High On EFI

What It Is, How It Works, & Why We Love It!

By Karl Brauer

Photography by Karl Brauer

What Is Fuel Injection?

Looking through the collector car ads for an unrealistically great deal on a Ferrari (something moto-weenies do on a regular basis) one notices that the typical price for a used 󈨔 308GTS differs substantially from the price on a &821782 308GTSi; usually the GTSi carries about a $5,000 price premium. So what gives? Is that little i really worth an extra 5K?

Well, as you might have already guessed, the i is a European designation meaning "injecktione;" as in fuel injection. And if you can get it on a Ferrari, or on any car, for a mere $5,000 over the price of a carbureted model, consider it a bargain.

What makes electronic fuel injection, or EFI, so much better than carburetion, and why is it used almost exclusively by today's automobile manufacturers? To answer that, you must first understand the basic components that make up a modern fuel injection system. First there's a computer module that acts as the "brains" of the system. This module is fed information from a number of sensors to determine exactly how much fuel is required by the engine at any given time. After retrieving this information, the computer opens the injectors to get the correct air/fuel mixture into the combustion chamber.

While fuel injection systems can vary between different vehicle manufacturers, all of them utilize these three basic components, which we'll discuss in greater detail.

The Computer

Experts say the average new car possesses more computing power than the entire lunar module that put Neil Armstong on the moon in 1969. That doesn’t mean you should seek out new life and new civilizations in your Honda Civic. It does, however, mean that a lot is going on under the hood of your car and that computers control most of it.

By utilizing the power of the integrated circuit board, engine controllers can monitor everything from barometric pressure to ambient temperature to throttle position in determining just how much fuel an engine needs. With hundreds of calculations going on every second, the computer is always ready to make necessary adjustments with regard to fuel management. Of course, like any computer, engine controllers are only as smart as the people who program them and sometimes they still need a little help (see sidebar: EFI Hackers).

The Sensors

The decisions made by an engine controller are based on multiple sensors located throughout a vehicle’s engine compartment. The basic sensors necessary for any EFI system are the rpm sensor, the manifold absolute pressure sensor (MAP) or mass air sensor (MAS), and a throttle position sensor. These three sensors, plus a computer and fuel injectors, can make up a very basic fuel injection system. While most current passenger cars use additional sensors and are more complicated, race teams often stick to this basic fuel injection design for ease of maintenance and tuning.

Some additional sensors in use on modern EFI systems include an oxygen sensor to reduce emissions, a coolant temperature sensor to aid cold-starting, and an ambient air temperature sensor to adjust for changing weather conditions. There's also a barometric pressure sensor that measures air density when driving at different altitudes.

If one or more of these sensors fails, the information received by the engine controller will be inaccurate. This could result in something as minor as rough idling or poor gas mileage to something major like a complete engine shut down. Of the many sensors in use today, oxygen sensors are probably the most common to wear out or fail.

The Injectors

After the engine controller receives information from the various engine sensors, it uses this data to compute precisely how much fuel is required for a given driving situation. This can range from idling in rush-hour traffic to driving over mountains at 10,000 feet above sea level. Remember that the engine controller is analyzing and computing fuel needs constantly to make the necessary adjustments for proper fuel delivery.

The final piece in the fuel injection puzzle is, appropriately enough, the fuel injector. The injector operates by allowing a very specific amount of fuel into the combustion chamber via computer control. The majority of today's engines use one injector per cylinder. During engine operation, a small plunger inside the injector opens for a given amount of time, referred to as the pulse width, to allow pressurized fuel to flow into the combustion chamber.

By varying the amount of time the plunger stays open, the engine controller can produce a very specific air/fuel mixture, (about 14.7 parts of air for one part fuel) to maximize fuel efficiency. If the engine controller is properly programmed and the sensors are supplying valid information, a fuel injected engine can automatically maintain the correct air/fuel ratio under a wide variety of changing conditions.

In contrast, a carbureted engine would need constant manual adjustments even to approach EFI's level of accuracy. This is because a carburetor depends on a combination of engine vacuum and mechanical pieces to deliver fuel to an engine and, thus, is much less accurate than a computer-controlled sensor-activated EFI system.

How To Make It Better

We&8217ve established that fuel injection is superior to carburetion in efficiency, but can a stock EFI system be improved upon with aftermarket upgrades? The answer, of course, is yes; but you have to know what you’re doing. Since the key to performance is maintaining the proper air/fuel mixture, you don’t want to increase an engine’s fuel delivery until you increase its airflow. You can do this with freer-flowing intake and exhaust systems as well as by upgrading from a mass-airflow sensor to a manifold absolute pressure sensor, since the latter allows for better intake airflow.

Once you have increased an engine's airflow, you will also want to raise its fuel delivery capabilities. Small increases in airflow can often be compensated for by the engine controller and stock injectors, but serious upgrades require altering the factory fuel system. This can be done by changing the stock computer's fuel delivery program at places like G-Force in Torrance, California.

Depending on the hardware capabilities of the factory fuel system an updated computer program may be all that's necessary. Most factory fuel injectors have a certain amount of "reserve" capability that can be tapped into for increased fuel delivery. If an individual's performance demands cannot be met by the factory fuel system, several companies offer upgraded pieces like stronger fuel pumps and larger injectors. RC Engineering (also in Torrance, California) offers custom racing injectors in any size from 210 cc up to 1,680 cc. The company will also clean and balance factory injectors to help get the most out of stock components.

Final Words

While the carburetor had its place in automotive history, by today’s standards it’s just that--history. Computers, engine sensors, and fuel injectors have changed the process of fuel delivery from a sloppy hit or miss proposition to a precisely controlled science with more powerful, efficient, and cleaner-running engines as the payoff.

So if you see a great deal on an early '80s Ferrari, make sure it has the little i after the GTS. And if it's a really great deal, give us a call.