Fuel Evaporation System: Description

The fuel evaporation system is designed to prevent the escape of raw fuel vapor into the atmosphere. Components include a sealed fuel tank with integral expansion chamber, vacuum relief filler cap, charcoal canister(s) with 2 or 3 integral check valves, bi-metallic vacuum switching valve (Camry, Celica, fuel injected Corolla, Cressida, Land Cruiser, MR2, and Supra), restrictor (Celica GT-S manual transaxle).

Carbureted Corolla, Pickup, 4Runner and all Tercel models also use an outer vent control valve, vacuum switching valve, emission computer and temperature switch. Additional components include a throttle position switch (carbureted Corolla), vapor separator (Land Cruiser and Tercel), vacuum control valve (Land Cruiser), vacuum switch (Tercel), speed sensor (carbureted Pickup and 4Runner) and check valve (Van). All models use connecting lines and hoses.

When fuel vapor pressure builds in tank, a check valve in canister opens and vapor flows into canister for storage. When vacuum forms in tank, a check valve in canister opens and stored vapor is drawn into fuel tank. If fuel tank vacuum should increase above a preset level, a vacuum relief valve opens in filler cap and fresh air flows into fuel tank to prevent tank collapse.