The evaporative emission control system is designed to control the emission of gasoline vapors into the atmosphere.
On GLC and carbureted 323 models, the system consists of a charcoal canister, a check and cut valve, a liquid separator (wagon only), and purge control valves. On 626 models prior to 1988, the system consists of a charcoal canister, a check and cut valve (or three-way check valve), purge control valves, and on some early models, an evaporator shutter valve in the air cleaner.
On fuel injected 323s, as well as the 1988–89 626, MX-6 and 929, the system takes fuel vapor that is generated in the fuel tank and stores it in the charcoal canister when the engine is not running. This fuel vapor remains in the canister until the engine is started, at which time the fuel vapor is drawn into the intake manifold and burned. The system on these models is made up of the charcoal canister, purge control solenoid valves, a three-way check valve, a vacuum switch control valve and an electronic control unit.
When raw fuel evaporates, the vapors contain hydrocarbons. To prevent these vapors from escaping into the atmosphere, the fuel evaporative emission control system was developed. The 1979–80 RX-7 models use a ventilation and check valve and a charcoal canister located in the air cleaner. The 1981–85 RX-7 with carbureted engine is equipped with a conventional charcoal canister located beside the carburetor. On these models, the flow of vapor is controlled by a purge control valve located on top of the charcoal canister. On the 1984–89 RX-7 with fuel injection, evaporative fumes from the gas tank along with those from the canister are regulated by the purge control valve, which introduces them to the intake manifold. The purge control valve is located on the side of the oil filler pipe.
On 1979–80 RX-7 models, a ventilation and check valve prevents fuel vapors from reaching the atmosphere in the following manner: When the engine is off, the fuel vapor from the gasoline in the fuel tank is trapped in the fuel tank and evaporative line until it reaches a certain pressure. When that pressure is reached, the ventilation and check valve opens, allowing fuel vapors to pass into the rotor housings and oil pan, and mix with the blow-by gases trapped there. The trapped gases are then fed into the charcoal canister, along with vapors from the fuel in the carburetor float bowl. The fuel vapors remain in the canister until the engine is started, when manifold vacuum opens the check valve, allowing all of the vapors and blow-by gases in the rotor housings/oil pan and charcoal canister to flow into the intake manifold. There, the vapors and blow-by gases mix with the air/fuel mixture to be burned in the combustion chambers.
On 1981–89 RX-7 models, a check and cut valve prevents fuel vapors from reaching the atmosphere by performing the following functions: (1) When vapor pressure in the fuel tank becomes too great, the valve releases the pressure into the charcoal canister and rotor housings to prevent the tank from bursting; (2) When vacuum pressure in the tank becomes too high, the valve allows air into the tank to prevent it from collapsing and to insure that sufficient fuel is pumped to the carburetor or throttle body and not drawn back by the vacuum in the fuel tank; (3) When the vehicle is overturned, the valve prevents fuel from flowing out of the tank. On later models, when the engine is not running, vapors from the fuel tank are fed into the charcoal canister where they are trapped by the purge valve. When the engine is running with the throttle open, manifold vacuum opens the purge valve and the vapors trapped in the canister are allowed to flow out into the throttle and dynamic chamber. There, these vapors combine with the air/fuel mixture and pass through the intake manifold to be burned in the combustion chambers. The bottom of the canister contains an air filter on most models.