Direct electrical signals normally actuate fuel injector timing. The timing controls the opening and closing of spring-loaded hydraulic mechanisms in the fuel injector nozzles. A typical fuel injector system uses electronic monitoring devices and sensors to measure pressure, time and engine strokes.
These monitors are programmed to base a timing mechanism on one or more of these factors. When the device senses it is time to send fuel to the combustion chamber, it sends an electronic signal to a mechanism in the nozzle that opens and closes to release fuel. The device that opens and closes is generally a simple spring-loaded hydraulic device or valve. The actuating device that receives the signal and responds usually is made of an electromagnetic solenoid or active piezoelectric ceramic material.