How Does A Fuel Injector Really Work?

Fuel injectors have found their way into engines of all sizes due to technological changes. If you look closely, they can be found on everything from modern automotive engines to chainsaws. Knowing how a fuel injector works is more important in this time than knowing how to read a cam card or adjusting the idle of a Rochester Quadra Jet carburetor.

To work correctly the fuel system simply needs to do 3 things correctly.

  1. Inject fuel at the correct time
  2. Inject the correct amount (quantity) of fuel
  3. Inject the fuel for the correct length (injector pulse)

I will agree that these three things seem very simple for the automobile to do. But let’s do some quick math to see how quickly this needs to be done.

A modern four cylinder engine equipped with SEFI (Sequential Electronic Fuel Injection) will fire each cylinder once every two engine revolutions.

Fuel Injector Pulses Per Minute = engine rpm/2

On an engine cruising down the road at 1500 RPM, that means the injector is firing 750 every minute or 12.5 times per second.

Modern engine control modules (ECMS) are able to complete this task with ease.

The fuel injector is the muscle for the brain of the operation, the ECM.

How does a fuel injector work?

The fuel injector is only one component of the modern vehicles fuel system. Remember before how I was telling you the fuel injector is the muscle and the ECM was the brain?

Well, the fuel pump would be considered the heart of the fuel injection system. The fuel pump creates pressure and allows fuel to flow through the fuel system. Very much like your your heart pumps blood through your body. Think of the veins as fuel lines.

The fuel lines allow fuel to flow from the tank to the fuel rail. The fuel injector is supplied a steady constant supply of filtered fuel so it can do its job when commanded to.

When the fuel reaches the fuel injector it has been regulated. This means the pressure is set by a fuel pressure regulator. The regulator can adjust for varying driving conditions and power requirements when the engine requires at that specific moment in time.

The fuel injector is connected to the fuel rail as well as the intake manifold with two O-rings, one located on the fuel rail.

The other is used to seal the connection between the intake. It is important for these areas to be sealed to prevent unmetered and unfiltered air from entering the engine.

The fuel injector itself is a small work of technical wonderment.

Yes, it is complicated but let’s take you through step by step to let you completely understand what is going on. Please refer to the image to help your understanding, how does a fuel injector work.

Fuel Injector How To : Step By Step

Photo By:

A port fuel injector is shown in the image. The many individual components are shown in the image to help you identify the components as we begin to understand how the injector works.

Step 1:

Fuel is supplied to the fuel injector before anything happens. This means that clean pressurized fuel is available at all times when the vehicle is cranking/running. It is directed into the fuel injector body through the connector and runs through the filter at the top of the connector. This fuel is blocked from exiting the fuel injector by the needle pintle which is located at the bottom of the needle. This needle pintle along with the seat form a seal which prevents pressurized fuel from exiting the injector and being injected into the intake of the engine.

Step 2:

The fuel injectors uses a solenoid and the magic of magnetism to function. This electrically operated solenoid in the image is referred to as a coil.

Step 3:

At the correct moment that the PCM determines it will provide a power and ground to the injector. This will cause the coil to magnetize. This magnetic field will than draw the needle upward lifting the needle pintle from the seat.

Step 4:

The movement of the needle pintle from the seat provides an area for the fuel to exit from the injector. This pressurized fluid travels through the seat and through the orifice disc.

Step 5:

A close up illustration of a fuel injector orifice disc helping to show how a fuel injector works.

The orifice disc does the important job of turning the fuel into a highly atomized spray. The fuel needs to be atomized to ensure proper combustion when the air/fuel mixture is ignited.

Step 6:

The PCM turns off the injector by opening the circuit, this causes the magnetic field in the injector to collapse. The needle pintle will than be forced downward by spring pressure to seal the pintle and seat before the next injection sequence begins.

Step 7: This task is completed in 1-10 mS depending on engine load and design of the injector.

The fuel injector really is the unsung hero of the engine. Imagine all of this occurring in such a small component 12.5 times per second!

Fuel Atomization Is Needed

Two fuel injectors, one showing a good spray pattern the other showing a bad spray pattern.

While liquid fuel does not burn well, fuel vapors are easily burned. So, the fuel injector needs to make sure that the fuel entering the intake is atomized.

What does atomized mean?

No, we are not going nuclear inside of the engine. Atomized simply means that the fuel entering the engine is in the smallest possible form. Think of millions of tiny little droplets of fuel rushing through the intake system.

The fuel injectors orifice disc make sure that the fuel is atomized and properly injected into the engine.

The orifice disc contains many small holes. Fuel atomization occurs, when fuel is forced through these holes at high pressure.

Not only does the orifice disc allow the fuel to atomize it also gives the injector a cone like spray pattern.

The orifice tube and filter assembly of the injector are common symptoms of a faulty fuel injector.

John Morris
John Morris
John Morris is the technical editor for His years of experience in automotive repair as well as an automotive professor have prepared him to ensure that even the most technical information is accurate and concise at all times.

Latest Articles