by Keith Hamburger

Created on: April 10, 2008

Fuel injectors are high precision electro-mechanical devices that spray fuel into your engine. While fuel injectors have been around for a very long time, they are essential for a diesel engine to work, until about thirty years ago they were fairly uncommon on gasoline engines. Years ago only the most exotic performance cars used fuel injectors on gasoline engines. Today, however, they have replaced carburetors on virtually all cars. The precise control of fuel mixtures allowed by injection systems is essential to the fuel economy and emissions control expected of today's drivers.

There are two types of fuel injection systems.

Throttle-body systems are a direct replacement for carburetors. Sitting on top of the intake manifold a throttle-body injection system (TBI) has one or two injectors that spray a steady stream of fuel into the air flowing through the breather. As you press on the throttle pedal the throttle opens underneath the injectors and the fuel spray is increased to provide more power. When you release the pedal the throttle closes and the fuel flow is decreased for less power. This system is uncommon on newer cars.

Multi-port injection systems (MPI) have several fuel injectors, one or more for each cylinder. These systems have various mechanisms for timing when they spray the fuel but, generally, they inject fuel into the cylinder timed with the intake or ignition stroke of the engine. MPI systems can be located on the intake manifold just before the intake valve or may spray fuel directly into the cylinder. In either case, the air coming through the breather goes through a throttle on top of the intake manifold. The throttle is controlled by the throttle pedal, as in the TBI system, but the fuel isn't injected until after the air has passed through the throttle. MPI is the most common form of fuel injection system on today's cars.

There are a number of symptoms of dirty or clogged fuel injectors. Since almost all fuel injected vehicles are computer controlled you may get errors from the computer and the check engine light may come on. A fuel injector problem may show an error of a misfire. This misfire is called a "lean misfire" because the fuel injector isn't putting enough fuel into the cylinder, the cylinder is running lean. Since the fuel isn't burning with the air in the cylinder you may also get an error from the oxygen sensor. Even if you don't have an error on the computer you may notice other problems such as a rough idle, loss of power

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