Fuel from the fuel rail, under pressure, is sprayed in a very fine miss from the tip of the injector. To achieve this, a current must flow through the fuel injector electrical field coils. Contrary to popular belief, this is NOT done by sending power to the injector. Fuel injectors are normally fed power whenever the ignition key is on, but the circuit is not completed and therefore the injector is still close. The computer controls the ground side of the circuit. When the computer provides the injector with a ground, the circuit is completed and current is allowed to flow through the injector. This energizes an electromagnetic coil inside the injector, which pulls a sealing mechanism such as a pintle, ball, or disc away from its seat. This makes it possible for fuel to flow through the injector and into the engine. When the computer removes the electrical ground to the injector, the electromagnetic coil becomes demagnetized and a spring forces the pintle, ball, or disc shut to cut off fuel flow. Even at an engine speed of just 1000 RPM, this is done hundreds of times per minute.
