Maintaining Your Vehicle
The Fuel System in Your Car

The Fuel System in Your Car: Common Malfunctions and Maintenance

Updated Jan. 2, 2021

Your vehicle’s fuel system is responsible for storing, filtering and supplying gasoline to the engine, where it can be ignited to create power. The main components in the fuel system are the gas tank, fuel lines, fuel pump, filters and fuel injectors. Together, they coordinate the delivery of clean fuel and air to the cylinders in the vehicle’s engine. If any one component in the fuel system stops working as well as it should, the entire fuel delivery process will be compromised. Like all other systems in your car, the fuel system requires regular maintenance to keep everything clean and running efficiently.

Fuel storage and delivery

In most passenger vehicles, the gas tank is situated close to the rear wheels. Fuel tank capacities vary from vehicle to vehicle. A typical small car can hold around 12 gallons of gasoline, while larger vehicles can usually take 15 or 16 gallons. Most modern vehicles are built with gas tanks made from high-density plastic, which is both structurally sound and resistant to wear. Steel or aluminum are also used to make gas tanks, though this is more common among older vehicles. Metal gas tanks are susceptible to rust, so it is useful to know if your car has one.

Attached to the gas tank is a fuel pump, which sucks gasoline out of the tank and draws it along the fuel lines to the engine. This important component is also responsible for keeping the fuel at a safe temperature and maintaining pressure throughout the fuel lines.

Air fuel mixture

As fuel cannot burn without oxygen, the gasoline must be combined with clean air before it is injected into the combustion chamber. The air-fuel mixture is precisely measured to achieve consistent combustion and maximize fuel efficiency. This process is either managed by a carburetor or fuel injectors, depending on the design of your vehicle’s fuel system.

Carburetors are less efficient and generally found in older vehicles. This tube-shaped component connects the fuel line with the engine cylinders. As gas travels along the fuel line, it passes through a narrowed section of pipe before entering the carburetor. This creates a low-pressure environment that causes air to be sucked into the carburetor through a valve in its side, where it combines with the fuel. This mixture is then sent to the engine cylinder for combustion.

Modern vehicles tend to have electronically controlled fuel injectors, which are far better at achieving the ideal air-fuel ratio. As gas is drawn from the fuel line, the fuel injector atomizes it and forces it through a needle-like nozzle at high pressure. As the fuel-air mixture can be measured precisely and consistently, fuel injectors allow for better fuel efficiency and help to maintain the health of the entire fuel system. Vehicles with fuel injectors tend to be more reliable and require less maintenance.

Whether your vehicle uses a carburetor or a fuel injector, the air-fuel mixture passes through an intake manifold to reach the cylinder’s intake valves. The intake manifold’s job is to feed the air-fuel combination into the cylinders, making sure that each cylinder receives precisely the same amount.

Fuel filtering

When exposed to high-pressure and heat, gasoline reacts to create microscopic carbon deposits. This can occur and cause a build-up of sediment anywhere in your vehicle’s engine and fuel system, though it is particularly problematic around narrow pipes and nozzles, which can easily become blocked. Impurities in gasoline can also contribute to fuel system blockages. Fortunately, fuel in the United States can only be sold if it meets a minimum standard for purity and has added chemicals to minimize carbon deposits. Though over time, a build-up of deposits can still occur and cause untold damage to your fuel system and engine.

The fuel system has filters along the fuel line and near the injection system, which are designed to remove impurities and carbon deposits from gasoline, to prevent blockages. These must be changed regularly, in accordance with the recommended frequency in your vehicle owner’s manual.

Air filtering

The air used in the air-fuel mixture which feeds your car’s engine is drawn from the environment outside the vehicle. As this air enters the engine compartment through a vent at the front of the hood, it will contain dust, dirt and other particles kicked up from the roadway. These impurities must be removed by the engine’s air filters before the air can be mixed with fuel. Like fuel filters, engine air filters must be replaced on a regular basis. Over time, they will become less efficient and may allow harmful particles to pass through into the engine.

Fuel leaks

While your vehicle’s fuel system is designed to be hard-wearing and secure, fuel leaks can occur if the system’s components are not properly maintained. As gasoline is incredibly flammable and gives off harmful gases, even minor leaks anywhere in the system are extremely dangerous. Your gas tank, fuel lines, fuel pump and fuel injector must receive regular servicing to prevent dangerous leaks. Make sure you secure the gas tank cap properly every time you refuel the vehicle, as loose caps can lead to fuel leaks.

Never drive a car that may have a fuel leak. If you smell gas in the passenger compartment after refilling the tank, get a mechanic to check the system for leaks immediately.

Common fuel system malfunctions

Your vehicle’s fuel system is designed to need very little maintenance beyond occasional cleans and filter changes, as recommended in the vehicle owner’s manual. However, problems with components in the fuel system can occur and if left unchecked, may develop into serious malfunctions that warrant expensive repairs. Here, we discuss three of the most common fuel system malfunctions and their early warning signs. If you think there may be a problem with your fuel system, get your vehicle checked out by a mechanic right away.

Dirty fuel filter

The filter’s job is to clean impurities and deposits from gasoline, as it is pumped from the storage tank to the engine. You should not have any problems with the fuel filter if you take care to replace it regularly. Over time, your fuel filters will become blocked with dirt and residue from the fuel. If this happens, the flow of gas along the fuel line and through the fuel injector or carburetor will be restricted. If the filter is not changed, eventually, the engine will not be able to start at all.

Fortunately, it will become apparent quite quickly if a dirty fuel filter is restricting the flow of gas into the engine. Insufficient fuel in the cylinders means less power for the vehicle. You may notice that the car has difficulty maintaining speed, or that applying pressure to the gas pedal causes jerky acceleration. Do not ignore these symptoms; they will escalate quickly if the fuel filter is not replaced.

Fuel pump malfunction

Driving with low fuel levels can cause the fuel pump to wear out prematurely if you make a habit of it. Fuel pump failures can be expensive, as the part cannot be serviced and must be completely replaced. If the pump ceases to work, no fuel will be able to reach the engine. This will likely result in the engine turning over but failing to start when you turn the key in the ignition.

The early warning signs of a fuel pump malfunction are similar to those of a dirty fuel filter. The vehicle may have difficulty accelerating, though this is more likely to occur at high speeds. You may also hear a loud ticking or a high-pitched whine coming from the engine while it idles. If left unaddressed, a faulty fuel pump could cause your engine to cut out while you are waiting at traffic lights or temporarily stopped in a line of traffic.

Fuel injector failure

Modern fuel injectors have extremely fine nozzles that can easily become clogged with impurities and carbon deposits. If this occurs, the engine may rev erratically while running at an idle. You may also notice inconsistent acceleration and an overall bumpier ride when traveling at high speeds. Increased fuel consumption is one of the earliest warning signs that your fuel injector is struggling. If you find yourself topping up the tank more frequently despite no increase in daily mileage, it may be time to get a fuel system health check. Fuel injectors can usually be serviced rather than totally replaced, providing you catch the problem early enough.

Fuel system maintenance

The filters and injectors are the fuel system components that require the most attention. The filters will need to be changed, and the fuel injectors cleaned, in accordance with the guidelines in the vehicle owner’s handbook. Keep in mind that the service frequency recommended in the owner’s manual is for general guidance only. If you spend a lot of time driving in built-up, inner-city areas, your fuel system is likely to accumulate more impurities and may need servicing more regularly. If most of your mileage is spent over long journeys on high-speed highways, you may be able to leave a longer period between fuel system services – though it is best not to take this chance. The earlier you see to any issues with your fuel system, the less it is likely to cost you in the long run.

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