Electronic Fuel Injection: Definition, Types, Principle, and Components

What is Electronic Fuel Injection?

Electronic Fuel Injection is a fuel spray system that works electronically controlled so that the mixture of air and fuel always follows the fuel motor’s needs.


Thus, the chamber’s combustion will occur correctly to obtain optimal motor power and environmentally friendly exhaust gases. The method of fueling the ECU (Electronic Control Unit) to the injector is based on signals from sensors, such as:

  • engine speed sensor
  • water temperature sensor
  • airflow meter sensor
  • absolute pressure manifold
  • Throttle position sensor, etc.


Electronic Fuel Injection Working Principle

The electronic fuel injection system is separated into sensors and actuators. Sensors act as providers of information about conditions related to determining the amount of petrol that must be injected. The provision of that information can be either analytical or digital signals. Examples of sensors that send data in analog form are mass airflow and Throttle Position Sensors (TPS).



EFI system

While the actuator is a component whose operation is regulated by the ECU in an analog or digital way, analog commands are given to the electric gas pump and engine control lights. In contrast, digital signal commands are given to the injector, ignition coil, tank breather valves, idle regulator, and lambda sensor heaters.

Electronic fuel injection VS Carburetor

The following is the difference between EFI and carburetor system when the car engine temperature is cold and accelerating.

The Carburetor System

In the carburetor system, the petrol supply when the car engine is cold will be regulated by minimizing air intake.

Carburetor system

Thus, the fuel will come out richer, and the arrangement is made by a choke circuit that works automatically or mechanically. Furthermore, the fuel supply is regulated by the value of the engine vacuum level—the greater the vacuum’s value, the greater the supply of fuel to be provided.

Carburetor system during acceleration

The acceleration circuit will provide the gas supply in the carburetor system during acceleration. The acceleration circuit is carried out by a lever connected to a tilt arm.

Meanwhile, the tilt arm is driven by throttle valve acceleration, and then the gasoline will come out through the pump jet toward the venture.

The EFI System

In the EFI system, fuel supply when the engine is cold will be determined by the ECU (Electronic Contro Unit) based on engine operating temperature conditions and air pressure value at the intake manifold.

EFI system during engine acceleration

The fuel supply during the engine accelerates regulated by the ECU based on information on the amount of air flowing through the intake manifold measured by the airflow meter. From this data, the ECU will instruct the injector to add gasoline to be injected.

Electronic Fuel Injection System Types and Components

EFI system is divided into two types, namely Type D and L.

EFI Type D

In EFI type D, the measurement of air entering the intake manifold is carried out by a vacuum sensor.

EFI type D

The pressure value in the intake manifold is used as information for the ECU. Also, it is used as a determinant of the amount of gasoline to be injected.

EFI Type L

In EFI type L, the value of air entering the intake manifold is measured using an airflow meter. It is used as information for the ECU to determine the amount of petrol to be injected.

EFI type L


EFI Components

The following are Electric Fuel Injection components and their functions.


  1. Fuel pump: Suck fuel from a tank and press it to the delivery line to be ready for injection
  2. ECU: Processing data received from sensors and giving commands to components to operate.
  3. Speed Sensor: Detects vehicle speed
  4. Data Link Connector: Diagnose the working of the system
  5. Variable Resistor: Adjusts the fuel and air mixture level
  6. Throttle Sensor: Detects the size of the gas valve opening
  7. Pressure Sensor: Detects/measures the amount of pressure in the intake manifold
  8. Idle Speed Control: Adjust engine idle speed
  9. Injector: Receives an order to inject a certain amount of fuel
  10. Cam Angle Sensor: Knowing the size of the cam angle
  11. Crank Angle Sensor: Detects high or low engine speed
  12. Knocking Sensor: Detects engine knock.
  13. Temperature Sensor: Monitor high and low water temperatures


Fuel Pump

Fuel pumps commonly used on engines with EFI systems are electric gas pumps that function to suck fuel from the tank and press it into the fuel system.

The pumps that are commonly used are “in-tank” and “inline” types. In-tank type means the fuel pump is in the tank submerged in petrol. While the type inline means the fuel pump is outside the fuel reservoir.

In the series, the work of the petrol pump is monitored by the ECU. If the transistor on the ECU is OFF, the electric current does not flow into the mass. Thus, the pump relay is off. As a result, the battery’s electric current does not go to the pump, and the pump cannot work.

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Electronic Control Unit

The electronic Control Unit is a component of the fuel system that receives electrical signals from sensors. Furthermore, the sensor is processed into a command line to the actuator.

Electronic Control Unit

The ECU gets the mains supply from the battery and is forwarded to the sensor and actuator. The voltage value is adjusted to the capacity of the sensor or actuator.

Explanation of ECU Parts and their functions

  • Micro Processor: Set the order and make decisions about data that has been treated based on information from data storage in system memory.
  • Memory: Store input data that is ready to be informed to the microprocessor
  • Input: provides information in the form of an electrical signal to memory for processing by a microprocessor.
  • Data Acquisition: Data that a microprocessor has treated is distinguished and then informed to the output
  • Output: The electrical signal generated by the data acquisition given to the actuators

Data Link Connector

Data Link Connector is a collection of codes to facilitate the detection of work from sensors or actuators. DLC is applied to all vehicles with EFI systems as a connector to diagnose the working system through specific software. To detect it manually is by jumpers codes with other codes under each vehicle’s manual book or brand of the car.

Variable Resistor

The variable resistor functions to regulate the fuel mixture at idle speed. Adjustment aims to produce the correct co value, so do not adjust the variable resistor without using a CO tester.


If the fuel mixture is excessive, change the variable resistor by turning the adjusting screw with SST clockwise. Meanwhile, if the adjusting bolt is turned counter-clockwise, it indicates that the fuel is too lean.

Throttle Sensor

The throttle sensor will detect the amount of gas valve opening. The gas valve movement will move the slider or friction arm, which affects the value of the resistance. The ECU will determine the quantity of gasoline that will be injected based on this information.

The throttle sensor is fitted on the throttle body, which detects the throttle valve’s opening angle. When the throttle valve is fully closed, a voltage of 0.3 +- 0.8 Volt will be provided by the ECU through the VTH / VTA terminal.

Meanwhile, if the throttle valve is open, the ECU’s voltage to VTH / VTA will increase according to the throttle valve opening angle. The voltage value becomes 3.2 to 4.9 volts when the throttle valve is open. The ECU considers driving conditions based on the input signal and uses it to determine the correct air-fuel ratio, power gain, and fuel cut control.

Pressure Sensor

A pressure sensor is attached to the intake chamber to detect the air pressure condition at the intake manifold. The pressure value at the intake will be informed to the ECU as an analog input.

pressure sensor

Idle Speed Sensor

Idle speed control is fitted on the lower part of the throttle chamber and regulates the air given at idle rotation. The ECU only operates the ISC valve to make idle ups and provide feedback to achieve the idling rotation target.


The injector is one part of the fuel system so that a homogeneous mixing process between air and fuel becomes possible. Injectors have plungers that can open or close fuel lines.

EFI injector

Based on instructions from the ECU engine, the solenoid controls the work of the plunger. More fuel will come out if the plunger holding time is more prolonged and vice versa. The excess fuel mixture, lean, and injection time settings depend on the signal sent by the ECU engine.

Cam Angle Sensor

The cam angle sensor is mounted on the cylinder head’s upper side to detect any change in the cam angle movement. The sensor will notice changes in the camshaft angle associated with the inlet valve. Furthermore, the signal is considered by the ECU to start fuel injection or end it.

Crank Angle Sensor

Crank Angle Sensor will detect engine speed and piston location of every cylinder.

Temperature Sensor

The water temperature sensor functions to detect the cooling water heat condition, and it is installed in the engine block or at the bottom of the thermostat housing. The sensor will work according to the resistance value. The higher the temperature of the cooling water, the smaller the resistance and vice versa.

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The cooling water sensor is linked to the ECU engine, which provides a 5 Volt power source voltage to the sensor via a resistor from the THA / THW terminal.

When the resistance value changes according to changes in the cooling water temperature, the potential at the THA / THW terminal will also change. Following these signals, the ECU adjusts the fuel injection volume to maintain engine performance during operation.

Knocking Sensor

The knocking sensor will detect the symptoms of knocking on the engine because if it takes place in the combustor, the ECU will set the ignition more forward or backward to eliminate knocking.

Electronic Fuel Injection Classifications

According to the Fuel Spray Area

Based on where the gasoline is sprayed, the EFI system is divided into direct and indirect injection.
Direct injection: The injector injects the gasoline straight into the burning chamber.

In contrast, indirect injection: The fuel is not instantly injected into the combustor but through the intake manifold.

According to the Fuel Spraying Rhythm

  • Simultaneous Model

The simultaneous spraying rhythm means that the gasoline is injected into the firing chamber continuously. Or in other words, fuel spraying does not take into account the working conditions of the engine. It is spraying simultaneously on all cylinders per one crankshaft rotation (360 degrees).

  • Model Grouping

In the grouping model’s spraying rhythm, petrol is injected into the burning chamber continuously following the cylinder group.
Fuel spray takes into account the condition of the engine working steps. It is spraying simultaneously on all cylinders every 720 degrees or two full rotations of the crankshaft.

  • Sequential Model

In the sequential spraying rhythm, gasoline is continuously injected into the combustor following FO (Firing Order). Fuel spray considers the working conditions of the engine and simultaneously on all cylinders every two crankshaft turns (720 degrees).

According to the Fuel Spraying Service

There are two spraying fuel models into the intake manifold, namely single point injection and multi-point injection.

Single Point Injection (SPI)

In this model, fuel spraying will be done by an injector in the intake manifold before the throttle valve. The injected fuel will be sucked in according to the work of each cylinder engine. One injector serves all cylinders, and this is almost the same as a conventional fuel system.

Single Point Injector

The mixture of fuel and air in the intake manifold will wait for the inlet valve to open. As a result, it causes deposition along the intake manifold and becomes a disadvantage to the single-point injection system.

Model Multi-Point Injection (MPI)

The point of spraying fuel is in each inlet into the cylinder. Thus, the efficiency of fuel intake per cylinder is better.

Multi-Point Injection

Based on the construction of the control system, the EFI system is divided into:

  • mechanical injection
  • Electronic Mechanical Injection
  • electronic injection
  • Engine management system.

Mechanical Injection

In this system, the fuel-injected occurs mechanically, where the throttle valve movement will regulate the amount of air needed by the engine and move the lever. Then the lever pushes the fuel gauge lever to determine the amount of fuel to be injected.

Electronic Mechanical Injection

The electronic, mechanical fuel injection system has an electronic regulating system called the electronic control unit. The control system is limited only at the time of injection. Concurrently, the quantity of fuel that must be injected will be determined by the fuel control arm (mixture control unit).

Electronic injection

EFI supplies fuel requirements where the amount and time of supply are regulated electronically by the ECU engine. The ECU engine will process data informed from sensors and be considered to determine the time and amount of fuel that must be injected.

Engine Management System

The engine management system is an electronic fuel injection system where the ignition system is regulated in 1 unit with the ECU engine. In other words, the ignition system is not separate from the ECU engine.

Electronic Fuel Injection Troubleshooting

The car engine won’t start

Check Components:

  1. Immobilizer
  2. Crankshaft position sensor
  3. Amount of fuel and fuel filter condition
  4. Fuel pump and connection
  5. A leak or air intake-vacuum system condition
  6. absolute sensor manifold
  7. Injectors
  8. camshaft position sensor
  9. connector, cable, and relay ECM
  10. ECM
  11. Electricity-engine / battery connection
  12. Ignition system
  13. Fuel pressure and fuel regulator
  14. Engine coolant temperature sensor

Car engine hard to start

Check Components:

    1. The amount of fuel and the condition of the gasoline filter
    2. Fuel pressure and fuel regulator
    3. Leakage of air intake-vacuum system conditions
    4. Electric-engine / battery connection
    5. Engine coolant temperature sensor
    6. Throttle position sensor
    7. Injectors
    8. Camshaft position sensor
    9. Ignition system
    10. Crankshaft position sensor
    11. connectors, cables, and ECM relays
    12. ECM

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