Understanding Fuel System Parts, Types, and Functions

The fuel system is an essential system that helps in the combustion process in internal combustion engines. They help in transporting fuel to the combustion chamber to start the car. Here’s how it happens.

The fuel mixes with air before getting into the combustion chamber. The fuel travels through the intake valves, the pistons compress the fuel-air mixture, and the spark plugs ignite it to form an explosion. The explosion rotates the crankshaft, which then starts the car. But how does the fuel gets into the combustion chamber?

When you fuel your car at a gas station, the fuel enters the gas tank. Some system components transport the gas to the engine where it is needed. These components that house and supply the gas to the engine are the fuel system parts.

This article will explain car fuel system parts and how they work. But first, let’s look at the types of fuel systems.

fuel system parts and function

Types of fuel Systems

It is worth noting that diesel fuel systems and gasoline engine fuel systems are two different systems. However, we’ll try to explain fuel systems based on injection and mechanism.

Based on injection types

In injection types of fuel systems, we have direct and indirect fuel systems. Both gasoline and diesel-powered engines have these two types of fuel systems.

Direct injection fuel system

Direct injection (DI) is a fuel system that allows the fuel injectors to spray fuel directly into the combustion chamber from the top of the engine. A petrol direct injection (PDI), commonly referred to as gasoline direct injection (GDI), is a mixture formation for gasoline-powered engines.

The direct injection system is common with petrol engines. However, the system was firstly adopted by diesel engines. Here, the injectors supply the fuel directly to the combustion chambers from the top of the engine. As the fuel enters the engine, the air temperature inside the chambers rises to 400 degrees Celsius. As a result, ignition takes place immediately.

Indirect injection fuel system

As the name suggests, an indirect injection is a type of fuel system where fuel is not injected directly into the combustion chamber. In this fuel system, the injectors do not spray gasoline or diesel directly into the combustion chambers. Instead, it sprays the fuel into pre-combustion chambers in the head cylinder.

Direct injections help to achieve higher engine speeds in diesel engines. However, some auto manufacturers now have dual injection system that comprises both direct and indirect fuel injection functions.

Based on fuel injection mechanisms

Another way of looking at the fuel system is based on injection mechanisms. So in this category, we have three types of fuel systems.

Rotary fuel system

The rotary pump type works with a plunger. The plungers can suppress all the rotary pumps connected to the injectors. This fuel system (injector) has a simple design with fewer moving components. As a result, it doesn’t occupy much space in the engine bay.

However, the rotary fuel system has a weak injection pressure, making it less suitable for big diesel engines. Kindly, note that rotary fuel systems are found only on diesel engines.

Individual fuel system

As the name suggests, this fuel system has an inline injection pump with individual plungers. Here, the inline injection pump will have six plungers if the engine has six cylinders. Unlike the rotary fuel system, the individual fuel system has many moving components, making it suitable for big vehicles.

Common rail fuel system

In this type of fuel system, the injector pump is electronically controlled. Common rail fuel system differs from rotary and individual fuel systems. It uses a vane-type injector pump that supplies sustainable fuel to the combustion chambers.

The pump supplies high-pressured fuel into fuel rails, which carry the fuel to the corresponding injectors. The pressure inside the fuel pump is the same as the one on the fuel rails.

We’ve seen different fuel system types and how they work. Now, let’s look at fuel system parts and functions.

Fuel system parts name and descriptions

This section will teach you the fuel system parts and their function. This will help you know where to check when servicing the fuel system components in your car. If any of these components malfunctions or wear out, it’ll cause engine malfunctions.

Fuel tank

As the name implies, this is the tank that houses the fuel in your vehicle. The fuel stays inside the tank when you pump gas into your car from a gas station pump. The fuel remains inside the gas tank, and other system components transport it into the combustion chamber. The fuel tank also houses in-tank fuel pumps, fuel filters, floats, and fuel level gauge-sending units.

Fuel filters

The fuel system has to filter the gas before sending it to your engine for a smooth and seamless operation. Here’s where the fuel filter comes into play. It restrains dirt from entering the engine. This component is placed inside the gas tank or along the fuel lines before the fuel injectors.

However, some vehicles have two fuel filters – one inside the gas tank and the other outside the gas tank. The one inside the gas tank filters the fuel before entering the fuel pump, while the one outside the tank re-filters the gas before entering the fuel injectors.

Fuel pump

The fuel pump is responsible for transporting gas from the fuel tank. It is usually inside the gas tank. However, in old-model cars, the fuel pump is located outside the gas tank – usually between the gas tank and the fuel rails.

The fuel pump plays a critical role in starting a vehicle because every internal combustion engine-powered vehicle needs fuel to start. Therefore, fuel pump turns on the moment you start the car, and it stays on as long as the engine is running. This, however, subjects the fuel pump to fail; once the pump fails completely, the vehicle will not start until you replace it.

Fuel injectors

Like the fuel pumps, the fuel injectors transport the fuel into the combustion chambers. Electronic car sensors or computers usually control the injectors. In modern cars, the computers signal the injectors to spray more fuel when the driver steps on the gas pedal.

As soon as the driver releases the gas pedal, the fuel entering the combustion chamber is reduced, invariably reducing the engine speed.

Fuel lines

These are lines through which the fuel pump transports the fuels to the injectors. The fuel lines connect different fuel system components.


The carburetors are responsible for mixing fuel and air before sending the mixture into the combustion chambers. However, carburetors are seen only on older vehicles. Auto manufacturers equip newer cars with fuel injectors in place of carburetors.

Gas cap

The gas cap is the place you remove when filling fuel in a gas station. Of course, this is self-explanatory. It seals the fuel fill hose and prevents fuel from spilling from the car. It also ensures that the fuel system stays pressurized.

Fuel fill hose

A fuel fill hose is a metal or rubber hose that connects the gas cap to the gas tank. Its primary function is to direct gas to the fuel pump when refueling the vehicle.

Fuel gauge

A fuel gauge is a display unit that projects gas levels on the dashboard. This helps the driver to keep tabs on the gas level in the fuel tank. This, however, warns drivers when running out of gas.

Fuel sending gauge

This is a fuel system component mounted inside the gas tank. It works in unison with the fuel gauge to display the fuel level on the dashboard.

Fuel pressure regulator

The fuel pressure regulator system regulates the fuel pressures in fuel injection systems. Carbureted fuel systems do not have a fuel pressure regulator. Hence, this component is only seen in injection systems.


Q: What are the 4 parts of the fuel delivery system?

The fuel systems consist of several individual components that work in unison. However, the four parts of the fuel delivery system are the injectors, the fuel pumps, the fuel lines, and the fuel filters.

The fuel pump transports the fuel from the gas tank to the fuel injectors through the fuel lines. The fuel injectors collect the fuel and send it into the combustion chamber through individual cylinders. On the other hand, the fuel filters restraints dirt from entering the injectors.

Q: What is a 3-part fuel system service?

A 3-part fuel system service is a kit formulated to clean air and fuel lines and components, including intake valves, fuel injectors, throttle ports, plates, and combustion chambers. Since deposits in any of these areas disrupt proper engine performance and a 3-part fuel system service helps to clean the dirt, it is okay to say that a 3-part fuel system service improves engine performance.

Q: What are the 5 components of a diesel fuel system?

Both diesel and gasoline fuel systems consist of several system components. In diesel fuel systems, the five main components are the gas tank, gas filters, fuel transfer pumps, injector pumps, and gas nozzles.

As reiterated above, the gas tank stores the diesel in the car. The fuel transfer pumps draw the fuel out of the gas tank, and the gas filter filters the diesel before getting to the injector pump. From there, the injector pump sends the diesel to individual injection nozzles, which then transport the diesel to the combustion chambers.

Q: What is the most frequent failing component of a fuel system?

All fuel systems will last long with the correct fuel and quality system components. Above all, the primary cause of fuel system failure is dirt and contamination. So, since the fuel filter does the filtration work, it becomes a weak component in the fuel system. As the filter prevents dirt from entering the injectors, it becomes clogged over time.

However, you don’t necessarily have to replace clogged fuel filters. It may require cleaning.

Q: Do fuel systems need to be cleaned?

Just like the cooling system and the engine oil need cleaning, the fuel systems needs periodic cleaning. Experts recommend checking and cleaning your fuel injectors every 12,000 miles or every year. However, you need to check and clean the outside fuel filter whenever you notice high gas mileage, stalling, stuttering, or a misfiring engine.

Final Words

All fuel system parts are essential components that play a critical role in the overall engine operation. If some of these components malfunction, the engine will lose power, and the vehicle will not start if they fail completely.

For example, if one or two fuel injectors stop working, the engine will stutter, stall, and misfire. Likewise, if the fuel pump fails completely, the car won’t start. Therefore, you should ensure that all fass and ECI fuel system parts stay in good condition for optimal engine operation.


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