How a Fuel Injector Works

While older cars used carburetors to control the flow of fuel to the engine, if you have a modern car it is almost guaranteed that the fuel traveling from the gas tank to the engine chamber is regulated by a fuel injector. Fuel injectors are a complex nozzle and valve that are designed to very accurately regulate the amount of fuel that your car's engine receives. If you are making any decisions about your fuel injectors, whether you are replacing them, upgrading them, or repairing them, it is important to know exactly how they work. What follows should give you a good understanding of the basics of how a fuel injector works.

Basics of Operation

A fuel injector, in the simplest terms possible, is a valve that controls the amount of fuel that enters one of your engine's chambers. Fuel injectors must control the amount of fuel that your engine uses very carefully to avoid inefficiency.

However, a fuel injector cannot choose the right amount of fuel to use, or sense how much is actually needed. In order to accomplish these important tasks, the fuel injector must take commands from the engine control unit, or ECU.

Example of Use

When you push down on the acceleration pedal in your car, you are adding oxygen to your engine's chambers. When the engine control detects that the acceleration pedal is down, by checking the throttle valve to see if it is open, the engine control unit uses its sensors to determine how much you are adding, and calculates the correct amount of fuel that the fuel injector needs to add to the chamber. Once it has done this, it can control the fuel injector.

When the engine control unit powers up the fuel injector, it causes an electromagnet to turn on. This electromagnet controls the opening and closing of the fuel injector's nozzle.

The fuel injector itself has a supply of fuel. This fuel is supplied by an external pump, and it is kept under pressure. The pump pushes fuel through the fuel rail, which is a pipe leading to the fuel injectors. When the engine control unit causes the electromagnet to open the fuel injector's nozzle, the fuel that is under pressure inside the fuel injector is forced out.

The nozzle of the fuel injector is specially designed to effect this process. As pressurized fuel is forced through it, it turns the fuel into a mist that burns more easily.

After this, the electromagnet is turned off, causing the nozzle to close once again. The engine control unit also controls this process. The duration for which the electromagnet is on—and therefore, the duration for which the nozzle is open and fuel can be pushed out—is calculated very specifically by the engine control unit. This unit of time is referred to as the pulse width.

Once this happens, the process repeats itself. At this point, the engine control unit checks the amount of unused oxygen that is coming out in the exhaust, and uses this information to vary the pulse width so that greater efficiency is achieved.