Method of calculating leakage in a common rail fuel injection system taking into account a predetermined leakage quantity

The method comprises calculating an injector leakage quantity as a function of a set of input variables and a predetermined leakage quantity. The variables may comprise values for rail pressure, fuel density and electric command duration. The variables may also comprise an operating condition coefficient, mapped as a function of rail pressure, command duration and a ratio between a first injector equivalent area corresponding to the working condition of the leakage quantity and a second area corresponding to the generic condition where the leakage quantity is estimated. The operating condition coefficient may depend on injector design and is evaluated across a batch of injectors. The input variables may further comprise a value for fuel density, based on fuel temperature and rail pressure. The fuel injector may comprise a solenoid or piezoelectric actuator. The method may be carried out by an electronic control unit using a computer program.