Fuel Rail Pressure Control Valve The fuel rail pressure control valve is located on the high pressure fuel pump. The control valve regulates the fuel pressure within the fuel rail and is controlled by the ECM. The control valve is an electrically operated solenoid valve which is either open or closed. When the solenoid is de-energised, an internal spring holds an internal valve closed. At fuel pressure of 100 bar (1450 lbf/in 2 ) or higher, the force of the spring is overcome, opening the valve and allowing fuel pressure to decay into the fuel return pipe. When the pressure in the fuel rail decays to approximately 100 bar (1450 lbf/in 2 ) or less, the spring force overcomes the fuel pressure and closes the valve. When the ECM energises the solenoid, the valve is closed allowing the fuel pressure to build. The pressure in the fuel rail in this condition can reach approximately 1300 bar (18854 (1450 lbf/in 2 ). The ECM controls the fuel rail pressure by operating the control valve solenoid using a PWM signal. By varying the duty cycle of the PWM signal, the ECM can accurately control the fuel rail pressure and hence the pressure delivered to the injectors according to engine load. This achieved by the control valve allowing a greater or lesser volume of fuel to pass from the high pressure side of the pump to the unpressurised fuel return line, regulating the pressure on the high pressure side. The fuel rail pressure control valve receives a PWM signal from the ECM of between 0 and V. The ECM controls the operation of the control valve using the following information to determine the required fuel pressure: l Fuel rail pressure l Engine load l Accelerator pedal position l Engine temperature l Engine speed. In the event of a total failure of the fuel rail pressure control valve, the following symptoms maybe observed: l Engine will not start l Severe loss of power l Engine stalls. In the event of a partial failure of the fuel rail pressure control valve, the ECM will activate the solenoid with the minimum sampling ratio which results in the injection quantity being limited.