The Electric Fuel Injection system (EFI) is the modern solution for all modern vehicles

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EFI or Electic Fuel Ignition system has replaced the necessity of carburetors in modern Petrol engines.

An EFI system controls the injection of fuel and air through an Electric Control Unit or ECU.

Therefore, EFI engines ensure more efficiency and generate more horsepower compared to a carburetor-based engine.

What is EFI?

EFI stands for Electric Fuel Injection. EFI is a system that controls the supply of air and fuel mixture to the engine through an Electric Control Unit.

How does an internal combustion engine work?

Before we understand how an EFI system work, it is necessary to have the basics of an internal combustion engine.

To keep the engine running all the time, an Internal combustion engine performs four steps.

These are-

  • Intake
  • Compression
  • Power or combustion
  • Exhaust


engine intake valve

During the intake stroke, the piston goes down and the Intake valve opens, creating scope for the air and fuel mixture to get inside the cylinder chamber.


compression stroke valve position

During the compression cycle, the piston moves up, compressing the air and fuel mixture to a great degree.

Compression builds more air pressure inside the cylinder chamber. 

Power or Combustion

Power or Combustion stroke

At this stage, the spark plug sparks fire to create a blast inside the cylinder chamber.


engine Exhaust valve

The power generated from the explosion during the compression cycle forces the piston to go down again.

At this stage, the exhaust valve opens, creating scope for the exhaust gases to move out of the cylinder chamber.

Once the exhaust gases move out of the cylinder chamber, new air and fuel mixture fills the void.

The astonishing fact is that an average internal combustion engine fires more than 13 times in one second.

What are the differences between a carburetor and an EFI system?

The function of a carburetor-based fuel-injected engine and an electric fuel-injected engine is almost the same.

It is the process and the amount of fuel and air mixture injected into the cylinder chamber that varies in both types of systems.

While the carburetor controls the proportion of the fuel and air mixture injected into the cylinder, an Electric Control Unit controls the proportion in an EFI system.

How does an EFI system work?

An EFI system comprises three sub-systems. These are-

1. Fuel Induction

2. Air Induction

3. Electric Control Unit (ECU)

EFI system diagram

Fuel Induction

An electric Fuel pump creates pressure to ensure fuel flow through the fuel filter.

All the distributor pipes inside the system transfer the fuel to the fuel injectors.

The Electric Control Unit or ECU through a pressure sensor controls the amount of fuel that will be injected through the injectors inside the Cylinder Chamber.

Air Induction

Both fuel and air are necessary for the engine to perform the combustion cycle.

The system includes an air induction system that transmits a sufficient amount of air to the injectors to perform the engine operation.

The ECU also controls the air induction through a sensor.

Electric Control Unit or ECU

The ECU determines the amount of air and fuel that will be injected inside the Cylinder chamber.

The ECU does this through sensors.

An EFI system can have multiple sensors.

These are-

  • Fuel sensor
  • Air induction sensor
  • Temperature sensor
  • Pressure sensor
  • Throttle position sensor
  • Oxygen sensor, and so on

What are the types of Fuel Injection systems?

Four types of Fuel Injection systems are prevalent when it comes to injecting fuel and air mixture into the cylinder.

These are-

  • Single point or throttle body Injection
  • Port or multipoint fuel injection
  • Sequential fuel injection
  • Direct injection

Single point or throttle body injection

Single point or throttle body injection diagram

In a single point or throttle body injection system, one or two fuel injectors injects fuel and air mixture into the engine’s air intake manifold.

Here, one or two injectors are devoted to all the cylinders available in the engine.

Port or multi-point fuel Injection

Port or multi-point fuel Injection diagram

In a multi-point fuel injection system, each of the cylinders will have a separate injector nozzle.

By enhancing the fuel and air mixture ratio, a multi-point fuel injection system tends to bring more efficiency to the engine.

Sequential fuel Injection

Sequential fuel Injection diagram

Sequential fuel injection is another variation of multi-point fuel injection.

While all of the injectors of a multi-point fuel injection system inject fuel and air mixture at a time, a sequential fuel injector system does the same process one after another or according to a pre-fixed timeline.

Direct Injection

Direct fuel Injection diagram

In a direct injection system, fuel and air mixture is injected directly into the cylinder’s combustion chamber.

While Direct injection systems are popular in Diesel engines, they are recently becoming a good part of Gasoline engines as well.

What are the advantages of an EFI system?

One of the primary benefits of an EFI engine is that EFI engines are more efficient than a carburetor-based system.

Due to more flexibility, getting more horsepower and rpm is easier in an EFI system which a carburetor-based system can hardly produce.

At the same time, troubleshooting is much easier in an EFI system.

The powerful onboard diagnostic capabilities along with trouble codes allow the fastest and most convenient troubleshooting.

Another noteworthy benefit of having an EFI system in your vehicle is that these systems bring fuel economy.

Controlled vaporization allows the system to use less fuel, which a carburetor-based injection system can’t provide.

What are the disadvantages of an EFI system?

Despite having multiple advantages, EFI systems are expensive to repair.

Having multiple electrical circuitry and sensors inside the system demands expensive repairs in case the system gets damaged.

Besides, any malfunction in any sensor can make the whole system vulnerable.


1. The engine is not running properly

Probable reasons:

  • Short circuit in the water and air intake temperature signal system.
  • Rich or lean fuel proportion measurement by the ECU ( below -50-degree or above 139-degree)


Bringing the water and air intake temperature back to normal (80-degree)  should solve the problem.

Balancing the fuel pressure regulator and pulsation damper should also solve the issue.

2. Fuel injection problem due to ignition system error

Probable reasons:

  • Misfire may happen if the ignition system does not spark properly.
  • This can also happen due to a heated catalytic converter.


If the problem is with the ignition system, the system needs to be corrected.

Correcting the ignition timing can also help in solving the problem.

3. Problems in the throttle prevent the engine from starting

Probable reasons:

Short-circuit or open-circuit in the throttle signal system.


Solving the open-circuit or short-circuit problem should solve the problem.

4. Knock in the engine

Probable reasons:

A short-circuit or open circuit in the knock signal system does not allow the CPU to send signals.

Therefore, higher knocks make the engine vulnerable.


Repairing the knock signal system and the advanced system should solve the problem.

5. The engine does not start as the Revolution Signal systems G1 and G2 do not work

Probable reasons:

Short-circuit or open-circuit in the Revolution system G1 and G2.


If the revolution system is damaged, replacing the system with a new one should solve the problem.

If one of the two systems is damaged, the other one can keep the system running.

6. The engine does not run due to an air-flow system error

Probable reasons:

An open or short circuit prevents the CPU from calculating the exact amount of air.


Repairing the open and short-circuit problem will solve the problem.

7. Uncontrolled Idle speed due to ISCV system error

Probable reasons:

If the ISCV system does not work, feedback control will not be possible.

As a result, Idle will be running at a fixed duty ratio.


Servicing the ISCV system will solve the problem.

8. The engine stops running due to an error in the vacuum or intake manifold  pressure system

Probable reasons:

An open or short circuit in the intake manifold system prevents the engine from starting.


Repairing the open or short-circuit in the intake manifold pressure system will solve the issue.

Electric Fuel Injection is the modern solution

There is simply no way one can underestimate the capability of an electric fuel injection system.

EFI systems are more reliable and better performing. From lowering fuel consumption and emissions to reducing the maintenance cost, EFI systems are offering it all.

If you are still powering up your vehicle’s engine through carburetors, consider installing an EFI system to power up the vehicle to another level.



Design of Electronic Control Unit .pdf

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