Evaporative Emissions System: Description and Operation

Fig. 54 Evaporative Emission Control (EEC) system. Typical of General Motors vehicles:

This system, Fig. 54, allows evaporating fuel vapors to be stored for burning during combustion, rather than being vented to atmosphere when the engine is not running. This is accomplished by venting the fuel tank and usually the carburetor float bowl through a canister containing activated charcoal. The canister absorbs fuel vapors and retains them until it is purged or cleared by air drawn through a filter located either at the bottom of the canister or in the air cleaner snorkel. The canister absorbs fuel vapors when the engine is off. When the engine is running, vapors are drawn from the canister into the engine, where they are burned.