It is an injector with a lift sensor. It tells the ECU when the injection cycle is happening compared to the crankshaft position - and that is the extent of my knowledge on that subject![/quote Yep,when the injector commences injection it squashes a piezo crystal which outputs a small voltage - can be viewed on a scope.The engine ecu uses this info along with the 36-1 waveform from the crankshaft position sensor to calculate actual injection timing and can advance or retard the pump timing.This is after comparing other sensor values such as coolant temp,boost pressure,driver demand etc,etc.
It is also used in the event of the crank sensor failing,which results in a high idle speed as it is not as accurate as the crank sensor esp on overrun as fuelling is completly shut off.
B.T.W. Stew,why are you replacing the injector ?