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Summary
  • The fuel system includes various parts like the gas tank, fuel pump, fuel lines, fuel filter, and fuel injectors.
  • The fuel injection system replaced the carburetor, and it comes in mechanical and electronic types.
  • Keep the fuel system in good shape by regularly checking and replacing the fuel filter, cleaning the throttle body and fuel injection system, and keeping fuel levels above 25% percent of the fuel tank’s capacity.

Your vehicle’s fuel system is a modern marvel tucked neatly under the hood. It takes care of everything from pumping fuel down the lines to injecting it into your engine’s cylinders. Most modern vehicles use a fuel injection system. If you’ve ever wondered “How does gas work in a car?” you’ll find the answer in this article.

How Do Modern Fuel Systems Work?

The modern fuel system is a series of many different moving and static parts in your vehicle. These parts move fuel and transform it into a usable state for your engine.

Gas Tank

It all starts when you fill up your tank at the gas station. The tank is where your vehicle stores excess fuel before use. It’s typically made from corrosion-resistant steel or polyethylene plastic. All fuel tanks incorporate an inlet or filler tube for the fuel to enter the tank, a pressure-holding filler cap with relief features, and a fuel pump mounted in the tank.

Fuel Pump

Once there’s gas in the tank, the fuel pump takes over. Most vehicles use either an impeller or turbine pump driven by a small electric motor. The fuel pump pressurizes the fuel before it’s pushed through the lines and towards the engine. When the fuel is pressurized, it has a higher boiling point, which prevents vapor from forming and interrupting the fuel’s flow.

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Certain vehicles have multiple gas tanks and fuel pumps to ensure that the gas gets to the engine even when the vehicle is running on uneven or extreme terrain. Even if the fuel sloshes around, one of the pumps should be able to still maintain a steady flow of fuel in the system.

automotive fuel system and injectors
Fuel injection proved more efficient and accurate at tempering the air-fuel ratios in different vehicles, so carbureted vehicles were no longer produced by the 1980s.

Fuel Lines

Fuel lines are an important part of the fuel system and the next step for the gas after it’s dispensed by the fuel pump. The lines are made of different materials depending on what they’re being used for. Rigid lines are the parts fastened to the vehicle’s body, frame, or engine. These parts of the line are made of seamless steel or nylon-reinforced plastic tubing. On the other hand, the rubber hose parts of the line are made of synthetic rubber and are used where flexibility is needed.


The fuel lines need to be kept in good condition since they need to contain the pressurized gas of the fuel injection system as it’s being transferred. This pressure can reach up to 60 PSI for multiport fuel-injection systems.

Fuel Filter

It’s common for there to be impurities in fuel despite all the refining it’s put through. That’s why it’s essential for the fuel to pass through the fuel filter before it enters the engine. Depending on your vehicle, the fuel filter is either integrated into the fuel pump or separate and connected to the pump via the fuel lines.

In a lot of vehicles, there’s at least a strainer-type filter in the tank and another one between the tank and the engine. The fuel filter or strainer in the tank filters a lot less than the one upstream.

In a lot of vehicles, there is at least a strainer type filter in the tank and another one between the tank and the engine. The fuel filter or strainer in the tank filters a lot less than the one upstream.

Anthony Harlin, ASE Certified Master Automobile Technician

Fuel Injectors

Once the fuel passes through the fuel filter and the fuel lines, it goes on to the engine. In a modern vehicle, the fuel injectors handle this. A pipe called the fuel rail channels the pressurized fuel into the injectors. After that, the fuel injectors spray the fuel through a small nozzle into the engine’s intake valves. The nozzle atomizes the fuel into a fine mist that burns easily in the engine.

The Modern Fuel Injection System

The fuel injection system replaced the carburetor. Both are designed to control the amount of air and fuel in the engine to achieve a stable ratio as it runs. A carburetor allows the air flowing through its system to deliver fuel to the engine. It controls the air-fuel ratio using a venturi, which dispenses the fuel in proportion to the amount of air entering the intake. However, fuel injection proved more efficient and accurate at tempering the air-fuel ratios in different vehicles, and carbureted vehicles were no longer produced by the 1980s.

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There are two different types of fuel injection: mechanical fuel injection and electronic fuel injection.

Mechanical Fuel Injection

Mechanical fuel injection came first. This was the first version of fuel injection on the market, and in the late 1960s, it was the only choice for vehicle owners who wanted something other than a carburetor. Like a carburetor, a mechanical fuel injector measured and dispensed fuel to the engine. It used a complex camshaft that moved according to the vehicle’s revolutions per minute (RPM). Driven by centrifugal force, the camshaft also rotated along with a press on the gas pedal. The pump’s plungers would be rotated by a toothed rack controlled by a follower on the camshaft, which altered the amount of fuel the pump delivered to the engine. Other mechanical components would alter the follower’s path based on things like coolant temperature and barometric pressure.

Today, a vast majority of mechanical fuel injection systems are only used by drag racers. These systems require a lot of attention and maintenance, and most casual vehicle owners don’t require the increased performance this constant-flow system provides.

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Electronic Fuel Injection

Most modern cars today use electronic fuel injection. It’s run entirely by the powertrain control module (PCM). To start, the PCM takes readings from different sensors scattered throughout the system. These sensors include knock sensors, inlet air-temperature sensors, and oxygen sensors. Once the PCM knows the engine conditions, it’s able to calculate the exact amount of fuel to dispense to the engine to maintain the correct air-fuel ratio.

Recommended Maintenance

There’s no question that your vehicle’s fuel system is a modern marvel. However, even with an electronic fuel injection system under your hood, there are still a few things you should do for maintenance.

  • Check your fuel filter regularly and replace it annually or every 12,000 to 15,000 miles.
  • Hire a licensed mechanic to clean your vehicle’s throttle body and fuel injection system every 20,000 to 30,000 miles.
  • Try not to let your fuel level fall below 1/4th of a tank.
About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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