A Beginner Guide to Fuel Injection

The Environmental Protection Agency’s (EPA) rules regarding pollution and fuel economy pushed the auto manufacturers from carburetion to fuel injection. It was happening anyway, but the EPA accelerated the change. Fuel injection brings a manufacturing cost penalty, but is necessary to meet emission and fuel economy goals.

The carburetor, after years of development, was still an imprecise device. Further, the carburetor was generally centrally located on the intake manifold. This resulted in the cylinders closest to the carburetor receiving a richer fuel mixture than the cylinders farthest away. In order to not damage the cylinders farthest away with an excessively lean mixture, the carburetor would be set slightly rich. This, of course, is contrary to the EPA’s goals. The air injection into the exhaust manifold and the catalytic converter were stop-gap measures designed to compensate for the poor control the carburetor afforded.

Fuel injection was not new, but the new systems took advantage of the computer capabilities being designed into electronic ignition, and that is new. Diesel fuel injection has always been direct injection, in that fuel is injected directly into the combustion chamber. Introduction of fuel is what starts the combustion process in the diesel.

Early fuel injection systems began as “dribble” systems. Fuel was flowing constantly from the injectors, directed at the intake port for each cylinder. It would accumulate there until the intake valve for that cylinder opened and fuel and air were drawn into the cylinder. Timing of the injection was not deemed important like that of the diesel system. Rochester Division of General Motors manufactured this type of system beginning in the 1950s, and they were used on early Corvettes and some Pontiacs.

In general terms, the modern fuel injection system for the spark ignition engine consists of a series of injectors, one per cylinder, or a pair of injectors in the case of a throttle body system. Fuel is supplied to the injectors from a high pressure pump through a pressure regulator. With the regulator maintaining constant fuel pressure, the quantity of fuel delivered is controlled by the period of time the injector is open. The on-board computer reads the throttle position, engine RPM, engine load, inlet air flow, engine temperature and the signals from the oxygen sensors. With that information, it determines the period the injectors should be open. The oxygen sensor is a key component because it tells the computer how good a job it is doing at controlling the fuel mixture.

Under the relentless pressure to improve pollution control and fuel mileage, fuel injection progressed from injectors mounted in the intake manifold aimed at the intake valve. Direct injection, where fuel was injected into the combustion chamber similar to the diesel system, is the latest advancement. This new level of fuel control precision is making it possible to improve emission control and fuel mileage further.

Some of the systems today are capable of “learning.”  For example, if the vehicle owner were to change the air filtration system to a higher performance, less restrictive system, some of the computer systems are capable of adapting to the change in parameters. The next step will be controlling each cylinder individually.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.