Abstract: A method for diagnosing operational performance of a secondary air system used in an internal combustion engine. The engine produces exhaust gases. The exhaust gases pass through a catalytic converter. The engine includes an exhaust gas oxygen sensor. The secondary air system introduces air into the exhaust gas after engine start-up. The oxygen sensor produces a feedback control signal during a feedback mode for adjusting engine operating air-fuel ratio, such feedback mode being initiated at a first time. The method determines from the signal produced by the exhaust gas oxygen sensor a second time relative to the first time when the oxygen sensor signal indicates that a predetermined exhaust gas air fuel ratio is produced. The operational performance of the secondary air system is diagnosed as a function of the determined second time.

Abstract: A method for determining a condition of a catalyst disposed in an exhaust of an engine. The method includes sensing a common property of both the exhaust upstream and downstream of the catalyst; taking samples of such upstream and downstream sensed property over a period of time; accumulating the samples over the period of time; determining statistical characteristics of the sensed common property of the upstream and downstream common property; comparing the determined statistical characteristics of the sensed upstream property with the determined statistical characteristics of the downstream property to determine whether catalyst was in a proper operating condition during such period of time. With such method statistical characteristics are determined from samples as they are obtained and then once obtained, processed to determine the condition of the catalyst. Such method thereby reduces memory or data storage requirements and also reduces computational requirements.

Abstract: A system and method for monitoring a conditioning catalyst positioned upstream of an oxygen sensor used for feedback control of an internal combustion engine include comparing shapes of an upstream oxygen sensor signal and of the signal from the oxygen sensor used for feedback control of the engine while ignoring the signal amplitudes and mean values. Operational efficiency of the conditioning catalyst is determined based on a measure of the relative similarity or difference between the two signals.

Abstract: A method for determining deterioration of an exhaust gas sensor coupled downstream of an emission control device by monitoring the sensor's response to a change in an air-fuel ratio is presented. In particular, the sensor is monitored for a predetermined time period following a switch from lean to rich operation and a ratio of a maximum and minimum value is determined. The ratio is then compared to a threshold value to evaluate sensor performance. This method achieves improved emission control and fuel economy.

Abstract: An engine control for an automotive engine having an inlet system and an exhaust system includes an EGR valve for permitting exhaust gas to flow from the exhaust system to the inlet system, and an engine controller for operating the EGR valve by opening the valve during successive test periods separated by non-uniform intervals, while measuring engine speed response to the opening of the EGR valve so as to diagnose an improperly operating EGR valve.

Abstract: Air is purged through a fuel vapor recovery system to induct a mixture of purged air and fuel vapor from the fuel vapor recovery system into an engine air/fuel intake. An air/fuel vapor ratio of the inducted mixture is provided from a hydrocarbon sensor positioned in the engine air/fuel intake. Fuel vapor flow is then calculated and this calculation used to adjust fuel delivered to the engine to maintain a desired lean air/fuel ratio.

Abstract: Fuel vapors are purged from a fuel system into an engine air/fuel intake and the mass flow of such vapors are adaptively learned during a fuel vapor learning mode. When operating in a lean air/fuel operating mode, the lean mode is periodically disabled and the fuel vapor learning mode periodically enabled to update the measurement of inducted fuel vapors. Fuel delivery to the engine is corrected by such measurement to compensate for inducted fuel vapors and maintain engine operation at the desired air/fuel ratio.

Abstract: Fuel vapors are periodically purged from a fuel system into an engine's air/fuel intake. A measurement of the massive inductive fuel vapors is provided by a purge compensation signal is derived from an exhaust gas oxygen sensor output. Lean air/fuel operation is enabled when the purge compensation signal is below a predetermined value.

Abstract: A method and system for monitoring fuel delivery to an internal combustion engine having a first and second mode of operation and controlling the engine accordingly. An oxygen content of exhaust gas emitted from the engine is sensed and a corresponding oxygen content signal is generated. Air fuel ratio correction data is determined based on the oxygen content signal. If the engine is operating in the first mode, the air fuel ratio correction data is compared to a first set of predetermined air fuel ratio correction thresholds and a first failure signal is generated based on the comparison between the air fuel ratio correction data and the first set of predetermined air fuel ratio correction thresholds.

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.

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 control system which controls engine air/fuel ratio while providing a measurement of efficiency in the catalytic converter coupled to the engine exhaust. A test period is completed when counts in transitions of a feedback variable derived from an exhaust gas oxygen sensor positioned upstream of the converter have reached a preselected count for each of a plurality of inducted air flow ranges. Converter efficiency is determined during the test cycle by comparing an integration of the feedback variable, after band pass filtering and rectification, to an integration of a downstream exhaust gas oxygen sensor after its output is band pass filtered and rectified.

Abstract: A control system which provides air/fuel feedback control while measuring catalytic converter efficiency. An efficiency test period is provided when the count in transitions of a signal related to an upstream exhaust gas oxygen sensor reaches a maximum count for a plurality of inducted airflow ranges. During the test period, three separate ratios indicating converter efficiency are provided. These ratios include: a ratio of downstream exhaust gas oxygen sensor total amplitude to a feedback variable derived from the upstream sensor; a ratio in frequency of transitions of the downstream sensor to frequency of the feedback variable; and a ratio of areas derived from the downstream sensor and feedback variable. When all three ratios indicate degraded converter efficiency, an overall indication is provided.

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 which provides a measurement of efficiency in a catalytic converter coupled to the engine exhaust. For each inducted airflow range in which the engine is operating, test periods are generated by counting transitions in the output of an upstream exhaust gas oxygen sensor. These test periods are limited to a maximum count. Concurrently, during each test period, transitions are counted in a downstream exhaust gas oxygen sensor. Upstream and downstream transitions are accumulated and a ratio of the accumulated totals determines converter efficiency.

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.

Abstract: An electronic engine control system for use with differing fuel types, such as gasoline, methanol and mixtures of the two, controls engine operating parameters such as the fuel/air ratio and ignition timing in response to fuel-type indications generated by a fuel type sensor positioned on the fuel line. Changes in the fuel type passing the sensor result in variations in the engine control signals which are effective after a variable delay period elapses. The duration of the variable delay period is altered in response to changes in fuel pump voltage and fuel temperature to form a better estimate of the transport delay experienced by the fuel as it passed from the fuel-type sensor to the engine's fuel intake. A microcontroller delays the control signal changes by retrieving a count value from a two-dimensional lookup table indexed by values reflecting pump voltage and fuel temperature.