Fuel Pressure Control Valve (FPCV)

General description
Most common rail systems now employ a pressure regulation valve. This can be located either on the high-pressure pump or on the common rail itself. The pressure regulation valve serves with the quantity control valve to control the common rail pressure. 
The pressure relief valve simply allows more or less high pressure fuel to flow into the back leak system thus increasing or decreasing the fuel pressure in the rail. Excess fuel returns to the fuel tank. It’s controlled from the ECM. 
Appearance
Fig. 1 shows how the fuel pressure control valve looks like.

Fig. 1

Principle of operation of the fuel pressure control valve

The pressure control valve uses a PWM electrical signal to regulate fuel pressure in the fuel rail. A closed loop feedback circuit exists between the rail pressure sensor and the fuel pump regulator. A direct current pulse width modulated signal applied to the pressure regulator determines how much fuel is either supplied to the pump, returned to the tank or pump inlet based on the signal from the rail pressure sensor. The fuel pressure control valve operates on a duty-cycle of between 5 and 95%. The higher percentage of duty-cycle corresponds to a lower the pump pressure. This means if the pressure regulator should lose its signal, it will operate at a wide-open or default value and the engine will continue to operate although run roughly. The optimum value for injection pressure is coordinated by the ECM according to the engine speed and load conditions. With some engine management systems, the pressure regulator acts as a fuel temperature sensor. Resistance of the coil within the regulator is proportional to fuel temperature and permitting fuel temperature to be inferred from the actuators resistance. Two fuel rail pressure regulators (FRPR) are used on the 2010 DMAX. The first remains located on the injection pump. A second regulator is located on the front of the left fuel rail and has a normally open solenoid. A pulse width modulated is applied to this regulator to control the amount of fuel returned to the fuel tank. Two regulators are used for OBD-II fuel system monitors. Excess return flow from injectors indicates a problem with worn nozzle valves or defective actuators.

Order to verify functionality of the fuel pressure control valve
• Testing the fuel pressure control valve by oscilloscope

Voltage vs Current

1. Set the first oscilloscope input to 20/
2. Connect the signal test lead (1:1) of the first oscilloscope channel, to one of the valve terminals.
   Then connect the ground lead to the chassis ground.
3. Connect an AC/DC current clamp to another oscilloscope channel.
   Set the AC/DC current clamp range to ±20A.
   Important note: Only one of the two wires should be clamped, and not both of them. 
   It doesn’t matter which wire will be clipped with the current clamp: the positive or the negative one. 
   This will only affect the polarity of the measured current.
4. Start the engine and left it idling.
5. Watch the oscilloscope screen. Compare result with the waveform in fig.2.

Fig.2

Voltage

1. Set the first oscilloscope input to 20/
2. Connect the signal test lead (1:1) of the first oscilloscope channel, to one of the valve terminals.
   Then connect the ground lead to the chassis ground.
3. Start the engine and left it idling.

Fig. 3

• Possible failures in the fuel pressure control valve

• Mechanical fault
• Broken valve solenoid
• Missing control signal

• Other checks:

• Check for mechanical damaged parts of the engine, ignition system or in the fuel system.
• If a signal error is present, test the wiring from the engine control unit to the pressure regulation valve.
• Ensure that the engine control unit (ECU) has good power supplies and grounds where required.