Abstract: A method is provided for controlling an engine in a vehicle to facilitate determination of engine position sensor correction factors. The vehicle includes a motor, which is operatively connected to the engine, a sensor configured to detect engine position, and a controller, which is in communication with the engine, the sensor and the motor. It is determined when an engine shutdown is requested, for example, when the controller commands the vehicle to be powered by the motor. It is next determined whether engine position sensor correction factors are known. If they are, the engine control routine is stopped. If the correction factors are not known, fuel to the engine is discontinued, and the motor is employed to spin the engine at an approximately constant speed. The engine position sensor correction factors can then be determined while the engine is rotating in a defueled state.

Abstract: A method is presented for controlling fuel tank pressure in an internal combustion engine. The engine, the fuel tank and the carbon canister are connected in a three-way connection. The engine can be selectively isolated by a purge control valve, and the fuel tank can be selectively isolated by a fuel tank control valve. The operation of both valves is coordinated by an electronic engine controller. By isolating the fuel tank during the carbon canister purge, better estimate of the fuel fraction flowing into the engine can be achieved, thereby improving fuel economy.

Abstract: A method is presented for controlling fuel tank pressure in an internal combustion engine. The engine, the fuel tank and the carbon canister are connected in a three-way connection. The engine can be selectively isolated by a purge control valve, and the fuel tank can be selectively isolated by a fuel tank control valve. The operation of both valves is coordinated by an electronic engine controller. By isolating the fuel tank during the carbon canister purge, vapor spikes into the engine are eliminated, thus preventing engine stalls. Also, canister durability is improved by continuously storing and purging vapors in opposite directions.

Abstract: A method is presented for diagnosing a condition in the fuel vapor purge system. The engine, the fuel tank and the carbon canister are connected in a three-way connection. The engine can be selectively isolated by a purge control valve, and the fuel tank can be selectively isolated by a fuel tank control valve. The operation of both valves is coordinated by an electronic engine controller. By isolating the fuel tank, and comparing the actual rate of change of the internal tank pressure (from the tank pressure sensor) to the estimated rate of change (from engine operating conditions) it is possible to determine if a condition occurred, and whether it is in the tank or in the vapor purge lines.