by John Gregory

Created on: June 29, 2010   Last Updated: June 30, 2010

Electronic Fuel Injection Explained.

You may think it intimidating, but when you understand the philosophy of electronic fuel injection, it all becomes clear.

Introduction

For efficient fuel consumption and optimum performance from an internal combustion engine, the air-fuel ratio must be as near to the ideal as possible all the time the engine is running. When all the the free oxygen in an engine cylinder, on an inlet stroke, combines with all fuel delivered into that cylinder’s combustion chamber, the air/fuel mixture is chemically balanced.  Keeping the air/fuel ratio as ideal as possible is an important measure to ensure low-pollution exhaust emissions, and also for performance tuning reasons.

For gasoline the ideal air/fuel mixture is approximately 14.7 parts air to 1 part gasoline. Less than 14.7 parts of air to 1 part gasoline is considered to be a rich mixture, more than 14.7 to 1 is a lean mixture. The actual air/fuel mixture being used by an engine at any one time, divided by the ideal air/fuel mixture is known in automotive technology as lambda. The math show us a lambda value of 1 is ideal, a rich mixture will be less than one, and a lean mixture will be greater than 1.   

The Modern Electronic Fuel Injection System

At the core of nearly all modern fuel injection systems is the fuel rail. This carries fuel supplied from an electric pump mounted near the fuel tank, and keeps the system pressurized and free from air-locks. When the engine is running, the pressure of the fuel in the fuel rail varies continually, in line with the fuel requirements of the engine. A pressure valve in the system is used to regulate the pressure of the fuel in the fuel rail and allows excess fuel to be returned to the tank.

The fuel is introduced into the engine via a set of fuel injectors. There may be just a single injector, or there may be one injector for each cylinder of the engine. The injectors are fed by the fuel rail, and spray atomised fuel into the inlet manifold ports. The amount of fuel delivered into the engine from the injector(s) is constantly adjusted by the ECU (the Electronic Control unit) by varying the amount of time that the injector(s) is/are open. For this to work efficiently and precisely, the difference in pressure between the fuel in the injector(s) supplied by the fuel rail, and the air pressure in the inlet manifold must stay constant. This is achieved by using the pressure valve that controls the pressure of fuel in the

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