Evaporative Emissions System: Description and Operation

Fig. 455 - Evaporative Emission System:

This system, Fig. 455, reduces hydrocarbon emissions from the fuel system by the use of activated charcoal in the carbon canister. With engine off, fuel vapor from the fuel tank is led into the carbon canister for storage.

With engine running, the vapor is retained by the canister until it is purged by air drawn through the purge line into the intake manifold. As engine speed increases, the ported vacuum rises and opens the purge control valve, allowing vapor to flow through the purge line into the intake manifold.

When engine coolant temperature is lower than 122° F., the purge control valve is closed by the thermal vacuum valve, preventing vapor from entering the intake manifold.