The fuel system in a vehicle consists of a few components that help transfer fuel from the tank to the engine for combustion. Since fuel delivery to the engine is essential for smooth driving, your fuel system must always be in efficient working condition. If there is a lapse in the system, you will feel a loss in power and performance.
Let’s take a look at the components in a fuel system in detail to get a better understanding of how the fuel system works and how each component plays a part in the fuel system.
What is a Fuel System?
The fuel system is made up of the fuel tank, pump, filter, and injectors or carburetor, and is responsible for delivering fuel to the engine as needed. Each component must perform flawlessly to achieve the expected vehicle performance and reliability.
The function of the fuel system is to store fuel and deliver it to the cylinder chamber where it can be mixed with air, vaporized, and burned to produce power. The fuel, which can be either gasoline or diesel, is stored in a fuel tank.
A fuel pump draws fuel from the tank through fuel lines and pumps it through a fuel filter to either a carburetor or fuel injector and then into the cylinder chamber for combustion.
Parts of a Fuel System in a Car
We will cover all the parts to make you feel safe with your choices and how to connect and make them work together the best way.
The fuel system looks like this:
1. Fuel tank/Fuel cell.
A fuel tank must hold the fuel safely. It is mounted low and in the middle of the car. There you have a protected place with a low center of gravity.
This can be used to advantage if the car is to be tuned. It is really only if the original tank is not permitted according to regulations or if it has to be moved for constructional reasons that it is replaced with a so-called fuel cell.
The original fuel tank usually has the fuel pump mounted in the tank in a so-called fuel pump hanger. This can be converted to external fuel pumps, but then connections for this must be created; these are usually prepared on an aftermarket fuel cell.
Other connections that are located on a fuel tank and fuel cell are venting, refueling, and sockets for fuel outlet/inlet. Inlet and outlet are located in the fuel pump hanger if the tank is equipped for internal fuel pumps.
2. Fuel filler.
The fuel filler is located well above the fuel level and is there for fuel refilling. When fuel is added, the air inside the tank needs to be evacuated. This is done through a tank ventilation hose. This hose is routed up to the fuel filler along with the fuel filler hose. This allows faster fueling.
The fuel filler has hose connections around 50mm. The extra tank ventilation used to be around 10mm. Both used to be hose connections, but other versions are used depending on the manufacturer.
3. Roll over valve (Tank breather)
The tank breather must be mounted so that the fuel tank does not contract (vacuum) when the fuel pump pumps out fuel. And so the tank does not swell when it is hot outside, and gases expand. These are just two examples where the tank breather equalizes the pressure in the fuel tank.
OEM call this the EVAP system. Then the gases are led back to the engine intake by means of an electronic valve. This is because the system must be closed.
Tank venting on an aftermarket fuel cell is usually called a roll-over valve. This is then the venting, but it only leads out the fuel vapors in the simplest way in the open air.
A roll-over valve also works exactly as the name suggests. If the car ends up upside down in an accident, the fuel does not escape because the rollover valve closes the outlet when turned upside down.
4. Fuel pump.
The fuel pump feeds fuel from the fuel tank to the engine. It can be mounted in a tank or externally outside the tank. This is due to the design of the pump. An external fuel pump has threads on the inlet and outlet. An internal pump has a hose connection on the outlet and a quick connection to the pre-filter (inlet).
A high-pressure pump for electronic injection works between about 2 and 9 bar, while a low-pressure pump for carburetors and TBI systems works up to about 1 bar.
GDI/FSI/Piezo injectors for direct injection have a mechanical fuel pump that sits on the engine and is driven by, for example, a camshaft. This type of mechanical fuel pump can deliver pressures of about 200-2000 bar and sometimes more.
5. Pre-filter.
When refueling, coarser dirt can enter the fuel tank. The pre-filter of the fuel pump prevents this from entering the system.
Originally, the pre-filter is often built into the fuel pump housing. In the aftermarket, the pre-filter is mounted directly on the in-tank fuel pump.
An external pump, on the other hand, has a thread on the inlet which means that the in-line pre-filter can be mounted in series. This is done by threading the filter directly on the fuel pump or using a hose and fittings to connect them.
100-150 microns are used as pre-filters.
6. Check valve.
Originally, the check valve prevents the fuel lines from being emptied. The fuel remains in the lines for a quick start.
Aftermarket check valves are not as good at maintaining the pressure afterwards, but they are made to flow better than the original check valves. When an engine is to be tuned, several fuel pumps can be used, and if they start in steps, check valves are needed so that the fuel does not slip back through the pumps that are off.
Original = better seal = less flow = keeps the pressure up longer than aftermarket check valves.
Aftermarket = better flow = less seal = does not keep the pressure up as long as an oem check valves.
7. Fuel pump hanger.
The fuel pump hanger is a unit located in the fuel tank so that a fuel pump can be mounted in the fuel tank. This is the same principle for both OEM fuel tanks and the aftermarket fuel cell.
Original fuel pump hangers can also function a bit like a catch tank as the return fuel from the engine is recirculated here. Depending on the model, fuel level meters and sometimes also the fuel pressure regulator can be mounted here.
Aftermarket fuel pump hangers can look different and often allow the installation of several fuel pumps. Some also have a built-in catch tank, tank vent, and fuel level sender.
Driving without a fuel pump hanger and instead using an external fuel pump is also common on rebuilt cars.
8. Catch tank.
An external fuel catch tank is not used standard (OEM). During heavy cornering/racing, the fuel in the fuel tank is pushed to the side, away from the fuel pump. In this way, the fuel supply to the engine disappears.
To counteract this, the fuel is instead pumped to a catch tank that is filled up. Then another fuel pump pumps fuel to the engine from the catch tank.
Now there is always fuel in the catch tank during heavy cornering.
The catch tank can also be built into the fuel tank. But the same principle with two fuel pumps applies when one has to fill the catch tank and the other supplies the engine with fuel.
Fuel pumps can be located internally or externally in the catch tank.
Fuel path to engine:
- Fuel tank> Catch tank> Engine.
- The fuel’s way back to the fuel tank:
- Engine> Catch tank> Fuel tank.
9. Fuel filter.
A fuel filter is located between the fuel pump and the fuel injector. This filter prevents dirt from reaching the fuel injector.
Original fuel filters are often replaced with an aftermarket fuel filter if a car is tuned more, as the flow will be higher.
The replaceable insert on an aftermarket fuel filter is made of a paper material or stainless steel. Stainless steel is preferable as they last better and filters dirt just as well down to 10 microns.
10-30 microns are used as high-pressure filters.
10. Fuel rail.
A Fuel rail distributes the fuel between the different injectors that are mounted. The original fuel rail is good enough for a lot of power.
The reason for this replacement is that connections are often odd, and an OEM fuel pressure regulator is mounted directly on it as a restriction. Instead of rebuilding originals, this is instead replaced by an aftermarket fuel rail.
The internal size of the aftermarket fuel rail is usually 16-20mm to be able to distribute a lot of fuel between injectors.
A model-adapted fuel rail has the right distance between the injector holes to fit the engine. It does not necessarily have to come with model-specific mounts. Check this before buying.
11. Fuel injectors.
Injectors are the part that finally injects fuel into the engine using the control system (ECU). This can also have a filter mounted on the top.
There are injectors for electronic injection (EFI) that are mounted on the intake before the valves. And there are injectors for GDI/FSI/Piezo (Direct Injection) that are mounted in the cylinder head, down in the combustion chamber.
When tuning an engine, more fuel is needed. Therefore, larger injectors are mounted.
Top feed injectors (EFI) are mounted between the intake manifold and the fuel rail. The length of the injector can vary, but the length used before is the one usually used again.
12. Fuel pressure regulator (FPR).
An EFI fuel system wants a certain pressure, e.g., 3 bar, to then increase the pressure linearly in parallel with the engine boost pressure. This is so that the fuel injector can supply enough fuel. A fuel pressure regulator takes care of adjusting this.
The original fuel pressure regulator is very precise for the standard working area. With a tuned engine that requires more fuel, the original fuel pressure regulator can probably not adjust this that well anymore.
Aftermarket fuel pressure regulator for EFi systems easily adjusts between 3-9 bar and sometimes more.
13. Y-cross/Split.
A Y-cross/X-cross/split is simply used to divide several hoses or pipes.
If several fuel pumps are used or if you have a V-engine, a y-cross can be used connect these into one system/fuel line.
Aftermarket fuel pump hangers and fuel pressure regulators may have this built in already. eg 2-3 inlets and 1 outlet.
14. Fittings and hose.
All components in a fuel system have a thread or hose connection. One for the inlet and one for the outlet at least. These fuel parts are connected with the help of a hose and fittings.
Standard applications of then use a plastic hose that is heat crimped on connections. This is a very compact solution, but nothing that can be done at home yourself. Therefore, AN fittings and hose are used. With the help of these, all parts are easily connected together.
Do you want to use AN6 lines, for example? Simply adapt the product’s input/output to AN6 using adapters.
If you want to use classic 8mm hose and hose clamp, this also works well. Simply adapt the product’s input/output to the 8mm hose connection using adapters.
All this is easily done at home with a wrench if you want, completely without any special tools
How A Car’s Fuel System Works?
Ideally, when your vehicle’s gas gauge gets down to a quarter tank, you pull into your favorite fueling station and fill up the tank. The gas station pump is where fuel begins its journey:
- From the pump to the tanks, the gas travels through the fuel pump. The pump sends fuel from the gas tank to the engine. Some vehicles are equipped with multiple gas tanks and even multiple fuel pumps. Multiple fuel pumps are ideal for ensuring the vehicle always has access to fuel, no matter the terrain that the vehicle is traveling on. For example, if a vehicle is making a sharp turn or traveling on a steep incline and gravity forces fuel away from one fuel pump, it guarantees that at least one of the pumps has access to fuel.
- The pump forces fuel through the fuel lines that deliver fuel from the tank to the engine for combustion. Fuel lines are made of durable metal and plastic materials, and though they are located in the undercarriage of the vehicle, and seemingly in a vulnerable position, they are placed in areas that cannot be damaged due to elements, road conditions, or exposure to heat from the engine’s exhaust or other components.
- The fuel filter is the next stop for gasoline before it reaches your engine. It is imperative that the fuel that enters the engine be uncontaminated and free from dirt or particulates. To prevent any debris from entering the engine, the fuel filter will aid in removing dirt or debris. A clogged or dirty fuel filter is unable to trap harmful particulates from entering your engine and can cause all sorts of damage. Newer vehicles may not have serviceable fuel filters, as they are located in the fuel tank. Replacing the filter requires replacing the entire setup.
- Once passed through the fuel filter, the fuel reaches the engine and is injected into the combustion chamber to create combustion utilizing fuel injectors.
Different Types of Fuel Injection Systems in Cars
Broadly speaking, there are 4 different types of fuel injection systems in cars
- Single-point or throttle body injection
- Port or multipoint fuel injection
- Sequential fuel injection
- Direct injection
1. Single-Point or Throttle-Body Injection
This is the most basic type of fuel injection system. Also called the Throttle-Body injection system, the single-point system replaced the carburetor with up to two fuel injectors in the throttle body. For the uninitiated, the throttle body acts as the starting point of the respiratory system of a car’s engine, as it’s at the start of the air intake manifold.
The single-point fuel injection system worked well as a replacement for rudimentary carburetors before multi-point fuel injection systems came into existence. While these were not as precise as the multi-point units, they did offer better efficiency than carburetors. Also, they required lower maintenance and were even easier to service.
2. Port or Multipoint Fuel Injection
A common type of fuel injection system these days is the Multipoint Fuel Injection System, which offers a separate injector nozzle for every cylinder. It’s placed on the outside of each intake port, and this is exactly why it’s also called a port injection system at times.
Having the fuel vapor near the intake port makes sure that it will be completely sucked into the cylinder and enhance combustion. The biggest advantage of the MPFI system is that it regulates fuel in a more efficient way than carburetors or single-point fuel injection. Also, this system mitigates the possibility of fuel condensation in the intake manifold.
3. Sequential Fuel Injection
A sequential fuel injection system is also known as a sequential port fuel injection system (SPFI) or even a timed injection system.
The biggest difference between multi-point fuel injection and sequential fuel injection is that in the former, all the injectors spray the fuel at the same time, which means the fuel often remains in a port for more than 150 milliseconds when the motor is idling.
While it might not sound like much time, it’s actually more than enough time to decrease efficiency. In a sequential fuel injection system, each nozzle sprays fuel independently.
Basically, they spray the fuel just before the intake valve opens, which means the fuel doesn’t have to hang around for long. As a result, the efficiency improves, and emissions decrease.
4. Direct Injection
Direction injection is easily the most advanced type of fuel injection system. In this system, fuel is directly sprayed into the combustion chambers after the valves. This system is mostly found in Diesel engines, but of late, it has also started making its way to mainstream petrol motors.
For example, the 1.0-liter turbo-petrol motor of the Hyundai Venue gets direct injection and is marketed as ‘GDI.’ In this arrangement, the regulation of fuel and the timing of spraying it is even better measured than in any other injection system.
What Is Included in a Car’s Fuel System Service?
Fuel is critical for vehicle operation. To avoid failure of fuel components, especially the fuel pump, it is important to maintain your fuel system. If any fuel components fail, your car will not run or will be difficult to run.
To avoid issues, never let the vehicle’s fuel level drop below a quarter of a tank, replace the fuel filter, and have fresh fuel system cleaner installed regularly.
Change your fuel filter every 60,000 miles and have a fuel system cleaning every 30,000 miles. This will minimize the likelihood of being stranded with bad fuel injectors, a dirty fuel filter, or a failed fuel pump.