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The objective of Electronic Fuel Injection System is to regulate and optimize the fuel/air ratio that enters a vehicle’s engine. Fuel injection has recently become the main fuel delivery system used in automotive petrol engines. This post will discuss what is Electronic Fuel Injection System (EFI), its architecture, types, how it works, applications, advantages and disadvantages.

What is Electronic Fuel Injection System (EFI)

A system which aims at optimizing fuel/air ratio entering a vehicles engine is referred as Electronic Fuel Injection System. EFI System has almost completely replaced usage of carburetors.

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Fig. 1 – Introduction to Electronic Fuel Injection System

Carburetors are good for performance, but due to their vague nature, they can’t make great horsepower, get solid gas mileage, and pass an emission test, all with the same tune, they also had many mechanical parts that could become gummy over period. This means they were more maintenance-intensive, with a carburetor rebuild often being part of a routine maintenance schedule.

OEM’s looked to EFI to resolve their complex emission problems. The initial EFI was mostly just processor controlled carburetors attached to an oxygen sensor and throttle position sensor, all wired to an Electronic Control Unit.

The Electronic Fuel Injection System consists of electronic components and sensors. It has to be kept clean and well calibrated to boost the engine’s strength and efficiency and to cut down gas consumption.


Fig. 2 – Fuel Injector (a) Two Wheeler (b) Four Wheeler

Types of Fuel Injection

To understand the concept better, we first have to understand types of Fuel Injection. The Fuel Injection types used in newer cars are:

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

Single-Point or Throttle Body Injection

The first and simple kind of Fuel Injection was the Single-Point injection. Here the carburetor is replaced by one or two fuel injector nozzles in the throttle body, which is the throat of the engine’s air intake manifold.

Single-Point Injection was a stepping stone to the more complex multi-point system for some manufacturers. They are economical and easier to service.

Port or Multi-Point Fuel Injection

In Multi-point Fuel injection a separate injector nozzle is devoted to each cylinder, right outside its intake port, due to which the system is also called Port Injection System. When the fuel vapor is shot close to the intake port it makes sure that fuel is drawn completely into the cylinder.

The major benefit is that MPFI meters fuel more precisely than the TBI designs do. It is better at achieving the desired fuel/air ratio and improving all related aspects. Also, it nearly eliminates the possibility of the fuel to condense or to get collected in the intake manifold. The TBI and carburetors are designed in such a way that the intake manifold conducts the engine’s heat which is the measure to vaporize liquid fuel.

It is not necessary on engines that are equipped with MPFI where the intake Manifold can be made out of lighter-weight material, even plastic. MPFI system results in increased fuel economy. Standard metal intake Manifolds have to be positioned on top of the engine to conduct heat, but in case of MPFI it can be positioned more creatively, granting the engineers design flexibility.

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Fig. 3 – (a) Single-point or Throttle Body (b) Port or Multi-Point (c) Direct Engine Fuel Injection System

Sequential Fuel Injection

Sequential Fuel Injection, also known as the Sequential Port Fuel Injection (SPFI) or Timed Injection, is a type of Multi-Port Injection. Although the MPFI has multiple injectors, they all spray their fuel at the same time or in groups. This may result in “hanging around” of the fuel in a port for as long as 150 milliseconds at the time of engine idling.

It may not seem like much, but it’s sufficient of a limitation that the engineers addressed it i.e. Sequential fuel injection triggers every injector nozzle separately. They are basically timed like the spark plugs and spray the fuel immediately before or as their intake valve opens. Although seems like a minor step, the efficiency and emission improvements come in exceptionally small doses.

Direct Injection

Direct Injection injects fuel straight into the combustion chambers, past the valves. Direct Injection system is common in diesel engines and is beginning to pop up in gasoline engine designs, sometimes called DIG for Direct Injection Gasoline. Fuel proportioning is still more accurate than in the other injection system.

The Direct Injection grants engineers an additional variable to influence precisely how combustion occur in the cylinders. The discipline of engine design scrutinizes how the fuel/air mixture swirls around in the cylinders and how the explosion travels from the ignition point. Direct Injection is one that can be used in low-emission lean-burn engines.

Architecture of Electronic Fuel Injection System

Components of the Electronic Fuel Injection System include:

  • Sensors
  • Electronic Control Unit (ECU)
  • “Check Engine” Light / “Service Engine Soon” Light
  • Fuel Injectors
  • Fuel Pump

FIS (1)

Fig. 4 – Schematic Diagram of Electronic Fuel Injection System


Sensors are installed in numerous points of the engine and their function is to send out information to the ECU. The following sensors are used:

  • Engine Temperature Sensor
  • Intake Temperature Sensor
  • Exhaust Temperature Sensor
  • Engine Speed Sensor
  • Throttle Position Sensor
  • Probe which is responsible for the measurement of the fuel concentration in the fuel/air mixture

Actuators are components that obtain information from ECU and they act in the feeding system, varying the volume of fuel that the engine receives.

It uses following actuators:

  • Fuel Injector
  • Spark Plug
  • Throttle

Electronic Control Unit

The Electronic Control Unit is responsible for the measurement of the sensors and the estimation of the action for each actuator with regard to timing restrictions. The block diagram of the Fuel Injection System is as shown in the Fig. 3. The time constraints of the system are imposed by the characteristics of the internal combustion engine to be controlled.

It is defined that a turn of the engine i.e. 360° is completed once in every 5 micro seconds for 12,000 rpm. The actuator of throttle valve considers the position of 0° as a pulse of 1 milli second and 90° as a pulse of 2 milli seconds, within a period of 25 milli seconds. Considering these timing constraint, the reading of the sensors and the calculation of the acting times for the actuators should be processed in at most 15 milli seconds.

“Check Engine” Light / “Service Engine Soon” Light

The “Check Engine” Light (or “Service Engine Soon” Light) on the console comes on during the scan and goes off when all sensors are functional.

Fuel Injector

It helps in injecting fuel into the engine’s intake ports.

Fuel Pump

It helps in pumping gasoline from the vehicle’s fuel tank to the engine and distributes fuel to Fuel Injection System under higher pressure.

How EFI System Works

The Fuel Injection System consists of many sensors positioned all around your vehicle as shown in the Fig. 5. Every time you start your vehicle, the Electronic Control Unit (ECU) scans each and every one of these sensors to verify their functionality.

The “Check Engine” Light (or “Service Engine Soon” Light) on the console comes on during the scan and goes off when all sensors are functional.

Block Diagram new

Fig. 5 – Block Diagram of Electronic Fuel Injection System

The sensors continuously detect the values of numerous parameters like air pressure, air temperature, throttle angle, air density, fuel temperature, fuel pressure, oil pressure, coolant temperature, exhaust temperature, crankshaft angle, timing, engine rpm, speed, etc.

All these data are processed through the ECU (Electronic Control Unit) to establish the amount of time the Fuel Injectors are open, injecting fuel into your engine’s intake ports. The injectors usually are open only for a few milliseconds at a time. A fuel injector consists of a nozzle and a valve. The power to inject the fuel comes from a Fuel Pump or Pressure Container located far back in the fuel supply. The fuel going through the system is atomized by forcibly pumping it through a small nozzle under very high pressure.

Applications of Electronic Fuel Injection System

The applications include:

  • EFI System incorporates the state of the art control software routine for emission, fuel consumption and performance demands
  • The System also incorporates a technology of Smart Ignition for control of the ignition system, by providing OEMs the flexibility to achieve best in class fuel consumption

Advantages of Electronic Fuel Injection System

The advantages are:

  • Enhancement of volumetric efficiency of the engine
  • Direct fuel injection into the cylinder eliminates manifold wetting
  • Good atomization of fuel even at low speed as atomization is independent of cranking speed
  • Less knocking because of the improved atomization and vaporization
  • Ice formation at throttle plate is eliminated
  • Fuels of low volatility can be used as distribution is independent of vaporization
  • As variation of fuel/air ratio is almost negligible it results in good engine performance
  • The height of engine can be less as the position of injection unit is not so critical

Disadvantages of Electronic Fuel Injection System

The disadvantages include:

  • High maintenance cost
  • Difficulty in servicing
  • Possibility of malfunction of some sensors
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