Abstract: A method for determining the effectiveness of a catalyst to remove emissions from the exhaust of an internal combustion engine. The method includes measuring an upstream time history of a signal produced by an exhaust gas oxygen sensor upstream of the converter and a time history of an exhaust gas oxygen sensor disposed downstream of the converter. The time histories vary between a lean air-fuel ratio signal level and a rich air-fuel ratio signal level. A time delay is determined between the upstream time history and the downstream time history during transitions in such time histories from the lean air-fuel ratio signal level to the rich air-fuel ratio signal level. The determined time delay is compared with a reference time delay to determine the efficiency of the converter. The converter is determined to be ineffective if the converter as been determined to be potentially ineffective and the time delay is determined to be less than the reference time delay.

Abstract: A method for determining the effectiveness of a catalyst to remove emissions from the exhaust of an internal combustion engine. The method includes measuring an upstream time history of a signal produced by an exhaust gas oxygen sensor upstream of the converter and a time history of an exhaust gas oxygen sensor disposed downstream of the converter. The time histories vary between a lean air-fuel ratio signal level and a rich air-fuel ratio signal level. A time delay is determined between the upstream time history and the downstream time history during transitions in such time histories from the lean air-fuel ratio signal level to the rich air-fuel ratio signal level. The determined time delay is compared with a reference time delay to determine the efficiency of the converter. The converter is determined to be ineffective if the converter as been determined to be potentially ineffective and the time delay is determined to be less than the reference time delay.

Abstract: A method and system for estimating the midbed temperature of a catalytic converter in an exhaust system of an internal combustion engine. A rate of change in the speed of the engine is sensed and an estimated number of misfires occurring in the engine over a predetermined number of cylinder filling events is determined based on the sensed rate of change in engine speed. An instantaneous temperature of exhaust gas at the exhaust flange is determined based on the estimated rate of misfires. An instantaneous temperature at the midbed point of the catalytic converter is then determined based on the instantaneous temperature of exhaust gas at the exhaust flange. The instantaneous temperature at the midbed point is compared to a predetermined temperature threshold and the estimate rate of misfires is compared to a predetermined misfire rate threshold.