Abstract: An abnormality diagnosis apparatus for performing a leak check of an evaporative fuel processing system which includes a fuel tank, a canister for storing evaporative fuel generated in the fuel tank, a purging passage for connecting the canister to an intake system of an internal combustion engine, and a purge control valve provided in the purging passage. A process of reducing the pressure in the evaporative fuel processing system is executed with a limited flow rate of gases passing through the purge control valve when performing the leak check in an idling condition of the engine. The limited flow rate is set to a value equal to or smaller than a predetermined flow rate which is smaller than the maximum flow rate applied to the leak check performed in operating conditions other than the idling condition. The leak check is performed on the basis of a change in the pressure in the evaporative fuel processing system after the pressure reduction process.

Abstract: A highly stable engine failure diagnosing system free from influence of purging is presented. A monitoring apparatus for monitoring a fuel feed system of an internal combustion engine is provided with an A/F ratio detector and an A/F ratio controller for performing feedback control of the A/F ratio. An A/F ratio feedback coefficient is calculated according to the output of the detector. A malfunction determination parameter is calculated based on the coefficient. A purging is suspended when the parameter reaches a first decision value. The monitoring is suspended when the parameter reaches a second decision value in a purge cutting state. A value of the malfunction determination parameter it would take if the purge cut was not carried out is estimated using the value when the parameter reached the first decision value. The monitoring is resumed when the estimated value of the malfunction determination parameter reaches the second decision value.

Abstract: When a leakage fault occurs in the evaporated fuel processing system of a fuel tank, a control system reliably prevents leakage of the evaporated fuel from the point where the leakage fault has occurred. The fuel tank and a canister are connected to each other via a charge passage having a bypass valve, and the canister and an intake passage of an engine are connected to each other via a purge passage having a purge control valve. When a leakage fault occurs in the fuel tank (or the charge passage upstream of the bypass valve), the bypass valve and the purge control valve are opened and an atmosphere release control valve provided on the canister, is closed.

Abstract: A system for detecting malfunction of a radiator, more precisely a thermostat (shut-off valve) in the engine cooling system. In the system, an estimated coolant temperature CTW is calculated from the temperature condition and operating condition at engine starting. When the estimated coolant temperature CTW has reached a judge malfunction value CTWJUD but the detected coolant temperature TW has not reached a judge normal value TWJUD, the thermostat 64 is discriminated to have malfunctioned, thereby enabling to detect malfunction of the radiator with high accuracy and high response.

Abstract: There is provided an ignition timing control system for an internal combustion engine. An air-fuel ratio sensor is arranged in the exhaust system, for detecting the air-fuel ratio of exhaust gases emitted from a plurality of cylinders of the engine. The air-fuel ratio of a mixture supplied to each of the cylinders is estimated based on an output from the air-fuel ratio sensor, by using an observer for observing an internal operative state of the exhaust system based on a model representative of a behavior of the exhaust system. The ignition timing of the each cylinder of the engine is controlled based on the estimated air-fuel ratio of the mixture supplied to the each cylinder.