Provided is an internal combustion engine (1) malfunction diagnosis apparatus capable of diagnosising the deterioration of an internal combustion engine (1) with a high accuracy and capable of diagnosising deterioration of a fluctuation factor detection section of the engine (1) with a high accuracy in irrespective of the engine speed.
According to one embodiment of the present invention, there is provided a malfunction diagnosis apparatus for an internal combustion engine comprises: a crank angle detection sensor (25) for detecting a crank angle of the internal combustion engine (1); a fluctuation factor measurement means (3) for measuring a state of a fluctuation factor of the internal combustion engine; an angular-based data sampling section (14A,14B) for sampling data of an output signal from the fluctuation factor measurement means (3) at a predetermined rotation angle of a crank shaft in accordance with a crank angle signal from the crank angle detection sensor (25); a malfunction judgement section (17) for judging a malfunction of the internal combustion engine (1) on the basis of data sampled by the angular-based data sampling section (14A,14B); a time-based data sampling section (21) for sampling an output signal from the fluctuation factor measurement means (3) at every lapse of a predetermined constant time; and a fluctuation factor measurement means deterioration judgement section (28) for judging deterioration of the fluctuation factor measurement means (3) on the basis of data sampled by the time-based data sampling section (21).