Electronic Fuel Injection Basics

Today, more than 95 percent of the vehicles produced have some form of electronic fuel injection (EFI) instead of carburetors. There are a number of reasons why EFI has become the fuel delivery system of choice for the world’s automakers. Among them: improved drivability and reliability, and ease of diagnostics and service.

Basic Theory
Modern electronic fuel injection consists essentially of a pressurized fuel source, a solenoid valve (commonly called a fuel injector) and an electronic controller/computer. When the solenoid is energized, fuel sprays out into the valve port. Fuel is delivered to the injector by a high-pressure electric pump at around 40 psi. Fuel delivery is controlled by the injectors, which are cycled by the computer.

Siemens’ innovative piezo-based injectors for diesel engines overcome the associated louder engine sound previously heard when employing greater fuel injection pressures.

The computer produces a signal to open the injectors for a certain length of time depending on engine conditions relayed by sensors. The longer that the injector is open, the more fuel is injected. As engine load and rpm are increased, the injector open times are increased to match inreasing airflow. This computer output signal is called the injector pulse width. The longer the pulse width, the more fuel is injected.

EFI Types

Modern electronic fuel injection (EFI) systems employ highly sophisticated computer-designed electric solenoids (injectors), like this Siemens VDO piezo diesel engine injector, for precise fuel metering and delivery every time.