Understanding fuel injection system in automobile engines

Do you know how fuel is supplied into the combustion chamber in automobile engines? Am sure you not thinking of a carburetor but a fuel injector. They are now bygone most especially for internal combustion engines. An effective process used is known as a fuel injection system.

Fuel injection is the introduction of fuel in internal combustion engines, mostly automotive engines, using injectors. This process was introduced to keep up with emissions and fuel efficiency laws. Over the year, car manufacturers saw great advantages of fuel injectors which is where the downfall of carburetors begins.

From 1980 onward fuel injection become an alternative to carburetors on petrol engines. Well, the difference between fuel injection and carburetion is that fuel injection atomizes the fuel through a small nozzle under high pressure. Whereas, carburetors rely on drawing fuel into the airstream through a venturi tube.

fuel injection system in automobile engine

Research has shown all diesel engines use fuel injection by design. Gas engines can use gasoline direct injection, where fuel is directly delivered into the internal combustion chamber. Indirect injection can also be used, where the fuel is mixed with air before the intake stroke.

Today we’ll be looking deep into the definition, functions, parts, types, working principle, and problems, as well as the advantages and disadvantages of fuel injector systems in automotive engines.


What is a Fuel Injector?

Fuel injectors are small nozzles that are controlled electronically to atomize fuel under high pressure in an engine’s combustion chamber. It contains valves that are capable of opening and closing many times per second.

Before the existence of fuel injectors, carburetors have been highly used on engines, and to date, this engine still exists.  In fact, many other machines like lawnmowers and chainsaws still use carburetors. But because the component got complicated trying to control all requirements on automobiles, a better alternative is released.

Carburetors were first replaced with throttle body fuel injection systems. This system is also known as a single-point or central fuel injection system. It is electrically controlled fuel-injector valves into the throttle body.

This was almost the best alternative, which allowed auto manufacturers don’t have to make drastic changes to engine designs. Gradually, as new engines were designed multi-port fuel injection replaced the throttle body fuel injection. This multi-port fuel injection is also known as port, multi-point, or sequential fuel injection.

The system contains a fuel injector for each cylinder which sprays right to the intake valve. It provides more accurate fuel metering and quicker response.

Functions of fuel Injector 

Below are the functions of fuel injectors in an internal combustion engine:

  • The primary purpose of fuel injection systems in diesel engines is that their design is heavily influenced by the components,
  • Fuel injectors help to deliver fuel to the cylinders.
  • It enhances the engine in terms of performance, emission, and noise characteristics.
  • Fuel is delivered under extremely high injection pressures.
  • Its materials are designed to withstand higher stresses for durability that match the engine working.
  • Another purpose of the injection system is that fuel is injected at the proper time. That is, the injection timing is controlled.
  • The correct amount of fuel must be delivered to meet the power requirement of the engine. This is why the injection metering is controlled.
  • Injectors are made of greater manufacturing precision and tolerance to ensure their working efficiency. It also avoids leakage.
  • The fuel injector atomizes fuel into a very small fuel particle ensuring every small droplet of fuel vaporizes and undergoes the combustion process.
  • There is enough oxygen to mix with the atomized fuel which ensures complete combustion.

Read: Difference between fuel injection and carburetor

Major Parts of Fuel Injection System

Below are the major functional parts that enable the working of fuel injection in automobile engines and the names of components in a fuel injector:

The major parts of the fuel injection system are divided into two which include low-pressure and high-pressure sides, the low-pressure parts are the fuel tank, fuel filter, and fuel supply pump. While the high-pressure side includes a high-pressure pump, fuel injector, accumulator, and fuel injector nozzle. The injection nozzle has different actuation designs for various types of fuel injection systems.

As fuel needs to be transferred from the fuel tank to the injector system, the role is a low-pressure fuel system. Whereas, the fuel injector to the combustion chamber is the high-pressure system.  Below is the role of the following parts stated above:

  • Fuel tank – the part where the fuel is stored.
  • Fuel pump – it pumps fuel from the fuel tank to the fuel injection system.
  • Injection pump – this part is a meter and pressurized fuel for injection.
  • Governor – supply fuel in accordance with the load.
  • Fuel injector – supplies fuel from the injection pump to the cylinders.
  • Fuel filter – to filter dirt, duct, and abrasive particles from blocking the injection system.

The image below shows the major parts of a fuel injector:

parts of fuel injector

Fuel injection systems work fully and precisely to provide the correct amount of fuel for every operating condition. The engine control unit (ECU) is used to monitor most parts of the input sensors. Below are a few parts that use sensors for precise working:

  • Oxygen sensor – notes the amount of oxygen in the exhaust, which allows the ECU to determine if the fuel mixture is rich or lean. It makes adjustments accordingly.
  • Throttle position sensor – this sensor monitors the throttle valve position to know how much air enters the engine. The ECU responds quickly to changes, increasing or decreasing the fuel rate as required.
  • Mass airflow sensor – let the ECU know the amount of fuel entering the engine.
  • Coolant temperature sensor – determines when the engine reaches its proper operating temperature to the ECU.
  • Manifold absolute pressure sensor – determines the pressure of air in the intake manifold.
  • Engine speed sensor – monitors the engine speed, which is why it is used to calculate the pulse width.
  • Voltage sensor – determines the system voltage in the car to know when the ECU raises the idle speed. this may be when the voltage is dropping which will indicate high electrical load.

Types of Fuel Injection Systems

Below are the common types of fuel injection systems seen in older and modern vehicles:

Single-Point or Throttle Body Injection:

The single-point type of injection system is the earliest and simplest fuel injection that replaces carburetors. It contains one or two injector nozzles in the throttle body, which is the throat of the engine’s air intake manifold. This injector system is not as precise as the system that followed but when compared with carburetors, it has better control, is less expensive, and is easier to service.

Port or Multiport Fuel Injection:

In multiport fuel injectors, separator injector nozzles are contained in each cylinder, at its intake port. This is why the system is sometimes called a port injector, shooting the fuel vapor close to the intake spot, ensuring it’s completely drawn into the cylinder. One of the benefits of this injector is that the meter’s fuel is more precise when compared with the single point. It is also perfect for achieving the required fuel-air ratio and it virtually eliminates the possibility that fuel will condense or collect in the intake manifold.

Sequential Fuel Injection:

This type of fuel injector is also known as sequential port fuel injection or time injection. It is a type of multiport injection even as basic multiport uses multiple injectors. They all spray their fuel same time or sequentially, making the fuel hang around for as long as 150 milliseconds when the engine is idling. The benefits of sequential fuel injection are that the system responds more quickly if the driver makes a sudden change. This is because the valve only has to wait for the next intake valve to open, rather than the complete revolution of the engine.

Direct Injection:

Direct injection is common in diesel engines, although starting to be common in gasoline engine designs. It is sometimes called DIG for direct injection gasoline. In its process, fuel is injected directly into the combustion chamber, past the valves. Fuel metering is more precise than other fuel injection types. Direct fuel injection gives engineers another variable to influence precisely how combustion occurs in the cylinders.

The science of engine design examines how air-fuel mixture swirls around in the cylinders. And also how the explosion travels from the ignition point. Direct injection in a gasoline engine can handle things such as the shape of cylinders and pistons. Also, port and spark plug locations, timing, duration, and intensity of the spark. Number of spark plugs per cylinder. All these affect how completely and evenly fuel combusts in a gasoline engine.

Working principle

The working of a fuel injector system is quite interesting and easier to understand. The main work is from the fuel injector to the combustion chamber after fuel is pumped to it from the fuel tank. As earlier said, the fuel injector is an electronically controlled mechanical device that is responsible for fuel spraying. The injector gets energized and an electromagnet moves a plunger that opens the valve.

This valve allows the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel, which is responsible for making the fuel easily burn. The amount of time the fuel injector stays open will determine the fuel supplied to the engine. This is known as “pulse width” and it is controlled by an ECU device. Fuel injector systems are mounted directly to the intake manifold so that fuel can be sprayed directly into the intake valve.

There is a spring inside the conventional injector that holds the needle valve in a close position. It holds this needle valve until the high-pressure line meets a specific value. There is a pipe called a “fuel rail” that supplies pressurized fuel to the injectors. The right amount of fuel is supplied to the required parts.

Different parts of the engine are equipped with sensors that give information to the ECU about the amount of fuel and make adjustments if needed. The various sensor has been listed and explained in the above part of this article.

Watch the video below to have more understanding of the working of the fuel injection system:

Symptoms of Bad Fuel Injectors and How to Prevent Them

Failure occurs on the fuel injector after overworking, and if not regularly maintained, it can develop serious faults or become clogged. Below are the symptoms of bad fuel injectors and how to prevent failures:

  • Rough engine performance
  • Complications while starting the vehicle
  • Fuel odors
  • Oil thinning
  • Failed emission
  • The engine fails to reach the full RPM
  • Poor performance of the vehicle
  • Catastrophic engine failure
  • Smoke emission
  • Increased fuel consumption
  • Pollution

These problems often occur on fuel injector when there is dirty, carbon particles, oil fuel, or an accumulation of residue leading to clogged fuel injectors. Issues happen after the filter basket collects debris that prevents fuel from flowing through it.

The proper way to prevent fuel injectors from failing is regular maintenance. The vehicle’s parts must be inspected on a regular basis. Even though fuel injectors have great tolerances, still inspection should be made on the components.

For more reliable results, adding moisture drawing ethanol or additives, visual supervision, and conducting ultrasonic cleaning. And also, the actual flow pattern for volume and spray testing will help.

Advantages and Disadvantages of Fuel Injection System


Below are the benefits of the fuel injection system:

  • A precise fuel mixture of fuel and air ensures maximum possible fuel efficiency and power production.
  • The combustion process is significantly more efficient in fuel-injected engines.
  • Fuel injection engines are more economical and they maximize and minimize the emission level.
  • Cold starting is eliminated in fuel-injected engines, making no need for manual chocking.
  • It’s also used on modern performance motorcycles.
  • The fuel injection system automatically balances the air-fuel mixture considering the environmental situation.
  • Engine vibration is reduced and the spark plug fouling issue is minimized.


Despite all the benefits of the injection system some limitation still occurs. Below are the disadvantages of the system:

  • It is a complex electronic controlled device that works with few electronic sensors.
  • Maintenance and repair of the system is very limited. That is, not all workshops can do their work.
  • The fuel injection system is quite expensive.
  • Good quality material and fuel are highly recommended.
  • There is no solution for low cost and low capacity.

In conclusion, the fuel injection system has totally replaced carburetors in automobile engines. we’ve discussed its functions one of which is to deliver fuel at high pressure into the cylinder. The fuel injection systems of different types which include throttle body and multi-port, also revealed its component on low-pressure and high-pressure side. it works, symptoms, and advantages and disadvantages of the fuel injection system.

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