Emission Control Systems: Description and Operation

The emissions control system consists of devices to control tailpipe emissions as well as hydrocarbons produced by evaporating fuel.
The primary emission control system is the Bosch Digital Motronic Engine (DME) control system. It offers more precise fuel and ignition control over a wider range of conditions than can be achieved with a carburetor or mechanical injection system. The use of an exhaust gas oxygen sensor, and various engine sensors allows the injection and ignition systems to compensate for changes in atmospheric conditions (temperature, altitude, etc.) as well as mechanical conditions (such as state of tune, etc.) allowing the catalytic converter to operate at peak efficiency.
To prevent the introduction of leaded fuel to the system, a fillpipe restrictor is installed. This prevents the larger diameter fuel nozzles used for leaded fuels from entering the fillpipe. Leaded fuel will permanently contaminate the oxygen sensor, and the catalytic converter.
The emissions created by the evaporation of raw fuel are controlled by the use of a closed ventilation system for the fuel tank and an activated charcoal canister to capture the fuel vapors. The charcoal canister captures and stores the vapors as they expand. When the engine is started, the purge control valve opens allowing the engine to draw vapors through the charcoal canister and burning the stored fuel vapors.