Patent ID: 7497205

Claim:
A controller for determining the presence of faults within a fuel injection system of an engine system, the engine system comprising a first injector and at least one further injector, each injector comprising a needle control valve and a pressure control valve, and the controller comprising: inputs for receiving data relating to a first engine system parameter; outputs for outputting a control function for controlling the injector valves of each of the injectors, and; a processor for controlling the control function output from the controller wherein the processor is arranged to output a control function such that the needle control valve of the first injector is kept closed in order to prevent injection from the first injector and to monitor the first engine system parameter as the needle control valve is kept closed, a change in the first engine system parameter indicating that the first injector is operating substantially within normal operating parameters and no, or substantially no, change in the first engine system parameter indicating that the first injector is faulty; wherein the processor is arranged to output a control function to close the pressure control valve in such a manner that, under normal injector operating conditions, the pressure within the first injector would increase, and to monitor said first engine system parameter in order to determine the presence of a fault in the valves of the first injector; wherein the processor is arranged to monitor the first engine system parameter and to determine (i) that the needle control valve is biased closed it the engine speed decreases; or (ii) that the needle control valve is biased open if the engine speed increases.