuit, the solenoid is fed with a constant battery positive on both terminals and the ECM controls the path to earth creating current flow. Therefore, the valve is energised on when the actuation signal is at battery negative and de-energised off when the actuation signal is at battery positive. Hence the greater the duty cycle, the greater the current in the circuit and the greater the displacement of the valve from its default position.

The ECM will vary the duty depending on engine speed, load, temperature conditions and the torque demand from the driver accelerator pedal position.

By reducing the quantity of fuel entering the high pressure pump and common rail system, the loads on the pump and engine, are reduced, helping to increase the efficiency of the engine.

Refer to vehicle technical data for specific test conditions and results.

GT056-EN