What Are the Uses and Functions of Fuel Injector?

Fuel Injector

For an internal combustion engine to function, there must be a means to introduce fuel into the engine.


The clever engineering behind the internal combustion engine combines fuel with air.

In the spark-ignition engine, a spark from the plug ignites the compressed mixture, releasing a great force to push the piston down.

The diesel or the compression ignition engines do not need spark plugs, and the ignition is compression.

The fuel injector is used to introduce fuel into the reciprocating piston and rotary piston engines.

Now, you are beginning to understand the engine operating principle. Once you turn your ignition key, fuel is introduced into the cylinder.

Without the introduction of fuel into the engine’s cylinder, there will be no ignition.

The fuel injector is one of the most important components of ignition engines. Fuel injectors replaced the carburetors due to their higher efficiency and fuel control.

Mercedes Benz began using fuel injectors in their passenger cars, particularly the OM 138, a diesel-powered vehicle.

These diesel engines mass-produced by Mercedes Benz became available between the 1930s and the 1940s.

The petrol engines did not witness the introduction of fuel injection until 1950. By 1990, fuel injectors had massively replaced carburetors.

Both fuel injectors and carburetors introduced fuel into the engine. But the fuel injector took it a notch higher by injecting atomized fuel with high pressure using a minuscular nozzle.

The carburetor only relied on the suction pressure produced by the drawn-in air passing through the venturi tube.

The carburetor mixed the fuel and the air before sending it into the engine. Now let us get some basics of fuel injection out of the way.

The air-fuel mixture could be done in two ways, externally or internally. The manifold injection system uses the external system of air-fuel mixture formation.

Now you know what mechanics refer to when they mention the engine’s manifold. Even the manifold injection system is of two types.

The two types of manifold injection systems are the multi-point injection and the single-point injection system.

The multi-point injection is also referred to as port injection, while the single-point injection is also referred to as throttle-body injection.

There are two ways to obtain mixture formation for the internal system. It can either be done directly or indirectly.

A common type of direct injection system is the common-rail injection system. In this system, the fuel injectors are placed on a common rail to service all the engine cylinders.

The direct and indirect internal mixture formation systems have different designs to optimize fuel supply to the engine.

A fuel injector could be electronically controlled, and this electronic control forms the basis of the electronic fuel injection system.

The Fuel Injection System

Three basic components make up all kinds of fuel injection systems. Whether it is the fuel injection system found on that heavy-duty truck or the small cab you just hailed, they all have these three components.

There must be a fuel injector with a component to generate the required injection pressure.

Finally, there will be a component to deliver or meter the right fuel needed for combustion. Now, you can see it is so simple.

Now, here is the fun part. These three components can be different devices on their own, joined together for fuel injection.

You will have a fuel pump, a fuel distributor, and a fuel injector in this manner.

The fuel pump, fuel distributor, and fuel injector can also be partially combined in one form or the other.

In this case, you will have the fuel pump and the fuel injection valve, and the fuel injector and the fuel distributor have been combined to form the injection valve.

All three components could be combined into one single unit in the final form of construction. The single unit is usually referred to as a unit injector.

The early developed mechanical fuel injection systems were usually the partially combined kind.

They had injection valves coupled with either one or multiple helix-controlled fuel injection pumps.

Aside from generating the much-needed injection pressure, the pumps also doubled as the metering device.

These mechanical injection systems were very useful for intermittent fuel injection using multi-points for either direct injection or chamber injection.

However, they fell short of the accuracy needed to improve mileage and efficiency.

Engine manufacturers could incorporate these microelectronic technologies into fuel injection systems with advancements in the microelectronic industry.

They were able to shift the mechanical operation to a fully electronically controlled one.

With the advancements in the electronic control units, the function of metering was taken away from the pump allowing the pumps to be only optimized for providing the injection pressure—what a relief. The pumps were working hard back then.

The modern electronic fuel injection systems are commonly found in multi-point injection systems and among engines that use a common rail.

The common rail injection system is far superior to unit injection systems, and hence, they are the go-to choice for modern vehicle manufacturers.

Why Fuel Injectors are Important

The introduction above must have given you an idea of how important fuel injectors are. I hope you do not mind if I state a few more reasons they are so important.

If that is ok with you, let’s go.

  1. Internal combustion engines need air and fuel to function. They perform better when the quality of the air-fuel mixture is high. The high quality of the air-fuel mixture leads to higher operational efficiency for the engine. A fuel injector offers a far more quality mixture of air and fuel than carburetors could. So, you can ditch that carburetor engine for a fuel-injected one.
  2. Carburetors do not mix the air and fuel properly, and this poor mixture results in the residual deposition of unburned particles inside the engine’s cylinder. These residues most certainly cause incomplete combustion in the cylinder, leading to knocking to the engine. Car manufacturers developed the fuel injection system to prevent incomplete combustion.
  3. Carburetors can not control the mixture of air and fuel. Even though adjustments can be made manually, carburetors do not adhere precisely to the much-needed fuel metering. An electronically controlled fuel injector can provide fuel metering to very high precision to achieve optimal efficiency.
  4. Mileage is higher in vehicles that use carburetors, and this increase in mileage is caused by the unburned residual deposits in the engine’s cylinder. Adopting the fuel injection technology gives better mileage and, overall, a much better performance.

Types of Fuel injectors

Fuel Injector

Once the whole principle of operation was understood, several fuel injectors were developed to enhance efficiency and reduce mileage.

Mileage is probably one of the biggest factors you will consider when making a new car purchase.

Of course, you don’t want to spend a ton of cash filling up the tank in your vehicle. Nevertheless, you still want a highly efficient and reliable engine to carry you and maybe a few extra loads around town and even when traveling.

The throttle body fuel injection, the multi-point fuel injection, including other technologies like the sequential fuel injection all came as a result of advancements in the technology of fuel injection.

All these are used based on intended applications. However, within these categories, there are several options available for fuel injectors.

To fully understand the different types of fuel injectors, let us go through them into categories.

Type of fuel

It is very much obvious that there are two major types of fuels for internal combustion engines—diesel and gasoline. Diesel is a much heavier fuel than petrol, and Injectors have to be specially designed to handle the diesel.

The diesel fuel injectors spray the diesel directly into the combustion chamber of the engine. The packets of diesel sprayed are formed in the capillary and nozzles of these types of injectors.

Diesel injectors use more pumping pressure to inject the diesel into the engine.

Gasoline fuel injectors spray fuel either directly into the combustion chamber of the engine or into the manifold (for manifold injection system).

They usually have smaller capillaries and nozzles than their diesel counterparts.

Metering Control

Fuel injectors have to introduce metered fuel into the combustion chambers. The speed, quantity, and pressure have to be controlled, and the metering control can be done either manually or electronically.

The mechanical control is achieved with the use of springs and plungers. They draw the fuel from the fuel pump or fuel distributor.

Electronic fuel injectors have solenoids responsible for controlling and metering the fuel into the combustion chambers.

Parts of a Fuel Injector

A fuel injector at its basic level is a nozzle. Think of those garden nozzles that water the grass to keep them fresh and green.

The injector sprays fuel the same way, and the only obvious difference is what they spray. While your garden nozzle sprays water, the fuel injector spreads fuel.

We will look at the build-up of both mechanical fuel injectors and electronic fuel injectors. Their purpose might be the same, but their construction differs a bit. Let us begin with the mechanical fuel injectors.

The mechanical fuel injectors have three major components: the injector body, the plunger, and the springs. The shell or the outer body that you see is called the injector body, and all the other parts are specifically arranged within the shell.

The outer body is designed to hold the precise capillary that will carry the fuel, which is highly pressurized from the fuel pump.

In the design, there is no allowance for play. The plunger opens or closes the nozzle.

The plunger is located at the nozzle. It works based on the pressure from the incoming fuel, and it is guided by the fuel distributor.

Now, to plunge and return to the previous position, springs are used. There are two types of springs found in the mechanical fuel injector; the plunger spring and the mainspring.

The plunger spring controls the back and forth movement of the plunger. The increase in fuel pressure in the capillary opens up the nozzles.

Once the fuel is released, the spring returns the plunger to its original position. This closes the nozzle. This is carefully crafted and technically positioned to achieve this simple motion.

The mainspring controls the inlet through which fuel flows into the injector capillary. The pressure required to control this spring comes from the incoming fuel as it is pressurized from the fuel pump.

Electronic fuel injectors are designed to be smart. This means they can vary the amount of fuel injected based on the command they receive from the vehicle’s electronic control system. You will mostly find these types of injectors in modern vehicles.

Electronic fuel injectors share many similarities with the mechanical type, and they have the same components. But for electronic control, the electronic fuel injector adds a few more components.

The components include the injector body, the plunger, springs, electromagnet, and the electronic plug.

The injector body performs the same function as the injector body in the mechanical type. The plunger also performs the same opening and closing of the nozzle, but it is electronically controlled using electromagnets.

The electromagnets are positioned around the plunger, and they control the opening and closing of the nozzle. They are connected to the electronic control unit of the vehicle’s engine, and they have electronic plugs by which wires from the engine control unit are connected.

The electronic control unit controls when the nozzles open, how long they open, and when they close. It is a highly synchronized operation that is much more efficient than the mechanical type.

They respond almost instantaneously to increasing demand from the gas pedal. Now, which one would you like to have? The mechanical type or the electronic type?

The choice is yours. The electronic fuel injector will help you achieve better mileage as it is electronically tuned. However, modifying the system is more technically demanding, and you will need a certified technician.

Working Principle

We have a clear understanding of what fuel injectors do and what components make up a fuel injector. Now, let us look at the technically fun part.

Further down, we will answer the pending question in your mind, how do they work?

Since the electronic type varies from the mechanical type, we will approach their principle of operation differently.

Mechanical fuel injectors

Fuel injectors begin their work as soon as the ignition comes on. This means as soon as you slot in your key and attempt to start the vehicle, they begin operations. The fuel pump immediately sends fuel to the distributor.

The distributor regulates the amount of fuel to be injected and the timing for injection. The distributor then sends the metered fuel to the fuel injectors through the available fuel lines.

The inlet of the fuel injector is forced open due to the high pressure of the incoming fuel.

The mainspring controls the opening of the inlet. As the highly pressurized fuel flows through the capillary, it pushes the plunger, which in turn opens the nozzle.

With the nozzle opened, the fuel is sprayed into the combustion chamber as the case may be.

As soon as the fuel is sprayed, there is a drop in the pressure in the nozzles. The plunger spring then goes back to its original position, closing the nozzle in the process.

The spraying of the fuel stops, and the cycle is completed. The spraying cycle continues as the engine is running.

The fuel pump sends fuel to the distributor, and the distributor sends it to the different fuel injectors for the different engine cylinders.

Electronic fuel injectors

As soon as the ignition is on, the vehicle’s electronic control unit comes alive. Any fault on the engine control module might prevent the engine from starting.

As described above, the fuel pump sends highly pressurized fuel to the distributor.

Now, since it is electronically controlled, the engine control module controls the timing, pressure, and delivery of fuel to the injectors. The module sends the signal to the fuel injectors through the electronic connectors.

The electromagnets in the injectors receive the signal from the engine control module and become activated. The activation of the electromagnets pushes the plunger spring, which opens the nozzles.

The fuel is then sprayed into the combustion chamber or cylinder.

Once the process is completed, the signal from the engine control module is withdrawn, and the spring goes back to its original position, closing the nozzle in the process.

The spraying of fuel stops, and the cycle is completed.

Signs of a bad fuel injector

Well, fuel injectors are not designed to last forever. Is there anything that can last forever? I am yet to find that out.

If you have any ideas on what could last forever, please drop a comment and share this article with your friends to see what they think.

I am extremely grateful that you have read up to this point. This is going to be my bonus tip to you.

Next time your friend’s car demonstrates some of the symptoms I am about to discuss, you will quickly know to check the fuel injector. Just imagine that, and you will be like the pros.

A faulty fuel injector can impact the car’s performance and mileage. In severe cases, it could lead to a breakdown of the vehicle. These signs do not conclusively point to a faulty fuel injector. But it is worth checking them during troubleshooting.

Check engine light

This is one of the most common signs and probably the earliest. The check engine warning light on your dashboard comes on. This is an indication that there is something wrong with the powertrain system.

This light will surely come on as soon as there is a fault with even just one fuel injector. The light is triggered by the electronic control unit that has received a signal from the faulty fuel injector.

The fault could be that the fuel injector injects too much or too little fuel. In addition, it could be that the injector is not even injecting fuel at all.

Engine misfire

Sometimes, you can identify a misfiring engine from the sound it makes. This is usually the case when multiple cylinders are misfiring.

Engine misfires can cause unwanted vibrations from the engine.

Another way of identifying this is when there isn’t a sharp engine response to the pressure applied on the gas pedal. One of the most common causes of this is a blocked nozzle on the fuel injector.

Based on its programming, the electronic control unit requires a certain amount of fuel to initiate complete combustion. When the injector can’t inject the required amount, this will lead to a misfire.

This is why it is important always to keep the fuel injectors clean.

Rough Idling noise

An idling engine should produce a smooth sound. Once the sound changes from smooth to harsh noise, the injectors’ fuel delivery may be short of what is required. Again, this is normally caused by a blocked fuel injector.

Other causes of this could be bad air or a faulty spark plug.

Engine Stall

Let us look at this illustration. You are driving, and your engine suddenly goes off. That is engine stalling. The electronic control unit will immediately turn off the engine if too little fuel gets into the chambers.

It is important to check your fuel injectors when this happens, among others.

Fuel leakage

If there is a fuel leakage coupled with the other symptoms mentioned so far, it is wise to stop the car and do a thorough check.

The fuel could leak out from the injector itself or a loose connection between the injector and the fuel line.

If there is a leak, you will likely find fuel on the injector or close to where the injector is. Fuel leaks are dangerous and costly. Your tank will get empty, and you will be left wondering whether you just drove across continents.

Poor mileage

If your engine suddenly starts returning poor mileage, it might be time to check those fuel injectors. Poor mileage can be caused by increased demand for fuel from the electronic control unit.

If the injectors are clogged and outrightly faulty, you will likely experience poor fuel economy.


Simple, routine cleaning of your fuel injectors with a reliable fuel system cleaner could save you a trip to the mechanic shop. They also help keep emissions low to allow you to pass the MOT and, of course, keep the environment free of pollutants.

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