How a Car’s Fuel System Works

In the past decade, the demand for more powerful engines AND better fuel economy at the same time has led to massive advancements in ignition, timing, and fuel systems. Let’s take a look at how a common fuel system works, and what’s changed over the last 50 years.

How Fuel Moves Through a Car

1. It Starts with the Fuel Pump

If you want to be technical, it starts at the tank when you remove the gas cap and pump fuel in. From here, both gasoline and diesel fuel are picked up by the fuel pump, where the real action begins.

The vast majority of vehicles today have a fuel pump that resides in the fuel tank itself. If it doesn’t, it’s located on the frame or subframe, which is far less common. On a standard electronic fuel injected vehicle, which still makes up a vast majority of vehicles on the road, this pump then provides the volume, and pressure of the fuel. Older, carbureted vehicles generally have a suction-style fuel pump that is mounted to the engine, and draws the fuel out of the tank, into the pump, and pressurizes it on its way to the carburetor.

The newest technology for gasoline engines is direct injection, which requires in most cases 2 fuel pumps – a “lift” or “transfer” pump which pumps fuel up and out of the fuel tank, and then a pressure pump, usually mounted on the frame or subframe of the vehicle, which then provides fuel to the injectors at high pressure. This is very similar to how a Diesel engine works, where the lift pump in the tank supplies fuel usually to a mechanical, high pressure pump mounted on the engine.

2. It travels through Fuel Lines and Filters

If the fuel pump does what’s expected of it and draws the fuel from the tank, this fuel first has to travel through metal or plastic fuel lines, which run from the tank to the engine. The fuel filter then actively filters this fuel to remove micro-debris, whether it’s fasoline or diesel.

3. The Fuel Pressure Regulator

All fuel systems have an optimum pressure they have to run at. On older carbureted engines, this pressure is low – between 3-5PSI. On multi-port Electronic Fuel injection systems, it’s much higher – usually between 50-90PSI. Each system will have a regulator that takes the fuel pressure from the pump, and regulates it to the proper volume, and pressure. While fuel pressure regulators don’t commonly fail, they can, and when they do, issues with performance or no-start/no-run situations can happen. On most Diesel engines, the injection pump, or pressure pump, also controls the pressure.

4. Next Stop, the Engine

After the filter has removed any contaminants and the pressure regulated properly, it is time for the fuel to go to the engine where it can finally be of use. There are a few different ways the fuel can go into the engine. Which way your car does it is likely a matter of when your car was built.

  • Carburetors were the norm of getting fuel to the engine for half a century. The carb had a float that would raise and lower to allow gas to enter the engine at different rates, depending on how open the float was.
  • Fuel injectors handle supplying fuel to almost all modern engines. These devices can be either mechanical or electronic, whereas modern systems, either Direct-Injection or Multi-port/Sequential are all electronic. Electronic fuel injectors are controlled by the ECU, and can inject fuel with far greater precision than a purely mechanical carburetor because the ECU has total control.

Once the fuel is in the engine, it can be combusted and expelled through the vehicle’s exhaust system.

Learn more about your fuel system

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