Abstract: A misfire monitoring method and system employ an indicated mean effective pressure (IMEP) parameter for misfire monitoring of an internal combustion engine of a vehicle. The method and system include determining displacement and torque of the engine. An indicated mean effective pressure (IMEP) parameter is then calculated for the engine. The indicated mean effective pressure (IMEP) parameter is engine torque divided by engine displacement. A misfire monitor monitors the indicated mean effective pressure (IMEP) parameter to detect misfire. The method and system include determining maximum indicated mean effective pressure (IMEP_MAX) parameter for the engine. A normalized indicated mean effective pressure (IMEP_LOAD) parameter for the engine is then calculated. The normalized indicated mean effective pressure (IMEP_LOAD) parameter is the indicated mean effective pressure (IMEP) parameter divided by the maximum indicated mean effective pressure (IMEP_MAX) parameter.

Abstract: A method and system for generating an inferred EGO sensor signal for use in monitoring operation of a catalytic convertor in an asymmetrical Y-pipe vehicle exhaust system utilizes current engine airflow and engine speed readings as address inputs for a look-up table of predetermined time delay values. The addressed time delay values are used to retrieve previously stored upstream EGO sensor signals corresponding to the time delay values. An inferred EGO sensor signal is then generated based on the retrieved EGO sensor signals, thus providing an inferred EGO sensor signal which accounts for the exhaust transport delay down the different respective exhaust pipe legs.

Abstract: A control system and method for indicating the efficiency of a catalytic converter coupled to a variable displacement engine. A preselected group of cylinders is activated in a first engine operating and all cylinders are activated during a second engine operating mode. A converter test period is provided when a count in output transitions of the upstream sensor reaches a first preselected value while operating in the first mode and count in transitions of the upstream sensor reaches a second preselected value while operating in the second mode. Converter efficiency is generated by computing a ratio of upstream sensor counts to downstream sensor counts during the test period.