Evaporative Emissions System: Operation: Tercel
The fuel evaporation system is controlled by a thermal vacuum switching valve (TVSV), outer vent control valve and a vacuum control valve (VCV). When engine is not running, outer vent control valve is open. This allows fuel vapors from carburetor float chamber to be absorbed in charcoal canister.
When engine is running, the TVSV opens and causes vacuum to build at the VCV. When engine warms up, the VCV opens and allows purging of stored fuel vapors in charcoal canister to intake manifold.
The system also uses 3 check valves in charcoal canister. These control fuel tank pressure and vent excess vacuum from tank.