A method of controlling the operation of an engine fuel system including at least one fuel injector, a high pressure fuel pump for delivering fuel to the injector and a pressure sensor arranged to provide an output signal indicative of the pressure of fuel delivered to the injector, comprises the steps of controlling the rate of flow of fuel delivered from the pump to the injector by means of a metering valve arrangement supplied with a control current, measuring the speed of the engine and monitoring the status of the pressure sensor so as to determine whether a fault condition has occurred within the sensor. In the event that a fault condition has occurred in the pressure sensor, the control current supplied to the metering valve arrangement is varied in response to the measured engine speed signal so as to maintain operation of the engine at a substantially constant, predetermined engine speed. The invention also relates a fuel system for implementing the control method.