Abstract: A fuel-vapor-processing system for an engine has a canister for accumulating fuel evaporation gas. The system has a leak-check apparatus for checking a leak on passages. The leak-check apparatus includes a leak-check means for carrying out leak-check processing when the engine if in a stopped state. The leak-check means operates only if a predetermined condition is satisfied. It is thus possible to reduce the number of times the leak-check processing is carried out and, hence, possible to reduce power consumption. For example, only if a relatively small leak is detected when the engine is in a running state, the leak-check processing is carried out in a stopped state to verify existence of such a leak. In the leak-check processing, the temperature of fuel, detected by a sensor or an estimated value, may be taken into consideration.

Abstract: A fuel evaporation control system is connected to an engine control system in which an air-fuel ratio in mixture gas supplied to an engine is controlled to an optimum level. Fuel evaporated from a fuel tank is absorbed by a canister, and the absorbed fuel is purged into the engine. Deterioration of the canister in its air-permeability is detected based on measured pressure in the fuel evaporation control system or calculated density in the purge gas, both the pressure and the density being measured or calculated under two different amounts of purge gas flow. Deterioration of the canister in its fuel-absorbing ability is also detected based on the purge gas density.

Abstract: Even after initiation of a fuel cutting operation, an estimated coolant temperature value is continuously renewed based on an engine operating state until a predetermined time period elapses. Thus, an increase in the coolant temperature during the fuel cutting operation can be estimated. Furthermore, overestimation of the increase in the coolant temperature during the fuel cutting operation can be avoided since the renewal of the estimated coolant temperature after the elapse of the predetermined time period is prohibited. In this way, possible deterioration of coolant temperature estimation accuracy caused by the fuel cutting operation can be minimized, allowing more accurate coolant temperature estimation. As a result, when abnormality of a thermostat is judged based on a difference between an actual coolant temperature and the estimated coolant temperature value, misjudgment of a normal thermostat as an abnormal thermostat can be prevented.

Abstract: A malfunction of a thermostat in a coolant circulating path is detected from an engine side coolant temperature in consideration of the following behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes different considerably from that in the normal time in the temperature range in which the thermostat is to be normally closed. When a closure-malfunction occurs, the coolant temperature becomes different considerably from that during the normal time in the temperature range in which the thermostat is to be normally opened. Alternatively, the malfunction may be detected from a difference between the engine side coolant temperature and a radiator side coolant temperature.

Abstract: In a diagnosis apparatus, when tank internal pressure does not decrease up to a given negative pressure at a time when a given time has lapsed after starting negative pressure introduction into an evaporation gas purge system line, it is determined that the purge system line is abnormal and the abnormal cause is determined based on the internal pressure change amount &Dgr; P. The diagnosis apparatus identifies a valve opening state locking of an atmosphere change over valve, if &Dgr; P>K2, a valve closing state locking of a purge control valve, if &Dgr; P≦K2, and a large amount of leakage, if K1<&Dgr; P≦K2. The internal pressure change amount &Dgr; P is detected during a normal driving operation, at which the purge control valve is intermittently driven to intermittently purge the evaporation gas in a state that the atmosphere change over valve is opened.

Abstract: A thermostat malfunction detecting system is provided for detecting a malfunction of a thermostat in a coolant circulating path based on an engine side coolant temperature. When an open-malfunction of the thermostat occurs, the coolant temperature becomes considerably different from that normally expected for times at which the thermostat is expected to be closed. When a closure-malfunction occurs, the coolant temperature becomes considerably different from that normally expected for times that which the thermostat is expected to be opened. As an alternative, the malfunction may be detected from the difference from the engine side coolant temperature and the radiator side coolant temperature.

Abstract: Malfunction of an engine coolant thermostat is detected from the engine side coolant temperature by the subsequent behavior of the coolant temperature. When an open-malfunction occurs, the coolant temperature becomes considerably different from that normally expected for times at which the thermostat is expected to be closed. When a closure-malfunction occurs, the coolant temperature becomes considerably different from that normally expected for times at which the thermostat is expected to be opened. Alternatively, the malfunction may be detected from the difference between the engine side coolant temperature and the radiator side coolant temperature.

Abstract: A leakage diagnosing apparatus for an evaporated gas purge system, which executes purge system leakage diagnosis based on a detected pressure change amount and an introduced pressure which is introduced into a part of the purge system including at least a fuel tank and a canister. The detected pressure change amount is obtained by detecting pressure in the part of the purge system after such part of the purge system is hermetically sealed. Accordingly, the reliability of the leakage diagnosis is improved because an erroneous diagnosis caused by the introduced pressure is prevented. The detected pressure change amount may be compensated based on the introduced pressure into the sealed gas purge system. Accordingly, an erroneous leakage determination is prevented, and the reliability of leakage determination is improved.

Abstract: A valve timing control apparatus for an internal combustion engine includes a variable valve timing control mechanism of a hydraulic type which is provided in a drive force transmission arrangement for transmitting a drive force from a driving shaft to a driven shaft for actuating one of an engine-cylinder inlet valve and an engine-cylinder outlet valve, and which can relatively rotate one of the driving shaft and the driven shaft in a predetermined angular range. A detecting device operates for detecting a condition in which air enters hydraulic working fluid in the variable valve timing control mechanism. A trouble diagnosis device operates for implementing a trouble diagnosis on the variable valve timing control mechanism. An inhibiting device operates for inhibiting the trouble diagnosis implemented by the trouble diagnosis device when the detecting device detects the condition in which air enters hydraulic working fluid in the variable valve timing control mechanism.

Abstract: When a diagnosis execution condition is established, a canister closure valve is closed, thereafter, a purge control valve is opened, a purge control valve is closed in a state where negative pressure is introduced into an evaporated gas system to thereby maintain the evaporated gas system in a hermetically-sealed state and the hermetically-sealed state is continued until abnormality diagnosis is finished. Time period for maintaining the evaporated gas system in the hermetically-sealed state is divided into three time periods of a pressure change determining time period at a first time, an awaiting time period and a pressure change determining time period at a second time.

Abstract: A valve timing control apparatus for an internal combustion engine includes a variable valve timing control mechanism of a hydraulic type which is provided in a drive force transmission arrangement for transmitting a drive force from a driving shaft to a driven shaft for actuating one of an engine-cylinder inlet valve and an engine-cylinder outlet valve, and which can relatively rotate one of the driving shaft and the driven shaft in a predetermined angular range. A detecting device operates for detecting a condition in which air enters hydraulic working fluid in the variable valve timing control mechanism. A trouble diagnosis device operates for implementing a trouble diagnosis on the variable valve timing control mechanism. An inhibiting device operates for inhibiting the trouble diagnosis implemented by the trouble diagnosis device when the detecting device detects the condition in which air enters hydraulic working fluid in the variable valve timing control mechanism.

Abstract: In a misfire detecting apparatus of an internal combustion engine, a difference in rotational-speed variance from a rotation signal NE of a crankshaft and the difference in rotational-speed variance is compared with a predetermined misfire criterion value in order to make a determination as to whether a misfire has occurred in the internal combustion engine. The misfire detecting apparatus is applied to a six-cylinder internal combustion engine. An ECU employed in the misfire detecting apparatus is used for calculating differences in rotational-speed variance by using a 720.degree. CA, a 360.degree. CA, and a 120.degree. CA differential techniques. The differences in rotational-speed variance computed by using the differential techniques are each compared with a respective predetermined misfire criterion value. An outcome of the comparison is used for updating a misfire count.

Abstract: An apparatus for detecting a misfire in an internal combustion engine for a vehicle includes a rotational speed change quantity computing unit which detects a rotational speed of the engine and computes a change quantity of the rotational speed of the engine, a misfire determination value correction coefficient setting unit which detects a load on the engine and sets a correction coefficient of a misfire determination value based on a result of detection of the engine load, a misfire determination value setting unit for setting a misfire determination value based on the set misfire determination value correction coefficient, and a misfire determining unit for determining whether a misfire has occurred in the engine by comparing the change quantity of the rotational speed of the engine from the rotational speed change quantity computing unit with the misfire determination value from the misfire determination value setting unit.