What Is Electronic Fuel Injection (EFI)? (with pictures)

Dan Blacharski
Dan Blacharski
Fuel injection systems supply fuel directly to the cylinders of a vehicle's engine.
Fuel injection systems supply fuel directly to the cylinders of a vehicle's engine.

Electronic fuel injection is a type of technology and mechanical structure that supplies fuel to an engine. These systems are most common in automobiles and trucks. All cars sold today in the United States are required to have electronic injection systems in large part because of these systems’ overall efficiency and reliability, and most new cars manufactured around the world rely on electronic models for similar reasons. The earliest cars used carburetors to transfer fuel between chambers. Carburetors are still very common in small appliances and machinery, but as cars became more advanced and complex it became harder and harder for carburetors to keep up. Electronic models use a series of circuits and pressure gauges to open and close fuel valves with precision and at high speeds. A series of sensors positioned throughout the engine helps keep the process running smoothly and can also be a quick means or identifying problems and needed repairs.

Engine Mechanics on a Basic Level

Fuel injection pumps take on a role similar to that of a carburetor.
Fuel injection pumps take on a role similar to that of a carburetor.

The engineering and science behind how engines work can be fairly complicated, but on a very basic level their main purpose is to take a fuel, usually petroleum gasoline or diesel, and convert it into energy that can be harnessed to produce motion. There are a number of steps in this process, but getting the fuel out of its tank and into the engine’s combustion chamber is one of the most critical. Electronic fuel injection (EFI) is the modern market standard, at least for cars. It’s a precise technology that is able to deliver just the right amount of fuel in response to driver command and engine needs.

Progressing Past the Carburetor Model

Though the vast majority of cars and trucks throughout the world today embrace an EFI model, earlier automobiles had carburetors, which were less efficient. Some other types of small engines, such as lawnmowers or rototillers, still use carburetors, as do many older cars still on the roads. These are more prone to failure and can be expensive to fix.

The first electronic injection systems were throttle body systems, or single point systems, and featured an electrically controlled fuel injector valve. Later, these were replaced by more efficient multi-port systems, which have a separate fuel injector for each cylinder. The latter design is better at metering out fuel accurately to each cylinder, and also provides for a faster response.

Focus on Efficiency

Although an electronic fuel injection system is much more complicated than a carburetor, it is also much more efficient. The injector is a type of valve that is controlled electronically, which opens and closes and supplies atomized fuel to the engine. It sprays fuel into the intake valves directly in the form of a fine mist. The injector opens and closes rapidly, and the pulse width, or the amount of time it stays open, determines how much fuel goes into the valve. Fuel is supplied to the injectors by a fuel rail.

Role of the Sensors

Several sensors are included as part of the system, mostly to ensure that the correct amount of fuel is delivered to the injectors and then to the intake valves. These sensors include an engine speed sensor, voltage sensor, coolant temperature sensor, throttle position sensor, oxygen sensor, and airflow sensor. In addition, a manifold absolute pressure sensor monitors the air pressure in the intake manifold to determine the amount of power being generated.

In a sequential fuel injection system, the injectors open one at a time, in conjunction with the opening of each cylinder. Some other injection systems may open all injectors simultaneously. The sequential option is advantageous because it allows for faster response when the driver makes a rapid change.

The entire injection system is controlled by an electronic control unit (ECU), which functions as a central exchange for information coming in from all the various sensors. The ECU uses this information to determine the length of pulse, spark advance, and other elements. The ECU has several safety features built in, including a fuel cut parameter and top speed parameter.

You might also Like

Readers Also Love

Discussion Comments


@anon31718- Electronic fuel injection systems control emissions by controlling combustion. All of the myriad sensors monitor the mix of fuel and air, the pressure of the incoming air, fuel pressure, exhaust composition, compression, and backpressure. All of these have an effect on the emissions produced by a vehicle.

For example, a car that has a bad airflow sensor might make the fuel air mix too rich. This rich mixture will create a dirty burn (incomplete combustion), that will eject black soot in the exhaust. This could also trigger a check engine light, and make it harder for the vehicle to pass inspections.

With a little care and regular maintenance, you will have very few problems with an electronic fuel injection system. Mechanical fuel injection may seem simpler, but it is actually harder to calibrate than an electronic system. Change your filters, clean your MAF, and periodically check your fuel system and your car will last a long time.


@anon23961- There are a number of components in an electronic fuel injected engine. An OBD-II scanning tool can be used to scan the electronic components of a vehicle, returning a code that can clue you into any problems. Other components can cause a multitude of problems depending on what the problem is. For example, clogged injectors can cause rough or slow acceleration. Problems with the various sensors can lead to imbalances in fuel to air mixture. A clogged fuel pump can cause fuel injection system pressure problems.

The fuel system is one of the central systems within a motor, and problems with the EFI can lead to a number of different problems with a number of different components. Honestly, I would take the vehicle to a trusted mechanic before making any purchase. Electronic fuel system problems can be tricky to diagnose, and repairs can be costly.


So are there any benefits to using an older style of fuel injector instead of an EFI system? It would seem to me that an EFI system might have more potential for things to go wrong with it, but I'm not really that car-savvy, so I could be totally wrong. Does anybody know?


How does the EFI engine control the emission?


Hi. How we can identify an EFI related problem in a pre-owned vehicle?


how does a 1994 mitsubishi glxi efi work?

Post your comments
Forgot password?
    • Fuel injection systems supply fuel directly to the cylinders of a vehicle's engine.
      Fuel injection systems supply fuel directly to the cylinders of a vehicle's engine.
    • Fuel injection pumps take on a role similar to that of a carburetor.
      Fuel injection pumps take on a role similar to that of a carburetor.