Method and system for diagnosing a secondary air supply for an internal combustion engine

A method for diagnosing operational performance of a secondary air system used in an internal combustion engine, such engine producing exhaust gases, such exhaust gases passing through a catalytic converter, such engine including an exhaust gas oxygen sensor, such secondary air system introducing air into the exhaust gas after engine start-up, such oxygen sensor producing a feedback control signal during a feedback mode for adjusting engine operating air-fuel ratio, such feedback mode being initiated at a first time, such method comprising:

• operating a fuel control system for the engine during a first period of time in an open loop mode wherein a fuel control system of such engine operates independently of a signal produced by the oxygen sensor;
• operating the fuel control system for the engine during a second period of time after the end of the first period of time in a closed loop condition wherein the signal from the oxygen sensor is used to provide a feedback control signal for the fuel control system and in response to the oxygen sensor signal such fuel control system adjusts fuel injection into the engine to drive the exhaust gas towards stoichiometry;
• measuring the time period between the time the fuel control system switches to the feedback mode until the oxygen sensor indicates that a predetermined exhaust gas air-fuel ratio is produced;
• and
• comparing the measured time difference with a predetermined threshold time.

A system for diagnosing operational performance of a secondary air system used in an internal combustion engine, such engine producing exhaust gases, such exhaust gases passing through a catalytic converter, such engine including an exhaust gas oxygen sensor, such secondary air system introducing air into the exhaust gas after engine start-up, such oxygen sensor producing a feedback control signal during a feedback mode for adjusting engine operating air-fuel ratio, such feedback mode being initiated at a first time, such system comprising:

• an engine control system programmed to:
• determine 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;
• and
• diagnose the operational performance of the secondary air system as a function of the determined second time.

A system for diagnosing operational performance of a secondary air system used in an internal combustion engine, such engine producing exhaust gases, such exhaust gases passing through a catalytic converter, such engine including an exhaust gas oxygen sensor, such secondary air system introducing air into the exhaust gas after engine start-up, such oxygen sensor producing a feedback control signal during a feedback mode for adjusting engine operating air-fuel ratio, such feedback mode being initiated at a first time, such system comprising:

• a fuel control system for controlling fuel injection into the engine:
• and
• an electronic engine controller programmed to:
• operate the fuel control system for the engine during a first period of time in an open loop mode wherein the fuel control system of such engine operates independently of a signal produced by the oxygen sensor;
• operate the fuel control system for the engine during a second period of time after the end of the first period of time in a closed loop condition wherein the signal from the oxygen is used to provide a feedback control signal for the fuel control system and in response to the oxygen sensor signal such fuel control system adjusts fuel injection into the engine to drive the exhaust gas towards stoichiometry;
• measure the time period between the time the fuel control system switches to the feedback mode until the oxygen sensor indicates that a predetermined exhaust gas air-fuel ratio is produced;
• and
• compare the measured time difference with a predetermined threshold time.