Fuel System

To run smoothly and produce power most efficiently, the engine requires the proper mixture of air and fuel-the proper air/fuel ratio. Depending on conditions, the optimum ratio for gasoline-fueled engines is about 15:1, fifteen parts of air for every one part of fuel. The throttle controls the amount of air entering the engine. The fuel system's job is to deliver and disperse fuel in the proper ratio to the incoming air.

Traditionally, the job of fuel delivery has been handled by a carburetor, a device carefully calibrated to dispense and atomize fuel in proportion to the amount of air passing through it. To meet the increasing demand for performance with economy and reduced exhaust emissions, many modern engines, including the Volkswagen engines covered in this manual, use a more sophisticated fuel injection system. It measures the incoming air more precisely, and in turn meters fuel more precisely for better control of the air/fuel ratio. This precise control means greater efficiency over a wider variety of operating conditions. In spite of all this sophistication, the fundamental-task of the fuel injection system is still simply to control the ratio of fuel and air entering the engine's combustion chambers.

The fuel system of the automobile also includes a fuel storage, the fuel tank, and a network of pump and lines to transfer the fuel from the tank to the injection system.

A diesel engine's fuel system operates differently. It is free to intake as much air as it needs. The accelerator pedal controls the amount of fuel injected into the cylinders.