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What is a fuel Injector?

By: Don Bowman

How do fuel injectors work?

Fuel injectors are small electro-mechanical devices that are used to spray fuel into the intake manifold directly in front of the intake valve. The injector has a final high micron filter in the top inlet side and small hypodermic-sized holes on the bottom for the atomizing of fuel. The fuel acts as a lubricating agent for the injector. Water in the fuel is extremely damaging to the injectors due to the fact that it displaces the lubricating properties of the fuel.

Injectors open and close at the same rpm as the engine for a two stroke, and at half the engine RPM for a four stroke. This equates to more than 138,000 times an hour. Fuel injectors are subject to carbon and dirt introduced by a bad air cleaner element. The type of fuel used and the grade as well as the additives directly effect the life expectancy of the injectors. The computer controls the fuel injectors. They have power continuously when the key is turned on. In essence, the computer grounds the injector, completing the circuit and causing the injector to open. When the ground is removed, the injector closes. The computer, after receiving information from the various sensors, determines the length of time the injectors need to be grounded to inject the correct amount of fuel given the demand.

The average fuel injector duty-cycle is measured in terms of milliseconds. The average is 1.5 to 6 milliseconds. Fuel injectors come in different sizes depending on the cubic inches and power demands of the engine. There are two basic types of fuel injectors. The first is the oldest version, which is the throttle body injection. This essentially is a system where one or two fuel injectors are located in the throttle body itself. They supply all the cylinders with a metered amount of fuel misted into the intake manifold. This charges the intake and the intake valve draws the fuel into the cylinder. This system was the most widely used system. More efficient than a carburetor, since it could adjust to air density and altitude and was not reliant on manifold vacuum, it was not as efficient as direct individual port-type fuel injection. The reason for this is that the cylinders closest to the injectors had a better mixture than the ones farthest away. Individual port type injection has eliminated this flaw by injecting the same amount of fuel to each cylinder. (click for enlarged photo)

Some of our favorite injectors are the following:

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