Except California Emission Vehicle With A/T

An evaporative emission control system is used to prevent emission of fuel vapor.
The vapor generated in the fuel tank while driving or the engine at a stop passes through a tank pressure control valve and enters the EVAP canister where the charcoal absorbs and stores the fuel vapor.
The EVAP canister purge valve is controlled by ECM according to signals from various sensors. When none of the following conditions exists, ECM controls ON/OFF (open/close) switching of the purge valve at a constant rate (10 times per second) and its opening (amount of purge air) by increasing and decreasing its ON time.
- When idle switch turns ON.
- When engine coolant temp. is low.
- When engine speed is low.
- When vehicle is stopped.
The higher the engine speed rises and the more fuel mixture is drawn in, the larger amount of air is purged.
When the purge valve opens, fuel vapor in the canister is sucked into intake manifold.
In this state, the canister is purged or cleaned by air drawn through the filter at the bottom of the canister.
The tank pressure control valve is provided to keep the pressure in the fuel tank constant. When the pressure in the fuel tank becomes positive and reaches its specified value, it opens the valve to let the vapor flow into the EVAP canister. On the other hand, when the pressure in the fuel tank becomes negative and reaches its specified value, it opens the valve to let the air flow into the fuel tank.
ECM also checks if the EVAP canister purge flow occurs when the EVAP purge duty (purge volume) is changed while the engine is running at the idle speed by checking the amount of variation in the idle air control duty and the fuel injection time.