A method of determining the nature of a fault in the operation of a hydraulic fuel injector includes sending an actuation pulse to an actuator of the injector, the actuation pulse being above the minimum drive pulse of the injector. The method also includes analyzing a signal from an accelerometer of the injector to determine if there is a high frequency vibration component subsequent to the end of the activation pulse. The method also includes determining the functionality of a needle control valve of the injector dependent on the outcome of analyzing the signal from the accelerometer.

An electrical connector includes two lateral mounting bush. A knock sensor which delivers data representative of the operation of a fuel injector is integrally overmoulded in one of the mounting bush. The knock sensor includes a piezoelectric member arranged between a base member and a seismic member.

A method of determining the nature of a fault in the operation of a hydraulic fuel injector includes sending an actuation pulse to an actuator of the injector, the actuation pulse being above the minimum drive pulse of the injector. The method also includes analyzing a signal from an accelerometer of the injector to determine if there is a high frequency vibration component subsequent to the end of the activation pulse. The method also includes determining the functionality of a needle control valve of the injector dependent on the outcome of analyzing the signal from the accelerometer.

A fuel injector includes a noise sensor fixed to the body fixed on the injector body to record knocks relevant to the end travel of a control valve and of a needle.

An electrical connector includes two lateral mounting bush. A knock sensor which delivers data representative of the operation of a fuel injector is integrally overmoulded in one of the mounting bush. The knock sensor includes a piezoelectric member arranged between a base member and a seismic member.

A fuel supply device includes: a linear actuator; a reciprocating pump having a boosting piston driven by the linear actuator, configured to axially reciprocate, and configured to alternately repeat suction of the fuel and ejection of the fuel more boosted than the fuel at a time of suction by reciprocation of the boosting piston; and a controller to control driving of the linear actuator. When reciprocation amplitude of the boosting piston is A (A>0) and a reciprocating cycle time is T, the controller controls the linear actuator so a maximum value of an absolute value of acceleration when the reciprocating pump sucks the fuel with an absolute value of speed of the boosting piston increasing is smaller than A.Math.(2/T).sup.2, and so a maximum value of the absolute value of the acceleration of the boosting piston when the reciprocating pump ejects the fuel is larger than A.Math.(2/T).sup.2.

A header for a fuel injector is connectable to a fuel injector main body, wherein the header includes a sensor adapted to measure one or more parameters of the fuel injector during operation thereof.

A fuel supply device includes: a linear actuator; a reciprocating pump having a boosting piston driven by the linear actuator, configured to axially reciprocate, and configured to alternately repeat suction of the fuel and ejection of the fuel more boosted than the fuel at a time of suction by reciprocation of the boosting piston; and a controller to control driving of the linear actuator. When reciprocation amplitude of the boosting piston is A (A>0) and a reciprocating cycle time is T, the controller controls the linear actuator so a maximum value of an absolute value of acceleration when the reciprocating pump sucks the fuel with an absolute value of speed of the boosting piston increasing is smaller than A.Math.(2/T).sup.2, and so a maximum value of the absolute value of the acceleration of the boosting piston when the reciprocating pump ejects the fuel is larger than A.Math.(2/T).sup.2.