Abstract: A method for maintaining clean spark plugs in a variable displacement engine in which at least one group of cylinders is disabled in response to the engine load being less than a predetermined value. A first timer determines the maximum period that the engine may be operated with the first group of cylinders being disabled. A second timer controls the period of time the previously deactivated cylinders need to be reactivated to clean the spark plugs, after being deactivated for the maximum period of time.

Abstract: An emission control system including an auxiliary catalytic converter (50) coupled upstream of a main catalytic converter (44) via a bypass valve (52). Exhaust gas flow is first routed through the auxiliary converter (50) by opening one bypass valve (52) and closing another (48) when an indication of exhaust gas temperature is above a predetermined temperature. An indicating signal is derived from transitions in output of an exhaust gas sensor (58) position downstream of the auxiliary converter (50). Degraded operation of the auxiliary converter (50) is provided when both the indicating signal indicates degraded operation and an indication of inducted airflow exceeds a preselected airflow (324). Degraded operation of one bypass valve (48) is provided when the indicating signal indicates degraded operation and the inducted airflow is below the preselected airflow (340-354).

Abstract: A system and method of controls air/fuel ratio of an engine having exhaust manifolds from first and second cylinder banks coupled to a single catalytic converter. Fuel delivered to the cylinders of the first cylinder bank and the second cylinder bank are adjusted in response to respective first and second upstream exhaust gas oxygen sensors coupled to the first and second exhaust manifolds, and a downstream exhaust gas oxygen sensor positioned downstream of the converter. An inferred signal is read from a table having the first and second sensors as their inputs. This inferred signal is an inference of an output from a hypothetical exhaust gas oxygen sensor exposed to a hypothetical blended mixture of exhaust gases from the first and second exhaust manifolds. Converter efficiency is indicated by a ratio of a count in transitions between output states of the downstream sensor to a count in transitions between output states of the inferred signal.

Abstract: A control system which controls engine air/fuel ratio and provides a measurement of efficiency in the catalytic converter coupled to the engine exhaust. Fuel delivered to the engine is adjusted by a feedback variable which is generated by integrating an output of an upstream exhaust gas oxygen sensor and trimmed by the output of a downstream exhaust gas oxygen sensor. For each cycle of the feedback variable, peak amplitude of the downstream sensor output is determined and squared. Similarly, the peak amplitude of the feedback variable for each of its cycles is squared. An indicating ratio of the square of the sum of the squares derived from the downstream sensor to the square of the sum of the squares derived from the feedback variable indicates converter efficiency.

Abstract: A control system which controls engine air/fuel ratio and provides a measurement of efficiency in the catalytic converter coupled to the engine exhaust. At the end of each of a plurality of test periods, one of three selected ratios of output signals generated from exhaust gas oxygen sensors positioned downstream and upstream of a catalytic converter are sampled and the weighted average of the selected ratio over a plurality of test periods is determined. When the weighted average exceeds a reference ratio, an indication of converter efficiency is provided. Such an indication is also provided when the selected ratio exceeds the weighted average by a preselected amount, such as three standard deviations, for a preselected number of times. The weighted average is reset to the selected ratio when the selected ratio exceeds the weighted average by a preselected amount.

Abstract: A control system and method maintains engine air/fuel operation near stoichiometry in response to exhaust gas oxygen sensors positioned both upstream and downstream of a catalytic converter. A converter efficiency test cycle is generated during air/fuel feedback control after engine operation occurs in a plurality of airflow ranges for a period determined by a count in transitions of a feedback variable derived from the upstream sensor. Upon each transition in the downstream sensor, the measurement of inducted airflow at which such transition occurred is accumulated. At the end of the test cycle, converter efficiency is determined by an average of such airflow accumulations.