How Does Your Car’s Fuel System Work?

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fuel system

Carburetors were used more than 100 years ago until the 90s when they were almost completely replaced by the electronic fuel injection system.

Despite being more complex, a fuel injection system allows a car to be faster and consume less fuel because it can better manage the amount of fuel going into the combustion chamber.

The fuel system plays a vital role in the operation of your vehicle. If you want to get the most out of your vehicle, you’ll need to take care of its components, however, the definition of the fuel system in an internal combustion engine has changed over the last century. 

This article explains how your car’s fuel system works.

How Does a Car Fuel System Work?

Many things have to work together for a properly working fuel system. In the fuel tank, air and vapors enter from its vent. The fuel needs to be forced out of the tank, through the filter, and into the engine. A big enough pump (usually electric) forces this process along.

The fuel pump is usually mounted inside the gas tank because there’s no good place to put it outside without it getting in the way or being too susceptible to damage or weather conditions.

The fuel pump is usually positive displacement, meaning that the pump creates a vacuum, and gas is forced into this partial vacuum created by the movement of a plunger driven by an electric motor.

The fuel will go through the filter, where dirt and other particles are removed (this isn’t always done). From here, it goes to the carburetor or fuel injectors. In older cars, this is where a lot of dirt and gunk from inside the gas tank ends up.

Once the gas leaves the carburetor or fuel injectors, it’s now under pressure and gets pushed into the engine. The carburetor has a throttle plate that controls how much gas can be injected, so you open this plate up more if you need to increase power.

Some cars have a carburetor and then a fuel injection system. Some cars have only fuel injection. There are throttle body fuel injection systems, port fuel injection systems, and even some computer-controlled multiple-point fuel injection systems!

That’s the basic idea, though. The gas is put under pressure by the electric fuel pump, it is mixed with air by the carburetor or fuel injectors, then forced into the engine.

Fuel System Components

Following are the main parts of a fuel system in internal combustion engines:

  1. Fuel Tank
  2. Fuel Pressure Regulator
  3. Fuel Filter
  4. Fuel Lines
  5. Fuel Pumps
  6. Fuel Rail Pressure Sensor
  7. Fuel Injector
  8. Fuel Gauges
  9. Fuel Carburetor
  10. Fuel Pump Relay

Let us explain the purpose, working, and construction of each of these components one by one.

1. Fuel Tank

Fuel tanks in cars serve the purpose of storing gasoline. The gas tank is a flexible container made of rubberized fabric in many cases. In older cars, these were often strengthened by metal sheets, or in modern cars with higher safety requirements have them completely made from steel.

Modern cars usually have a gas tank that is located between the rear axle and front of the engine. The distance to the engine varies with different models.

2. Fuel Pressure Regulator

Fuel Pressure Regulators keep a check on fuel pressure inside the delivery pipe of the fuel pump just before it reaches engine cylinders. The regulator maintains a pressure difference of 1-2 kgf/cm² (kg per square cm) across the delivery pipe.

On the other hand, the fuel tank is pressurized at 20-30 kgf/cm². This pressure difference triggers fuel flow from the tank to the pump and then to the engine. In the case of mechanical fuel pumps, the fuel pressure regulator is not required.

3. Fuel Filter

The main job of a fuel filter is to clean the dirt and rust from fuel that is going to be supplied to the combustion chamber. Due to this cleaning process, there are chances that some amount of fuel might get wasted.

For this very reason, it is necessary for one to replace their fuel filter every 10,000 miles of driving or roughly after two years. If the fuel filter of a car is clogged up, it will shut down the fuel supply to the engine resulting in the car’s sudden stopping or stalling.

4. Fuel Lines

In a vehicle fuel system, the fuel lines are usually hoses that carry motor fuel from the fuel tank to an inlet of the carburetor or an electronic injection pump.

The flexibility and resistance to damage provided by using rubber for the lines allow them to be routed in areas that other, more rigid materials could not allow.

5. Fuel Pump

The fuel pump is an important component of a car’s fuel system. In simple words, it is a pump that helps in delivering fuel from the tank to the engine. It mainly comprises of a plunger and a gas spring that pushes the fuel out through the delivery pipe to the injection system or carburetor.

A car’s electric pump is attached to its tank. The only link between the two is a rubber hose which is connected to the fuel pump’s input port. The fuel pump output is connected to the car’s engine through a rubber hose again.

6. Fuel Rail Pressure Sensor

The function of the fuel rail pressure sensor is to monitor the pressure in the rail to ensure the correct performance for the fuel injection system. It is usually located at the tip of the fuel injector.

The fuel injection system uses high-pressure fuel to operate and relies on fuel rail pressure to control the timing and quantity of the injection.

7. Fuel Injectors

Fuel injectors are responsible for directly injecting fuel into the engine. They use a very small electric current to open and close a special valve that allows gas to pass from a fuel line into an engine cylinder. There is also a coil around the injector that controls its movements.

Fuel Injectors are divided into two categories: electronic or mechanical. Mechanical systems use a mechanical fuel pump and an electric, hydraulic or cable-driven throttle. Electronic systems use an electric fuel pump and an electric motor to open the throttle valve.

8. Fuel Gauges

Fuel gauges serve the purpose of letting drivers know when to refuel to keep their gas tanks full. Usually, when the fuel level drops below a certain point, the ‘Low Fuel’ light will turn on.

While this approach does its job of reminding drivers that they need to stop and refuel their vehicles at some point in time, it fails to consider alternative fueling methods.

9. Fuel Carburetor

The job of a fuel carburetor is to mix liquid fuel with air to form a combustible mixture. The carburetor has a closed chamber that is open at the top, allowing for maximum airflow and the free flow of liquid gasoline through the walls.

As the throttle valve is opened, airflow through the carburetor increases, which causes the pressure inside of the chamber to drop. This creates a partial vacuum that draws gasoline from one of two or three different fuel passages, each with its own jet needle.

The fuel must be atomized before it can burn in the fuel system. Fuel injection and carburetors use a device called a Venturi to do this. A Venturi is basically a constriction in the fuel line that speeds up the flow of fuel, which causes it to “breath” or break into small droplets.

10. Fuel Pump Relay

Fuel Pump Relay is a safety device that protects the car’s fuel pump, i.e., automatically energizes the pump during crank if the car’s ignition is on (even when the engine is not running). When the engine starts, it deactivates the fuel pump relay and vice versa.

What are the Two Types of Fuel System?

There are two types of fuel systems, and both work differently.

Carburetor system

This is the most common fuel system, which is still in use in many cars with an internal combustion engine. In this, air and gasoline mixture is supplied to the engine with the help of a small rubber tube fitted on a carburetor which mixes air with gasoline when it flows through small jets present in the carburetor.

Fuel injection system

This type of system is also known as a petrol injection system due to its working on petrol/gasoline. It is an advanced version of the conventional fuel system, which works with the help of a high-pressure pump and injects gasoline into the combustion chamber at very high pressure, supplied through a high-pressure pipe.

A high-pressure pump is used to pressurize gasoline from the tank, so there is no need for a rubber tube as in a carburetor system. Such injection systems are known as multi-point fuel injection systems due to multiple injectors fitted for proper working.

There are mainly three types of fuel injection systems are used in cars today.

1. Port injection system: In this, fuel is injected directly into the intake ports of the combustion chamber where air enters for mixing with fuel for proper working.

2. Direct injection system: This is also known as petrol direct injection(PDI) or simply central high-pressure fuel pump (CHFP) system. In this, fuel is injected directly into the combustion chamber for proper mixing of air and gasoline before entering the cylinder.

3. Common rail injection system: This works with the help of a high-pressure pump fitted on it, which pressurizes fuel up to 2500 psi/172 bar at the time of injection.


The most important components of the fuel system include the fuel tank, the fuel pump (which is usually driven by the engine’s timing chain),  the lines and fittings,  and the filter.  Rubber deteriorates and can crack or split with time, allowing fuel to escape.

If any component of the fuel system in your car malfunctions, it can pose a serious threat to your safety. If any of the components of the fuel system are not working, you might have to face the following issues:

1. The car may run out of fuel, even if there is a full tank

2. The engine often misfires or starts running roughly from time to time

3. Poor gas mileage

4. You can see dark spots under the car after fueling up the car

5. Fuel smells inside the car

6. Bad gasoline smell, often described as ‘rotten egg’ smell

7. You can see puddles of gasoline under the car

8.  Malfunctioning fuel gauge and rough idling at stop signs and lights

9.  Engine is more challenging to start than usual, or you have trouble starting it altogether

There is a wide variety of issues that could be causing damage to your fuel system, but what you need to do is have a professional diagnose exactly what the source of the problem is.  

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