Electronic Fuel Injection System Diagram and Working Principle

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The electronic fuel injection system is a new innovation in gasoline engine, this system incorporates electronic computerizm to get the best fuel and air comparisons under all engine conditions.

The EFI system basically has the same diagrams as conventional fuel systems. However, the EFI system does not equip with carburetor. Instead, the injector will be placed in front of the intake valve in each cylinders.

Then how about the diagram of electronic fuel injection ? below we will learn a basic schematics of EFI system for you to understand easily.

A. Fuel Line diagram of EFI system


As seen above, the efi system has a fairly simple diagram of fuel lines. The fuel will be moved directly from the tank to the injector. The flow of gasoline in the EFI system is more like this,

  1. Gasoline inside the tank will be pumped by an electric pump located inside the tank (sink).
  2. Gasoline from the pump will flow through the fuel filter. In the fuel filter, the gasoline will be filtered from any dust or dirts.
  3. After passing the fuel filter, the gasoline will be inserted directly into the delivery pipe. The delivery pipe has multiple channels that directly connected to each injectors.
  4. When one of the injector solenid opened, the gasoline will spray out. To adjust the amount of gasoline that sprayed, the ECU will adjust the duration of the injector solenoid opening time.


Perhaps there is a question, why does gasoline spray out when the solenoid open?

There is a difference pressure between intake manifold and inside the injectors (actualy, the pressure inside the injector is greater than the pressure inside the intake). Thus, the gasoline inside the injector will spray out into the intake manifold that has lower pressure.

How to make the fuel pressure inside the injectors greater ?

This is the task of electric fuel pump, the fuel pump will pump the gasoline from the tank to the delivery pipe. That is, the fuel pump does not just deliver gasoline from the tank to the engine, but also raises the gasoline pressure constantly.


B. The diagram of Electronic fuel injection


For efi circuit, might be more complicated. However, we will explain a basic of EFI system schematic with a very simple circuit.

As shown in the image, this circuit consists of three main components. They’re sensors, ECU, and actuators. The sensor will be an indicator or benchmark of the ECU in computing, while the actuator is used as the executor of the result of the ECU calculation (eg injector and fuel pump).

If explained, maybe the circuit will be like this

  1. IAT and MAF sensors, will detect air temperature and the mass of air that flowing passing the filter. This will be an early indicator to determine how much gasoline is needed.
  2. The TP sensor will detect the opening angle of the throtle valve, it will know the RPM desired by the driver (the higher the RPM the more gasoline it will take)
  3. CKP and CMP sensors will give the info to determine when the injector is open, this will make the gasoline spray out fitting during the intake step.
  4. O2 sensor, served as feedback or correction of the combustion results, whether the combustion works perfect or premature. Data from O2 sensor, will be used to improve AFM (air fuel mixture). This sensors, locate inside the exhaust manifold.


The data from the above sensors, will form a voltage with a certain value. Each voltage value, has different information to what is measured. The ECU will translate all these voltage values, and perform the calculations. The results, is also in the form of voltage.

There are two outputs from the ECU, first ECU output to the injector and second to the fuel pump. The output voltage from the ECU to the injector has a duration, the duration will affect the amount of gasoline sprayed. While the ECU output to the fuel pump, has a value variation. The greater the voltage the greater the pressure generated by the pump, this makes the amount of gasoline coming out of the injector more and more.

From the above explanation, I think it is quite clear how the EFI system works. Hope can increase our insight.