Fact Checked

What Is Electronic Fuel Injection (EFI)?

Dan Blacharski
Dan Blacharski

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 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.

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

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.

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.

Are EFIs bad for the environment?

Electronic fuel injection, or EFI, is not only not bad for the environment, but it's the best answer engineers can come up with for delivering fuel to the engine of a vehicle that best ensures a clean-burning, less volatile exhaust. EFI became the standard fuel system on all gasoline automobiles manufactured since at least the late 1980s. Some older cars still seen on the road today might have the letters MPFI (multi-port fuel injection) or SMPFI (sequential multi-port fuel injection) written as badges on the vehicle. This is from way back when the technology was still new and innovative.

Before EFIs and onboard computers, automobiles utilized a widely known gadget for properly metering fuel and air to be fed into the engine. This gadget is the carburetor. A carburetor is a fully mechanical device that solves the issue of fuel delivery for spark-ignition engines. While carburetors have been mostly phased out of on-the-road automobiles since the 1980s, other machinery such as lawnmowers, farm equipment and some industrial machinery still utilize carburetors even in their latest engine models.

Every car manufacturer in the world has adopted EFI as a standard in fuel delivery for gasoline cars. Direct injection for gasoline automobiles is the next evolution of the EFI system, but this is still a relatively new technology. Hyundai and Kia found out the hard way that switching from port fuel injection to directly injecting the fuel into the combustion chamber came with a laundry list of problems. The main issue is that port injection incidentally cleans the tops of the valves and the intake manifold as gasoline gets injected into the engine. Direct injection reroutes fuel around those parts, leaving them to gather crusty carbon buildups that have led to many vehicles failing prematurely. Toyota recently began manufacturing vehicles with both port injection and direct injection on the same engine to receive the benefits of both technologies.

Switching from carburetors to EFIs on all automobiles was a welcomed switch by drivers, vehicle manufacturers and repair mechanics everywhere. Carburetors were very finicky, often causing poor starting conditions for cars and even "flooding" the engine when it didn't work properly. Small passageways in the carburetor's frame can easily get clogged by gasoline sitting too long. Even on new engines made for lawnmowers and other outdoor power equipment, carburetors often are the most problematic system on the engine. The advantages to EFI are many:

Advantages of Electronic Fuel Injection

  • Easier vehicle starting
  • Cleaner, fuller burning combustions
  • Awareness of efficiency in real-time
  • No clogging or flooding
  • Better for the environment
  • Faster throttle response
  • Safer driving characteristics
  • Better fuel mileage
  • Lasts for the life of the vehicle

Do Electric Cars Use Electronic Fuel Injection?

Fully electric vehicles do not use electronic fuel injection. EFI is a system of fuel delivery for internal combustion engines only. Hybrid vehicles do have internal combustion engines that use EFI for their fuel delivery just like any other regular automobile in addition to using batteries and electric motors to supplement the vehicle's drivetrain, but fully-electric vehicles, such as a Tesla, certainly don't have EFI or any fuel delivery system for that matter.

EVs use only electricity to operate the electric motors that propel the vehicle down the road. There is no internal combustion engine on an EV, therefore there is no fuel system involved at all. EVs need to have their batteries charged by either a charging station or a charging hookup at home. An EV gets its power from the stored electricity available in the massive batteries. Those batteries, along with a power inverter and other computerized systems control the electric current flow from the batteries through the power inverter and finally to the motors that spin the wheels.

What Happens When Electronic Fuel Injection Malfunctions?

EFI is a complicated system involving a closed feedback loop. If any sensor of the multi-part system fails, the EFI may not receive the correct data from the engine computer and could send incorrectly measured amounts of fuel to the engine. On vehicles manufactured after about 1988, this sort of EFI system failure should cause the check engine light to illuminate on the dashboard. Additionally, the vehicle may misfire and run poorly, but it should still be able to drive. The vehicle should be brought to a mechanic immediately.

A warning light should indicate to the driver that a code-scanning device should be hooked to the dashboard's OBD2 port by a technician to better understand the particular issue. A mechanic will know if the trouble codes given by the car's computer are related to the fuel system or not.

Some states require emissions checks for vehicles to remain road-legal. A vehicle with EFI issues that causes the check engine light to illuminate will typically cause the vehicle to fail inspection. Not only is this malfunction bad for the car's engine, but it's especially bad for the environment when improperly combusted exhaust enters the atmosphere.

You might also Like

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.
      By: nui7711
      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.
      By: Svjatoslav Tokarev
      Fuel injection pumps take on a role similar to that of a carburetor.