Evaporative Emissions System: Description and Operation

Evaporative Emission Control System:

The evaporative emission control system (EECS) is the charcoal canister storage type. Fuel vapors from the tank are transferred to and stored in the canister when the vehicle is not running. When the engine is running, fuel vapors are purged from the carbon element by intake air flow and consumed in the normal combustion process. Poor idle, stalling, driveability problems and fuel odors can all result from EECS malfunctions.

Canister and Purge Valve:

PURGE VALVE

The purge valve is an integral part of the canister. When the engine is running, vacuum (control vacuum signal) is supplied to the top of the purge valve to lift the valve diaphragm and open the valve. The lower tube on the purge valve is connected to manifold vacuum on the throttle body.
The control valve only opens when sufficient vacuum is applied, thus preventing purge under conditions of low ported vacuum.

Fuel Filler Cap:

FUEL FILLER CAP

The fuel filler cap has both a vacuum valve and a pressure valve. If a vacuum develops in the fuel tank, the ambient valve of the cap will open and air will flow into the tank through the vacuum valve.
If pressure in the tank exceeds a specific value, the pressure valve will open and fuel vapor will be vented to the atmosphere. This valve does not function under normal operating conditions.