Diagnostic apparatus for an engine

A diagnostic apparatus for an engine, comprising:

• an exhaust-gas purification catalyst disposed in an exhaust-gas passage, a coolant temperature sensor which detects coolant temperature of the engine, a fuel injector which injects fuel so as to form an air-fuel mixture in a combustion chamber of the engine, a rotational speed sensor which detects rotational speed of the engine, a spark plug which communicates with the combustion chamber, and a controller which is electrically connected to the coolant temperature sensor and the rotational speed sensor to control the fuel injector and the spark plug,
• wherein the controller is programmed so as to
• calculate a target engine rotational speed and a target ignition timing based upon a predetermined characteristic in accordance with the detection of the coolant temperature sensor when the exhaust-gas purification catalyst is determined to be inactive based upon the detection of the coolant temperature sensor during engine start;
• transmit a signal for an operation of the fuel injector and the spark plug to achieve the target engine rotational speed and the target ignition timing;
• calculate a cumulative amount of fuel injection from engine start;
• and
• judge that the operation is faulty if the cumulative amount of fuel injection calculated until a constant time period elapses from engine start is equal to or smaller than a threshold value, the threshold value being determined based upon the target engine rotational speed and the target ignition timing.

A diagnostic apparatus for an engine, comprising:

• an exhaust-gas purification catalyst disposed in an exhaust-gas passage, a coolant temperature sensor which detects coolant temperature of the engine, a fuel injector which injects fuel so as to form an air-fuel mixture in a combustion chamber of the engine, a rotational speed sensor which detects rotational speed of the engine, a spark plug which communicates with the combustion chamber, and a controller which is electrically connected to the coolant temperature sensor and the rotational speed sensor to control the fuel injector and the spark plug,
• wherein the controller is programmed so as to
• calculate a target engine rotational speed and a target ignition timing based upon a predetermined characteristic in accordance with the detection of the coolant temperature sensor when the exhaust-gas purification catalyst is determined to be inactivated based upon the detection of the coolant temperature sensor during engine start;
• transmit a signal for an operation of the fuel injector and the spark plug to achieve the target engine rotational speed and the target ignition timing;
• calculate a cumulative amount of fuel injection from engine start;
• and
• judge that the operation is faulty if the cumulative amount of fuel injection calculated until a time period elapses from engine start is equal to or smaller than a constant threshold value, the time period being shorter for a lower coolant temperature detected by the coolant temperature sensor.