Evaporative Emissions System: Operation

Fuel vapor is stored in expansion chamber in fuel tank, and in vapor line up to one-way check valve. When vapor pressure becomes higher than set pressure of one-way valve, valve opens allowing vapor into charcoal canister. While engine is stopped or idling, idle cut-off valve is closed and vapor is absorbed by charcoal. At partially opened throttle, idle cut-off valve is opened by manifold vacuum. Vapor, stored in charcoal canister and vapor line, is then purged into intake manifold and burned in the engine. In addition, any excessive pressure or vacuum which might build up in fuel tank is relieved by two-way valve in fuel filler cap.