With Tank Pressure Control Solenoid Vacuum Valve

The evaporative emission control system used in this vehicle consists of those parts as shown in figure above. When the pressure of the vapor generated in the fuel tank increases higher than specified pressure, it pushes open the tank pressure control valve and enters EVAP canister. However, under the conditions that the engine is running, the fuel level is lower than the specified level, possibility of the fuel liquid flowing into the vapor line is little, tank pressure control solenoid vacuum valve is turned ON by ECM and vacuum is applied to the diaphragm of tank pressure control valve. Thus, the vapor passage of tank pressure control valve opens to allow continuity between the fuel tank and EVAP canister. As a result, under above conditions, the vapor in the fuel tank flows into EVAP canister without being stopped by tank pressure control valve. ECM controls EVAP canister purge valve in following ways according to signals from various sensors.
1. When the engine coolant temperature is 80°C or higher and the A/F is being fed back, ECM controls ON/OFF (open/close) switching of EVAP canister purge valve at a constant rate of 10 times/second and the length of its ON time depending on following factors so as to prevent the A/F from being changed suddenly.
- Engine speed
- Manifold absolute pressure
- Concentration of fuel vapor in purge line (fuel vapor concentration is calculated based on how much the feed back A/F changes when the flow rate in the purge line is changed). Also, when the vapor concentration is lower than the specified value, ECM stops operation of the EVAP canister purge valve for a specified time.
2. When the engine is running under higher load conditions and/or at a higher speed than specified values, ECM keeps the EVAP canister purge valve open as long as such driving conditions continue.
3. ECM keeps the EVAP canister purge valve closed when neither of above "1" and "2" applies. When the EVAP canister purge valve opens, fuel vapor in the EVAP canister is sucked into intake manifold. At this time, EVAP canister is purged or cleaned by the air drawn through the air pipe.