Evaporative Emissions System: Description and Operation

Fig. 8 Evaporative Emission Control:

This system, Fig. 8, prevents fuel vapors from being released into the atmosphere. With this system, fuel vapors are trapped and directed to the engine for burning during engine operation. Fuel vapors from the fuel tank are vented through a rollover vent valve in the vapor line to the charcoal canister. This valve prevents the possibility of raw fuel from being drawn into the charcoal canister and also prevents fuel loss if the vehicle overturns.
The Electronic Control Assembly (ECA), used to control fuel injection, is also used to control this system. The ECA determines the engine operating condition from various sensors and switches and will activate numbers 1 and 2 solenoid valves when the following conditions exist. When the underhood temperature and engine coolant temperature are both above 122°F, the number 1 solenoid valve opens and allows the canister to purge through the number 1 purge control valve. When engine speed is above 1500 RPM at wide open throttle, the number 2 solenoid valve is also opened to allow additional canister purging through the number 3 purge control valve.