Guide to Electronic Fuel Injection

An electronic fuel injection (EFI) system is found in the internal combustion engine and helps in delivering fuel to the cylinders by means of air pressure from the pump. Most of the electronic fuel injection systems are used for diesel or gasoline systems. The EFI’s firmwares are programmable and allow all common hardware. The advent of EFI has replaced the usage of carburetors. The main difference between fuel injection system and carburetor is that a carburetor depends on the air pressure made by the incoming air whereas a fuel injector atomizes the fuel by means of a small nozzle under high pressure.

Various sensors such as voltage sensor, engine speed sensor, throttle position sensor, coolant temperature sensor, airflow sensor, and oxygen sensor are included in the EFI system to check the correct working of the system. The whole system is managed by the electronic control unit, which operates as a central exchange for data that come from several sensors.

How to do an Electronic Fuel Injection System

All fuel injectors work on the same principle. What differentiates one fuel injector from the other is the flow rating of an injector. It is important to have the correct flow rate of an injector as a low flow rate makes an engine starve and a high flow rate makes tuning difficult. There is a formula to calculate the correct injector flow rate for the application, which is based on the horse power. The formula is given as

Injector flow rate (lb/hr) = engine HP (1) × BSFC (2)/ number of injectors × injector duty cycle (3). 

The correct fuel injector can also be identified by the color on the top of the injector, which denotes the approximate horse power per cylinder. The fuel rail and regulator are the important non-computer component in a do-it-yourself EFI system. The fuel rail supplies equal fuel pressure to all the injectors and the regulator manages the pressure. Today, there are many fuel rails that come with a built-in regulator and stock unit. These advance fuel rails are mainly designed for the oversize fuel supply system.

Next important component is the EFI fuel pumps, which are fully electric and primarily made to pressurize the fuel from 55 to 100 PSI. These pumps push fuel rather than pulling fuels and all the modern EFI fuel pumps are situated in the gas tank. Another overlooked component is the emergency shut off switch, which is a simple fix to the potential problem during accidents. This switch is wired with the fuel relay pump and the switch breaks the connection cutting power to the fuel pump to shut down the pump during accidents.

Finally, EFI needs a computer to control the entire system and manage the fuel flow based on the information provided by the sensors. The computer here is referred as Electronic Engine Control (ECU) and this is fixed based on the engine. This ECU should be connected to a laptop or desktop computer for tuning. There are ready-made ECUs available in the market to make the work easy.

A relay box is used to link the components with the computer. For running OEM computer and OEM injectors, OEM wiring harness is required, and for other systems, custom built pieces are available. The oxygen sensor provides the main feedback for the computer. This O? sensor is placed in the exhaust and sends signal that provides the details of the fuel burned in the engine. The O? sensor measures the fuel burned by means of oxygen ratio in the exhaust. The O? sensor comes in two varieties: one wire and three /four wire. A one wire sensor gives less accurate feedback than the three/four wire. Now, the entire system is ready to work.

The electronic fuel injection system is preferred for its efficient fuel combustion, engine performance, better fuel economy, and decreased polluting exhaust emissions.

For additional resources on electronic fuel injection refer to the following sites:

• Fuel Injection
• Electronic Fuel Injection Overview
• Electronic Fuel Injection
• Overview of Electronic Fuel Injection
• Fuel Injection
• Fuel Map Design
• How EFI Works?
• Introduction to EFI
• Electronic Engine Control
• Oxygen Sensors
• EFI Fuel Systems
• Oxygen Sensor Information
• How Computers Work in Automobiles
• EFI Tutorial
• Sensors