Evaporative emission control system

The present invention broadly relates to fuel vapor recovery systems used in internal combustion engines, and deals more particularly with a system providing fuel tank isolation during purging of vapors from a carbon storage canister. An evaporative emission control system for an internal combustion engine isolates the fuel tank from the engine during purging of a carbon canister used to store fuel vapor drawn from the fuel tank during refueling. The flow of vapor from the tank to the canister is controlled by a main vapor control valve, and the flow of vapor from the canister to the engine is controlled by a purge valve. Pressure transducers are used to independently sense vapor pressure in the tank and in the canister. An electronic controller operates the valves based in part on the pressure information generated by the pressure transducers.