Electronic fuel injection System : Parts ,Types, Working , Advantages

EFI System – Electronic Fuel Injection System : 

In Electronic Fuel Injection System, carburetors were replaced with throttle body fuel injection systems, also known as single point or central fuel injection systems. That incorporated electrically controlled fuel-injector valves into the throttle body. Those were almost a bolt-in replacement for the carburetor, so the automakers didn’t have to make any drastic changes to their engine designs.

Difference Between Electronic Fuel Injection and Carbureted fuel system

Sr no.Electronic Fuel InjectionCarbureted fuel system
1.Uniform distribution of charge.Mal-distribution of charge.
2.Improvement in volumetric efficiency due to less resistance in the intake manifold.Due to resistance in the intake manifold, volumetric efficiency is lower
3.Accurate metering of chargeInaccurate metering of charge.
4.The formation of ice on the throttle plate is eliminated.Carburetor Icing may take place
5.Atomization of fuel is independent of cranking speed therefore cranking is easier.Fuel atomization depends upon the velocity of air in the venture.
6.Better atomization and vaporization will make the engine less knock prone.Less atomization and vaporization will make the engine more knock prone.
7.Less volatile fuel can be used.Fuel needs to be more volatile
8.Fuel being injected into or close to the cylinder.Fuel injection is take place inside the manifold.

Types Of Electronic Fuel injection System:

  • Single-Point or Throttle Body Injection
  • Port or Multi-Point Fuel Injection
  • Sequential Fuel Injection
  • Direct Injection

Single point injection System:


A type of electronic fuel injection system that uses a single injector or pair of injectors mounted in a centrally located throttle body. The throttle unit resembles a carburetor except that there is no fuel bowl float or metering jets. Fuel is sprayed directly into the throttle bore(s) by the injector(s).

With single-point injection it is possible to achieve a lambda regulated exhaust emission control using only a few components.


  • Inductive pickup – position of the crankshaft and speed of the engine;
  • Lambda probe;
  • Temperature sensors for cooling water system and air intake system; Throttle potentiometer;


  • Fuel injector; – The fuel injector acts as the fuel dispensing nozzle. It injects liquid fuel directly into the engine’s air stream. The injection is controlled by the ECU. It determines the amount of fuel to injected and in some system if the engine is cold, turns on an “extra” injector which only works while the system is cold. This injector only works for a short period of time determined by the ECU.
  • Throttle plate control- This is system is used to control the minimum airflow during idle speed. It actuates directly in to the Throttle plate, this is normally done by a small electric motor applied directly to the throttle plate.

Electronic Fuel Injector (Unit Injector):

  • A vacuum-powered fuel pressure regulator at the end of the fuel rail ensures that the fuel pressure in the rail remains constant relative to the intake pressure. For a gasoline engine, fuel pressure is usually on the order of 35-50 psi. Fuel injectors connect to the rail, but their valves remain closed until the ECU decides to send fuel into the cylinders.
  • Usually, the injectors have two pins. One pin is connected to the battery through the ignition relay and the other pin goes to the ECU.
  • The ECU sends a pulsing ground to the injector, which closes the circuit, providing the injectors solenoid with current. The magnet on top of the plunger is attracted to the solenoids magnetic field, opening the valve. Since there is a high pressure in the rail, opening the
    valve sends fuel at a high velocity through the injectors spray tip.
  • The duration that the valve is open and consequently the amount of fuel sent into the cylinder depends on the pulse width (i.e. how long the ECU sends the ground signal to the injector).
  • When the plunger rises, it opens a valve and the injector sends fuel through the spray tip and into either the intake manifold, just upstream of the intake valve, or directly into the cylinder.
electronic fuel injector diagram
electronic fuel injector diagram

Throttle body injection (TBI) system – Working of electronic fuel injection system 

The throttle body injection (TBI) system uses one or two injector valves mounted in a throttle body assembly. The injectors spray fuel into the top of the throttle body air horn The TBI fuel spray mixes with the air flowing through the air horn. The mixture is then pulled into the engine by intake manifold vacuum. The throttle body injection assembly typically consists of the following: throttle body housing, fuel injectors, fuel pressure regulator, throttle positioner, throttle position sensor, and throttle plates.

Throttle Body Injection is an electronically controlled injection system in which an electronic fuel injector injects the fuel intermittently in to the intake manifold at a central point ahead of the throttle valve. The central- injection unit operates at low pressure (0.7 to 1 bar) so; an inexpensive hydrodynamic electric fuel pump can be used (generally in the form an in-tank unit). The injector is flushed continuously by the fuel flowing through it in order to prevent the formation of air bubbles. The injector is a solenoid – controlled valve. The central injection unit uses the throttle valve to meter the intake air while injecting the fuel intermittently above the throttle valve. The intake manifold then
distributes the fuel to the individual cylinders. Various sensors monitor all important engine-operating data, which are then used to calculate the triggering signals for the injectors and other system actuators.

throttle body injection system
throttle body injection system

Testing of Electronic Fuel Injector :

Ohm-meter test for electronic fuel injector. 

Following are the steps of the Ohmmeter test for electronic fuel injector:
• An ohmmeter is connected across the injector terminals to check the injector windings after the injector wires are disconnected.
• If the ohmmeter reading is infinite, the injector winding is open.
• An ohmmeter reading below the specified value indicates that the injector winding is shorted.
• A satisfied injector winding should have resistance between 0.3 to 0.4 ohms.
• Replace the injector if the results do not have the resistance as specified by the manufacturer.

electronic fuel injector testing
electronic fuel injector testing

Sound test for testing electronic fuel injector

Procedure for sound test for testing electronic fuel injector:

The use of auto fuel injectors is a sophisticated way to provide the right fuel and air mix to an engine for a vehicle. The small cylindrical fuel injectors play a specific role in a larger fuel intake system, along with other elements like the fuel pump and the fuel tank. Over time, fuel injectors may need to be maintained or checked for proper functioning.

1) The electronic fuel injection system relies on electronic signals that control how these items operate
2) Along with checking a fuel injector electronically, you can listen for certain kinds of sounds that will tell you when a fuel injector might not be working correctly.
3) A clunking sound or similar warning sound may show that the fuel injector is not functioning the way it should.
4) If the injector electrical leads are difficult to access, an injector power balance test is hard to perform. As an alternative, start the engine and use a technician stethoscope to listen for correct injector operation.
5) A good injector makes a rhythmic clicking sound as the solenoid is energized and de-energized several times each second.
6) If clunk- clunk instead of steady click-click is heard, chances are the problem injector has been found.
7) Cleaning or replacement is in order.
8) If an injector does not produce any clicking noise, the injector, connecting wires, or PCM may be defective.
9) When the injector clicking noise is erratic, the injector plunger may be sticking.
10) If there is no injector clicking noise, proceed with the injector resistance test and light to locate the cause of the problem.
11) If a stethoscope is not handy, use a thin steel rod, wooden dowel, or fingers to feel for a steady on/off pulsing of the injector solenoid.

Advantage of an electronic fuel injection system: 

1. Improved power output.
2. Better fuel efficiency over a wide range of engine speeds.
3. Quick warm-up of engine.
4. Reduced engine emission that meets strict emission norms.
5. Better throttle response of the engine.
6. Better pick- up (acceleration).
7. Compact design of the fuel supply system.
8. Modular design.
9. Engine performance is maintained under various loads and atmospheric pressures (altitude).
10. Engine need not be tuned from time to time as in the case of a carbureted engine fuel supply system.
11. Engine idle speed is controlled by a microprocessor and so precisely controlled.
12. The vapor lock problem does not occur, as EFI system uses an electric fuel feed pump. The pump maintains sufficient pressure in the fuel line to avoid vapor lock in hot weather.
13. Improved atomization. Fuel is forced into the intake manifold under pressure that helps break fuel droplets into a fine mist.
14. Better fuel distribution. Equal flow of fuel vapors into each cylinder.
15. Smoother idle. Lean fuel mixture can be used without rough idle because of better fuel distribution and low-speed atomization.
16. Lower emissions. Lean efficient air-fuel mixture reduces exhaust pollution.
17. Better cold-weather drivability. Injection provides better control of mixture enrichment than a carburetor.
18. Increased engine power. Precise metering of fuel to each cylinder and increased airflow can result in more horsepower output.
19. Fewer parts. Simpler, late model, electronic fuel injection system have fewer parts than modern computer-controlled carburetors

Disadvantages of Electronic Fuel Injection System :

  • The biggest disadvantage with electronic fuel injection systems is that they are expensive.
  • EFI conversions are not cheap, in fact they are usually expensive. Steer clear of modern car’s EFI systems, they aren’t readily programmable and are difficult to get working correctly.

More Resources /articles

Mechanical Subjectwise Basic Concept Notes ,Articles

Automobile Trends , News articles , Notes

Automobile Engineering Parts and System Notes , Article


Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Recent Posts