Method for the control and diagnosis regarding the operation a fuel injector

In a fuel injector including an actuator operated valve, said valve being located within a valve body, a method comprising determining the condition where, or the point when, there is or is not electrical continuity between two injector components adapted to move relative to one another during operation. two components are i) one end of an actuator and ii) a control valve or valve needle. The method may determine when the gap between the two said components is reduced to zero and/or when there is electrical continuity between the end of the actuator and the valve/needle or proximal portion of the valve/needle. It may comprise the step of determining the point of contact between the end of the actuator and the valve/needle.