Throttle Body Types

• Throttle bodies come in two basic types, either a standard throttle body or a throttle body injection unit. Standard throttle bodies don't carry fuel at all; they're just big butterfly valves that meter airflow into the intake manifold. Throttle body injection units look like carburetors, but use one or more injectors to shoot fuel down into the intake manifold.
  
  

Fuel Injector Function

• Regardless of where the injectors sit -- on top of the throttle body, in the intake manifold runners or in the top of the combustion chambers -- they all work the same way. A computer sends power to an electromagnet wrapped around a needle-valve in the injector. When the magnet energizes, the needle-valve pulls up and allows fuel to flow through the injector. The computer opens and closes the needle valve many times per second, allowing for precise control over fuel delivery.