Evaporative Emissions System: Description and Operation

Fuel Vapor Canister And Purge Valve:

The Evaporative Emission Control System (EECS) used is charcoal canister storage. This method transfers fuel vapor from the fuel tank to an activated carbon storage canister to retain the vapors. When the engine is running, the fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process.

The purge valve is an integral part of the canister. When the engine is running, manifold vacuum is supplied to the top of the purge valve (control vacuum signal), which lifts the valve diaphragm and opens the valve. The lower tube on the purge valve (PCV tube) is connected to ported vacuum above the throttle valve. The rate of purge is controlled through this port by throttle position.

EVAPORATIVE CANISTER AND FILTER

The evaporative emission control canister contains activated carbon to retain fuel vapors transferred from the fuel tank. When the engine is running, the fuel vapor is purged from the carbon element and consumed in the normal combustion process. A filter element is located in the bottom of the canister.

FUEL FILLER CAP

The fuel tank filler neck is equipped with a screw-type cap. The threaded part of the cap requires several turns counterclockwise to remove it from the neck. The long threaded area is designed to allow any remaining fuel tank pressure to escape during the cap removal operation. A built-in ratchet-type torque-limiting device prevents any cap overtightening. To install the cap, rotate the cap clockwise until a clicking noise is heard. This means that the cap is fully seated with the correct torque.

PURGE CONTROL VALVE

The purge valve is an integral part of the canister. When the engine is running, manifold vacuum is supplied to the top of the purge valve (control vacuum signal), which lifts the valve diaphragm and opens the valve. The lower tube "ON" the purge valve (PCV tube) is connected to ported vacuum above the throttle valve. The rate of purge is controlled through this port by throttle position.

ROLLOVER VALVE

Fuel System Components:

The valve provides fuel leakage protection if the vehicle is accidently rolled over and also vents fuel vapors from tank to charcoal canister. The valve mounts in the vapor line.