What is a Fuel System?

Open the cap, insert the nozzle and begin fueling. Gassing up is the extent of what most drivers know about their fuel systems. They have no idea what happens after they fire up their engine and drive away – nor do they care. To prevent yourself from being one of those people, you need to know how your vehicle’s fuel system works.

Let’s start with the basics. Just what does your fuel system include?

  • Fuel tank: Most tanks are made of sheet steel that has been pressed into shape. This is where the fuel starts its journey through the system – no surprises here.
  • Fuel pump: The fuel pump is typically located in the tank of modern, fuel injected vehicles. The fuel pump does exactly what its name implies – it pumps fuel from the tank to the injectors. The pump must deliver fuel to the injectors under high pressure (typically 30 to 85 psi) so the injectors can spray fuel into the engine.
  • Fuel lines: Carries fuel from the tank to the injectors and back. Unless of course, your vehicle is a fancy new return-less style system, then there’s no return line.
  • Fuel filter: The fuel filter is designed to filter out all of the nasty stuff that may be trying to make its way from the bottom of the tank to the fuel injectors.
  • Fuel rail: The fuel rail houses the injectors and has an inlet connection that attaches from the fuel filter.
  • Fuel pressure regulator: In a traditional fuel system, the regulator controls the return of fuel to the tank in order to maintain pressure at the rail.
  • Fuel injectors: This is where the action takes place – the injectors are solenoid operated valves which deliver fuel to the engine in the form of an atomized spray.

So, those are the usual suspects in a modern, fuel injected engine. If you’re an old timer however, you will likely recall with fondness a time when carburetors ruled the land.

What happened to carburettors?

Carburetors are simple, mechanical creatures. Instead of using individually controlled fuel injectors, the carburetor mixes air and fuel together before metering it into the engine. First, air is pulled into the carburetor by engine vacuum. Then, fuel is siphoned from the carb’s fuel bowl and mixed with the incoming air. When the engine is at idle, fuel enters the engine through small ports located above the throttle plate. When you mash the throttle, fuel flows through the main metering jets to the venturi. The air/fuel mixture then continues its journey through the intake manifold and into the cylinders where it will be burned to make power.

To summarize, the fundamental difference between carburetors and fuel injection – aside from the fact that the former is much simpler than the latter – is that carburetors use vacuum and a pressure drop in the venture to siphon fuel from the bowl into the engine, whereas fuel injection uses pressure to spray fuel directly into the engine. Generally, fuel injection provides greater fuel economy, engine performance and emissions control. In other words, the good ol’ days of the carburetor weren’t so great after all.

Over the years, fuel systems progressed from carburetors, to throttle body injection (an early, crude form of fuel injection), to multiport injection, and now finally, we are witnessing the industry wide adoption of direct injection.

A fuel injector might not look like much, but there’s a lot going on inside that tiny package. When a solenoid inside the injector is turned on, it lifts a valve off its seat and the injector sprays fuel. The solenoid is turned on an off by the control computer grounding and un-grounding the injector circuit. The longer the computer grounds the injector, the longer the injector sprays.

In modern applications, fuel injectors live in either a multiport or direction injection system. Both multiport and direction injection use a separate fuel injector for each cylinder. The difference is multiport injection sprays the fuel into the cylinder head intake port, whereas direction injection sprays fuel right into the combustion chamber. The advantage of direction injection is that it provides a significant improvement in fuel economy and power. And who doesn’t want that?

Today’s modern fuel injection systems are definitely more complex than their carbureted ancestors, but the benefits make it worthwhile. Now that you have a basic understanding of how fuel injection works, you can better appreciate the technology that blends power, convenience and economy. After all, would you really want to go back to your cabureated1972 Dodge that got 8 mpg?

If you want to improve your fuel efficiency and improve your car’s performance a good fuel system cleaner will help.  Check out our fuel system cleaner review for some of the most popular products.