Abstract: A misfire state discrimination system of an internal combustion engine, which determines the occurrence of misfire under engine operating conditions that make misfire determination possible and counts the number of misfires to compare with a reference value. The misfire state of the engine is discriminated based on the result of comparison. In the system, when the engine operation moves from the conditions that makes the misfire determination possible, the count is saved and is counted up from the count when the engine operation returns to the condition. The saved count is also retained when the engine is stopped. Similarly, the number of combustion during which the determination of misfire occurrence is made is counted and the count is saved. This arrangement enables a rapid and accurate discrimination of the misfire state of the engine.

Abstract: A misfire state discrimination system of an internal combustion engine, which determines the occurrence of misfire under engine operating conditions that make misfire determination possible and counts the number of misfires to compare with a reference value. The misfire state of the engine is discriminated based on the result of comparison. In the system, when the engine operation moves from the conditions that makes the misfire determination possible, the count is saved and is counted up from the count when the engine operation returns to the condition. The saved count is also retained when the engine is stopped. Similarly, the number of combustion during which the determination of misfire occurrence is made is counted and the counted is saved. This arrangement enables a rapid and accurate discrimination of the misfire state of the engine.

Abstract: An evaporative fuel control system for an internal combustion engine having a throttle valve arranged in the intake system. A canister adsorbs evaporative fuel generated in the fuel tank. A purging passage extends between the canister and the intake system, for purging evaporative fuel into the intake system at a location downstream of the throttle valve, and a purge control valve is arranged across the purging passage, for controlling the flow rate of evaporative fuel supplied to the intake system through the purging passage. When the engine is in a predetermined operating condition, the flow rate of evaporative fuel supplied to the engine is changed by controlling the purge control valve, then the degree of influence of the evaporative fuel on an air-fuel ratio of a mixture supplied to the engine is detected before and after the changing of the flow rate of the evaporative fuel, and an operating error of the purge control valve is determined based on the detected degree of influence.

Abstract: A catalyst deterioration-detecting system for an internal combustion engine detects deterioration of a catalyst arranged in an exhaust passage of the engine based on the output from an oxygen concentration sensor arranged in the exhaust passage at a location downstream of the catalyst, during execution of air-fuel ratio control. The detection of deterioration of the catalyst is effected based on a value of a catalyst deterioration parameter indicative of a degree of deterioration of the catalyst, and an amount of variation in an air-fuel ratio control amount used in the air-fuel ratio control.

Abstract: An air-fuel ratio control system for an internal combustion engine comprises an exhaust gas component concentration sensor arranged in the exhaust system of the engine, for detecting concentration of oxygen present in exhaust gases emitted from the engine, and an ECU which controls the air-fuel ratio of an air-fuel mixture to be supplied to the engine, based on the difference between an output value from the exhaust gas component concentration sensor and a predetermined reference value, and detects deterioration of the exhaust gas component concentration sensor, based on the output value from the exhaust gas component concentration sensor. When the deterioration of the exhaust gas component concentration sensor is detected, a deterioration display signal is outputted, while whether execution of air-fuel ratio control is to be inhibited or to be continued is determined based on the deterioration degree of the exhaust gas component concentration sensor.

Abstract: An abnormality-detecting device for an exhaust gas component concentration sensor arranged in the exhaust system of an internal combustion engine detects abnormality of the exhaust gas component concentration sensor, based on an amount of change in an output from the exhaust gas component concentration sensor exhibited when a predetermined voltage is applied thereto. The abnormality-detecting device defers determination of abnormality of the exhaust gas component concentration sensor until the engine reaches a predetermined operating condition after the engine is started.

Abstract: An evaporative fuel-processing system for an internal combustion engine includes an evaporative emission control system comprising charging passage extending between the canister and a fuel tank, a purging passage extending between the canister and an engine intake system, an open-to-atmosphere passage communicating the interior of the canister to the atmosphere, a purge control valve for opening and closing the purging passage, and an open-to-atmosphere valve for selectively opening and closing the open-to-atmosphere passage. A tank internal pressure sensor detects pressure within the evaporative emission control system. An ECU introduces negative pressure from the engine intake system into the evaporative emission control system and the fuel tank by opening the purge control valve and closing the open-to-atmosphere valve.

Abstract: An oxygen sensor deterioration-detecting system for an internal combustion engine having a plurality of groups of cylinders groups, an exhaust system having a plurality of exhaust passages extending, respectively, from the cylinder groups, and catalytic converters arranged in the exhaust system, and a plurality of upstream oxygen sensors arranged, respectively, in the exhaust passages at locations upstream of the catalytic converters, includes a single downstream oxygen sensor arranged in a confluent portion of the exhaust passages at a location downstream of the catalytic converters, for detecting the mixed air-fuel ratio of exhaust gases emitted from the cylinder groups.

Abstract: An evaporative fuel-processing system for an internal combustion engine includes a charging passage extending between the canister and the fuel tank of the engine, a purging passage extending between the canister and the intake system of the engine, an open-to-atmosphere passage for communicating the interior of the canister to the atmosphere, a first control valve for selectively opening and closing the purging passage, and a second control valve for selectively opening and closing the open-to-atmosphere passage. A tank internal pressure sensor detects pressure within the evaporative fuel-processing system, and an ECU determines abnormality of the evaporative fuel-processing system, based on a variation in the detected pressure after the interior of the evaporative fuel-processing system is negatively pressurized into a predetermined negative pressure state.

Abstract: An evaporative emission control system includes a valve arranged in a passage communicating between a fuel tank and a canister. The valve opens the passage when pressure within part of the evaporative emission control system upstream of the valve exceeds a predetermined value and, closes the passage when the pressure is below the predetermined value. It is determined that the evaporative emission control system is normal when a value of the pressure with the part of the system detected by a pressure sensor is lower than a predetermined reference value below atmospheric pressure.

Abstract: The air-furl ratio of an air-fuel mixture supplied to an internal combustion engine is controlled in response to an output from at least one oxygen sensor arranged in an exhaust passage for detecting concentration of oxygen present in exhaust gases. The deterioration of the at least one oxygen sensor is detected based on the output therefrom. When the engine is detected to be in a predetermined abnormal operating state, it is not permitted to monitor the output from the oxygen sensor for detecting deterioration thereof.

Abstract: An evaporative fuel-processing system includes a first control valve arranged in a charging passage connecting between a fuel tank and a canister for adsorbing evaporative fuel generated from the fuel tank, a second control valve arranged in a purging passage connecting between the canister and an intake passage of the engine, a third control valve arranged in an air inlet port of the canister, and a system internal pressure sensor for detecting pressure within the system. The system is checked for a leak by monitoring a value of the pressure detected by the sensor after the system is negatively pressurized by closing the third control valve and opening the second control valve. The sensor is provided at a location upstream of the first control valve, and the first control valve is closed to detect a value of the pressure or a change thereof. Abnormality determination is carried out based on the detected value of the pressure.

Abstract: An air-fuel ratio control system for an internal combustion engine having a first and second groups of cylinders and first and second catalytic converters arranged respectively in first and second exhaust systems extending from the respective cylinder groups, includes first and second upstream oxygen sensors upstream of the catalytic converters, and a single downstream oxygen sensor downstream of the catalytic converters. The air-fuel ratios of air-fuel mixtures supplied into the first and second cylinder groups are controlled by the use of first and second air-fuel ratio control amounts based on outputs from the respective first and second upstream oxygen sensors and the downstream oxygen sensor, when the engine is in a predetermined operating condition.

Abstract: An air-fuel ratio control system for an internal combustion engine having a catalytic converter arranged in the exhaust system, and first and second air-fuel ratio sensors arranged upstream and downstream of the catalytic converter respectively has an ECU which calculates an air-fuel ratio correction amount, based at least on an output from the first air-fuel ratio sensor, and detects deterioration of the catalytic converter, based on an output from the second air-fuel ratio sensor when the engine is in a predetermined operating condition. The ECU inhibits detection of deterioration of the catalytic converter when the air-fuel ratio correction amount falls outside a predetermined range.

Abstract: A catalyst deterioration-detecting system is provided for an internal combustion engine having an oxygen concentration sensor arranged in an exhaust system downstream of a catalyst provided therein. An electronic control unit (ECU) controls the air-fuel ratio of a mixture supplied to the engine in response to an output from the oxygen concentration sensor. The ECU detects a value of an inversion period with which the output from the oxygen concentration sensor is inverted with respect to a predetermined reference value. Operating parameter sensors detect a value of at least one operating parameter of the engine related to a flow rate of the exhaust gases in the exhaust system. The ECU determines whether the catalyst is deteriorated, based on the detected value of the inversion period and the detected value of the at least one operating parameter. The ECU corrects the value of the inversion period in dependence on the detected value of the at least one operating parameter.

Abstract: An air-fuel ratio control system for an internal combustion engine calculates an air-fuel ratio feedback control parameter by proportional-integral control using a proportional factor and an integral factor, based an output signal from a second air-fuel ratio sensor arranged in an exhaust passage at a location upstream of a catalytic converter. An air-fuel ratio correction amount is calculated based on the air-fuel ratio feedback control parameter and an output signal from a first air-fuel ratio sensor arranged in the exhaust passage at a location upstream of the catalytic converter. An inversion period of the output signal from the second air-fuel ratio sensor is measured, and the proportional factor is changed according to the inversion period measured.

Abstract: An air-fuel ratio sensor deterioration-detecting device for an internal combustion engine having a catalytic converter arranged in the exhaust system, and first and second air-fuel ratio sensors arranged upstream and downstream of the catalytic converter respectively has an ECU which calculates an air-fuel ratio correction amount, based on outputs from the first air-fuel ratio sensors, and detects deterioration of the first air-fuel ratio sensor, based on the output from the first air-fuel ratio sensor. The ECU inhibits detection of deterioration of the first air-fuel ratio sensor when the air-fuel ratio correction amount falls outside a predetermined range.

Abstract: A catalyst deterioration-determining system determines deterioration of a catalyst arranged in the exhaust passage of an internal combustion engine. An ECU is responsive to an output from an O.sub.2 sensor arranged upstream of the catalyst or outputs from O.sub.2 sensors arranged upstream and downstream of the catalyst for controlling the air-fuel ratio of a mixture supplied to the engine by means of an air-fuel ratio correction value (first air-fuel ratio control). When the engine is in a predetermined operating condition, the system effects changeover from the first air-fuel ratio control to a second air-fuel ratio control which is responsive to the output from the downstream O.sub.2 sensor for controlling the air-fuel ratio of the mixture by means of the air-fuel ratio correction value.

Abstract: An abnormality detection system is provided, which detects abnormality in an evaporative fuel control system for an internal combustion engine. A plurality of temperature sensors are arranged in an evaporative fuel storage device at different locations for detecting the temperature of an adsorbent or in the vicinity thereof within the storage device at the different locations. An ECU controls at least one of charging of evaporative fuel from the fuel tank to the storage device and purging of evaporative fuel from the storage device to the intake system of the engine. The ECU determines the presence or absence of an abnormality in the evaporative fuel control system, based upon output values from the temperature sensors assumed when the control system is operative. A state in which adsorption of evaporative fuel generated in the fuel tank to the adsorbent of the storage device has been completed is detected, based upon the amount of a rise in temperature detected while the charging is being effected.

Abstract: A method of controlling exhaust gas recirculation for an internal combustion engine having an exhaust gas recirculation control system comprises the step of determining that there is failure in the exhaust gas recirculation control system when a difference between an actual value of valve opening of an exhaust gas recirculation valve of the system arranged in an exhaust gas recirculation passage for controlling an amount of exhaust gases returned from an exhaust passage to an intake passage of the engine and a desired value of the valve opening of the exhaust gas recirculation valve is equal to or larger than a predetermined value which is dependent on operating conditions of the engine.