The computer

From Edmunds.com

If you're reading this article, you already know that computers play a major role in just about every aspect of human existence. Besides supplying information for Web surfers and entertaining games for kids (and adults), they also control most of what goes on in today's automobiles. You may have heard that the average new car possesses more computing power than the entire lunar module used to land our first astronauts on the moon. Much of this processing power is necessary in a modern fuel-injection system.

The computer at work under your hood is often referred to as the engine controller. It monitors everything from barometric pressure to ambient temperature to throttle position, in order to determine just how much fuel an engine needs. By constantly monitoring the conditions under which an engine is running, the engine controller is able to make infinite adjustments for maximum efficiency and performance. It should be noted that the engine controller performs this task not only by adjusting fuel delivery but by altering the ignition system as well. Certain forms of variable valve timing also use computer control to deliver peak performance.

The sensors
A computer is only as capable as the information supplied to it, right? To keep the engine controller properly informed, a number of sensors are utilized for monitoring purposes. The three basic sensors required by every EFI system are an RPM sensor, a manifold absolute-pressure sensor (MAP) or a mass air sensor (MAS), and a throttle-position sensor. Most modern cars use several additional sensors to monitor things such as barometric pressure (for altitude changes), exhaust gases (for emission reduction), and temperature (for a proper mixture when an engine changes from cold to hot).

Sensor failure is a common cause of reduced horsepower or mileage.

If one or more of these sensors fail, engine performance will suffer or stop altogether. Sensor failure is a common cause of reduced horsepower or mileage, especially on American cars from the 1980s when domestic fuel injection was in its infancy.

The injectors
The information gathered by the various EFI sensors determines exactly how much fuel is necessary. The engine controller uses this information to adjust for conditions ranging from idling to accelerating to highway cruising. A device, called the fuel injector, delivers this precise amount of fuel into the combustion chamber through a small plunger located in the nozzle of the injector. Since the plunger can open and shut very quickly, it makes the injector extremely accurate at modulating fuel flow and allows fuel injection to adjust for both small and large variations in the operating conditions.

EFI's accuracy is based not only on the amount of time the plunger stays open (called a pulse width) but also on the fuel pressure within a fuel-injection system. This makes the fuel pump a much more crucial element and explains why most modern fuel pumps are electric rather than mechanical.

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