How the fuel injection system works in your car

Avto 23 January, 2020


If you’ve ever wondered how your car processes fuel within the engine and creates enough energy to propel your car forwards, you’ve come to the right place.

In most vehicles, a fuel injection system is in place to ensure that the engine can run smoothly. These systems are in place in most internal combustion engines or engines found in cars and aircraft.

In this article, we’ll discuss the three major types of fuel injection systems, the components of the system, and the history of the design. We’ll also highlight some common issues and how to spot them in your vehicle.


The task of all fuel injection systems is to supply fuel to the combustion process. The system helps to optimize power, efficiency, reliability, operation and, cost. With a fully functional fuel injection system, your vehicle will have a smoother throttle response, a more reliable adjustment to changes in temperature and pressure, fewer maintenance needs and better efficiency of fuel.

So, why do we need this system in our cars? Essentially, fuel injection systems allow the combustion (or burning) process to occur by combining air and fuel. This combustion of fuel occurs within the engine, creates energy and makes the car go. It goes without saying that without this process, your car would be pretty useless.


In the early days of automotive engineering, fuel and air were mixed by carburetors. These days, most vehicles use fuel injection systems, but carburetors can still be found in small engines.

The first fuel injector device was designed by Herbert Akroyd Stuart in the late 1890s. He used what was known as a jerk pump to meter out oil to an injector at high pressure. By the 1920s, the fuel injection system was commonly found in most commercially sold Diesel engines.

Another type of fuel injector, known as the indirect gasoline injection system, was developed by French engineer Leon Levasseur in1902. This system was used first in aircraft, before making its way into vehicle engines in the 1920s.

Direct fuel injection was used in vehicles and aircraft during the Second World War. Rolls-Royce and other well-known manufacturers implemented this system in their vehicles.

The electronic injection system came into prominence in the 1940s, with the tests of Alfa Romeo, who designed a circulating fuel pump system that used six electric injectors and a semi-high-pressure design.

Direct vs indirect fuel injection

Petrol fuel injection is always an indirect system. Petrol is injected into the inlet port instead of being injected straight into the combustion chambers. Indirect injection allows the fuel to mix with air before entering the chamber.

With direct injection, most commonly used in Diesel engines, diesel is fed into a cylinder that is filled with compressed air rather than mixing with air before entering the chamber.

The three main types of fuel injection

These are the three main types of injection systems that you’ll find in most vehicles.

1. Diesel fuel injection

While a vast majority of Diesel engines use a direct system, others use an indirect system. Indirect diesel injection requires the diesel to be injected into a pre-combustion chamber, before passing through a small passage on its way to the cylinder head. Within the cylinder, the air is drawn in, then heated and compressed. This atomizes the fuel which then self-ignites.

2. Basic fuel injection

Modern petrol systems all use indirect injection. The pressurized fuel is pumped from the fuel tank to the engine, where it’s distributed to a series of cylinders. Fuel is then sent to either the inlet manifold or the inlet port by the injector. The injector system is similar to a hose or spray bottle, with fuel being ejected in a misty form. As air passes through the inlet, it mixes with the fuel before the combined fuel and air move to the combustion chamber.

Fuel injectors must be fitted so that the fuel is sprayed in the direction of the inlet valve. Depending on what kind of injection system you have, you will need one of two types of injector.

The continuous injection system sprays fuel into the inlet port, you guessed it, continuously. While the engine is running, there will be a constant spray of fuel. The injector in this system doesn’t control the flow of the fuel and the flow is consistent. Its only job is to change the fuel’s consistency into a mist.

The timed or pulsed injection system delivers fuel in short, sharp bursts. These bursts can be controlled mechanically or electronically. These days, because of the inconsistency and fallibility of the mechanical injectors, EFi, or electronic fuel injection, has largely taken over, leading to an increase in reliability and a decrease in cost.

3. Mechanical fuel injection

This type of fuel injection is no longer common in modern cars. It was used for sports cars in the 1960s and ’70s.

In the mechanical system, you’ll find a high-pressure electric fuel pump near the fuel tank that pumps fuel to a fuel accumulator. This ensures that the fuel supply stays consistent and smooths over the pulses of fuel from the pump, keeping the supply steady. The fuel then passes through a filter before entering the fuel distributor., where it is sent to the cylinders.

The fuel amount is metered by a flap valve in the engine’s air tank which moves according to airflow. When the throttle is opened, airflow is increased, and more fuel is allowed into the cylinders.

Main components of the system

To understand how the system works, it’s important to get a grasp of how it’s built. Within the system, you’ll find the following parts:

  1. Fuel tank
  2. Fuel feed pump
  3. Injection pump
  4. Governors
  5. Fuel injector
  6. Nozzle

The fuel tank holds a reservoir of fuel and maintains this fuel at a steady temperature.

The fuel feed pump sends fuel from the fuel tank to the fuel injection pump.

The injection pump sends the correct amount of fuel to the injector at high pressure and the right time.

Governors are in place in some systems to regulate the fuel quantity when the engine is running at a high speed.

Fuel injectors allow for quick combustion. The injector atomizes the fuel into a mist which aids in the mixing process. It sprays droplets of fuel into the cylinder.

The nozzle is a component of the injector. Its job is to atomize the fuel.

Common Issues with fuel injection systems

Over time, or with poor maintenance, the fuel injection system can become damaged and faulty. You must take your car to a mechanic for frequent servicing to avoid any of these issues. Once the system does develop an issue, it will only get worse, and you risk damaging the parts even more.

1. Clogged injector

When an injector becomes clogged, petrol can’t make its way to the intake manifold. This can occur over time from a build-up of rust. It can occur if you happen to leave your car in idle mode or if you haven’t had the car serviced in a while.

2. Dirt build-up in the system

Injectors can leave behind a residue. Because of the high pressure and heat within the system, this can burn and begin to hinder the effectiveness of the system. It will result in a weak spray and an uneven pulse pattern.

3. The injector is stuck shut

If your fuel injector is unable to open, it won’t be able to send fuel through the nozzle. This can occur from rust damage or faulty windings and springs.

4. A leak in the system

This can occur over time from use. A leak will eventually lead to high fuel consumption, hard starting and general poor performance of your vehicle.

Signs you may need your fuel injection system serviced

If you notice any of these signs, it’s probably time you had a mechanic take a look at your fuel injection system.

1. Engine is misfiring

When the fuel supply is too low, your engine may misfire. This could be a sign of a clog, dirt build-up or a stuck injector.

2. Uneven engine power

If your engine is revving, this might be a sign of a dirty fuel injector causing an unsteady supply of fuel to the engine.

3. Wasting fuel

If you seem to be going through petrol too quickly, this is likely a signal of a leak in the system.

4. Smell

A strong smell of petrol occurs when fuel is getting into parts of the system where it doesn’t belong. The smell of fuel is also a tell-tale sign of a leak or of an injector that is stuck in an open position.

Final Thoughts

We hope this guide to fuel injection systems has given you a better grasp of how the engine of your car works. The fuel injection system permits the fuel and air to mix at the perfect ratio thus allowing combustion within the engine.

If you notice any of the engine issues we’ve discussed above, be sure to visit a mechanical engineer who can assess the system and ensure it’s in good health.