Firebird V8-305 5.0L (1982)
Evaporative Emission Control Canister: Description and Operation
Vent and Purge Valve Type
Fig. 74 Vent & Purge Valve Type Vapor Storage Canister
This canister is equipped with both a vent valve and a canister purge valve. The rate at which fuel vapor is drawn into the engine is controlled by a
Thermal Vacuum witch (TVS), which supplies ported vacuum to the purge valve when engine coolant temperature is above a pre-determined
value.
With engine idling at normal operating temperature, the purge valve is forced closed by spring tension and no purging of the canister occurs.
NOTE: On some models, a small amount of fuel vapor is drawn from the canister through a bleed hole, allowing some canister purge through the PCV
system at idle.
When the carburetor throttle plates are opened, the signal port located above the throttle plates is uncovered and a ported vacuum signal is applied
to the purge valve. Vacuum then overcomes spring tension, opening the valve and allowing vapors to be drawn into the engine for burning.
