Evaporative Emissions System: Description and Operation

Fig. 32 - Evaporative Emission Control System:

Fig. 33 - Evaporative Emission Control System:

The evaporative emission system, Figs. 32 and 33, is used to prevent the emission of gasoline vapors, generated by the ambient temperature, into the atmosphere. The system consists of a fuel tank, condenser tank, check valve, an oil separator on 1972 models and a carbon canister on 1973-82 models.

When the engine is not running, the fuel vapor in the fuel tank is channeled to the condenser tank. The fuel returns to the tank as the ambient temperature changes and the fuel vapor is condensed. During engine operation, the fuel vapor that has not condensed is routed to the carbon canister on 1973-82 models. On 1973-82 models, the fuel vapor in the canister is absorbed by the carbon and is stored. The stored vapor is removed from the carbon by fresh air passing through the inlet hole in the bottom of the canister. The vapor is then passed into the air cleaner and to the combustion chamber.

On 1973-82 models, the check valve or fuel vapor valve, located between the condenser tank and the carbon canister, permits fuel vapor and ventilation to flow during normal operation. If the vapor line between the check valve and canister becomes clogged, ventilation of the fuel system does not occur and fuel supply to the engine is cut off. When the fuel vapor in the fuel tank is expanded due to intense heat, the pressure in the tank increases. To prevent this increase in pressure, the check valve opens to release the pressure to the atmosphere.

1980 California and 1981-82 all, incorporate a water thermo valve and a purge control valve, Fig. 34. During engine warm-up when engine coolant temperature is low, the fuel vapors from the tank are stored in the carbon canister. After the engine warms up, the water thermo valve opens and the intake manifold vacuum actuates the purge control valve. When the purge control valve is actuated, the fuel vapor stored in the canister is purged by drawing fresh air through the inlet hole in the bottom of the canister and drawn into the intake manifold.

On 1980 2.3L California models and 1981-82 all, an evaporative shutter valve is installed in the air cleaner inlet pipe and controlled by intake manifold vacuum. When the engine is stopped, the evaporative shutter shuts the air cleaner inlet pipe causing fuel vapor created in the carburetor to be stored in the canister instead of being released to the atmosphere. Intake manifold vacuum holds the evaporative shutter open during engine operation.