Abstract: Fuel vapor is produced in a fuel tank and absorbed in a canister. The absorbed fuel vapor is purged through a purge passage into an engine induction passage under predetermined engine operating conditions. A purge valve is provided in the purge passage to regulate the supply of gaseous mixture, including the absorbed fuel vapor, into the engine. A purge rate factor is determined corresponding to the concentration of evaporated fuel in the gaseous mixture. The concentration is determined utilizing the temperature of the fuel in the fuel tank.

Abstract: A determination is made as to whether or not a fuel tank for an engine or the like is being replenished with fuel. The temperature of the fuel in the fuel tank is detected, and if the fuel temperature is dropping a determination of fuel tank replenishment is arrived at. Desirably, it is determined that the fuel tank is being replenished, if fuel temperature dropping has occurred for a predetermined number of times over a predetermined time period. Further, by using such a detecting device in a breakdown diagnosis device for an evaporated fuel processing mechanism which diagnoses whether or not fuel leakage is taking place in a predetermined section of a flow path from the fuel tank to an intake passage of an automobile engine erroneous diagnosis is prevented by preventing diagnosis during fuel tank replenishment.

Abstract: Fuel vapor is produced in a fuel tank and absorbed in a canister. The absorbed fuel vapor is purged through a purge passage into an engine induction passage under predetermined engine operating conditions. The air/fuel ratio is learned for air/fuel ratio feedback control. The learning control is inhibited when the fuel temperature exceeds a reference value during the air/fuel ratio feedback control. In another aspect of the invention, a purge valve is provided in the purge passage. The air/fuel ratio correction factor is set at an initial value in response to a movement of a purge valve from its open position toward its closed position.

Abstract: A function diagnosing apparatus of an evaporative emission control system for an automotive vehicle executes a diagnosis when a diagnosis starting condition is satisfied. First, a purge cut valve and a vent cut valve are closed, and a bypass valve for a one way valve disposed between a fuel tank and a canister is opened. When a pressure in a purging line is not raised up by these valve operations, it is decided that the system goes wrong due to one of of the bypass valve in a cold condition, fuel vapor leakage, of the vent cut valve in an open condition, and/or no vapor existence. Upon opening the vent cut valve, it is decided as to whether the purge line pressure is dropped or not. When the purge line pressure is dropped, it is decided that the vent cut valve is normal. When the purge line pressure is not dropped, it is decided that vent cut valve is sticking closed.

Abstract: A leak diagnosis system for an evaporative emission control system executes a correction process of diagnosis decision value. When the purge control of the evaporative emission control system is not executed, a purging line of the system is set in the atmospheric condition for a predetermined time. A pressure sensor installed in the purging line detects a pressure value V.sub.A0 in the atmospheric condition. A control unit of the leak diagnosis system determines a leak decision value V.sub.P0 on the basis of the atmospheric pressure detection value and an equation V.sub.P0 =V.sub.A0 +.DELTA.V.sub.0 where .DELTA.V.sub.0 is a difference between the output value in the predetermined positive pressure P.sub.0 and the output value V.sub.A0 in the atmospheric pressure condition and is constant. Therefore, it becomes possible to accurately execute the leak diagnosis.

Abstract: Fuel vapor is produced in a fuel tank and absorbed in a canister. The absorbed fuel vapor is purged through a purge passage into an engine induction passage under predetermined engine operating conditions. The air/fuel ratio is learned for air/fuel ratio feedback control. The learning control is inhibited when the fuel temperature exceeds a reference value during the air/fuel ratio feedback control. In another aspect of the invention, a purge valve is provided in the purge passage. The air/fuel ratio correction factor is set at an initial value in response to a movement of a purge valve from its open position toward its closed position.

Abstract: Fuel vapor is produced in a fuel tank and absorbed in a canister. The absorbed fuel vapor is purged through a purge passage into an engine induction passage under predetermined engine operating conditions. The air/fuel ratio is learned for air/fuel ratio feedback control. The learning control is inhibited when the fuel temperature exceeds a reference value during the air/fuel ratio feedback control. In another aspect of the invention, a purge valve is provided in the purge passage. The air/fuel ratio correction factor is set at an initial value in response to a movement of a purge valve from its open position toward its closed position.

Abstract: A vehicle engine temperature is detected, and a radiator fan fault warning is given so as to prevent engine overheating when this temperature rises to or above a preset determining value under a predetermined test conditions. Preferably, it is determined that the radiator fan has a fault when a temperature equal to or above this determining value holds for at least a predetermined time. More preferably, this determining value is set low while the vehicle is in motion. By providing these supplementary conditions, incorrect diagnosis of a fault in the radiator fan is prevented.

Abstract: An apparatus and method for determining an engine operation control based engine revolution displacement for a multi-cylinder four-stroke internal combustion engine are disclosed in which a reference crank angle sensor is disposed on an engine crankshaft so as to output a reference signal which corresponds to a predetermined crank angular position with respect to a top dead center of each cylinder whenever the engine has revolved through a set crank angular displacement according to the number of cylinders (720.degree./6=120.degree., in the case of a six-cylinder engine). A unit crank angle sensor is disposed on the engine crankshaft so as to output a unit angle (1.degree. or 2.degree.

Abstract: A first passage provided with a first valve for guiding vaporized fuel from a fuel tank into a canister, and a second passage provided with a second valve connecting this canister with an intake pipe downstream or a throttle, are provided. A pressure detecting mechanism is provided between this first valve and second valve, and a third valve is provided for leading fresh air into the canister. When the engine running condition satisfies a predetermined positive pressure test condition, the second and third valves are closed and the first valve is opened. In this state, the presence or absence of a leak is determined from the pressure detected by the pressure detecting mechanism. In other words, it is determined for example that the fuel tank has no leak if the pressure rises above a predetermined value.