US Patent 8000876 Fuel injector control

A method of operating a fuel injector having a piezoelectric actuator that is operable by applying an electrical drive pulse thereto to activate and deactivate the injector. The method includes monitoring an electrical characteristic of the actuator during a predetermined time period, determining a time-domain data sample corresponding to the monitored electrical characteristic during the predetermined time period, determining a frequency spectrum signature corresponding to the time-domain data sample, and comparing the frequency spectrum signature of the monitored electrical characteristic to a predetermined frequency spectrum signature indicative of an injector event.