Disclosed are a misfire diagnosis method and device for determining a misfire occurring in a single-cylinder four-stroke engine using a tooth time signal (a time required for an engine crankshaft to rotate at a certain angle). According to one embodiment of the present invention, the misfire diagnosis method for a single-cylinder four-stroke engine comprises: a signal collection step of collecting tooth time signals output by a crankshaft position sensor during one engine cycle; a speed trend line generation step of extracting an engine speed (TDC1) at the beginning of an intake stroke and an engine speed (TDC3) at the end of an exhaust stroke from the collected tooth time signals, and generating a speed trend line (L1) using the extracted two engine speeds; a speed increase/decrease trend line generation step of extracting and engine speed (BDC1) at the beginning of a compression stroke and an engine speed (BDC2) at the end of an explosion stroke from the collected tooth time signals, and generating a speed increase/decrease trend line (L2) using the extracted two engine speeds; a linear trend removal step of removing a linear trend using the speed trend line (L1) so that the engine speed (TDC1) at the beginning of the intake stroke and the engine speed (TDC3) at the end of the exhaust stroke can become the same; and a misfire diagnosis step of determining whether there is a misfire by analyzing an inclination of the speed increase/decrease trend line (L2) to the speed trend line (L1) after the removal of the linear trend.;COPYRIGHT KIPO 2020
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