Abstract: A straddled vehicle, including: an engine, which includes a combustion chamber; a three-way catalyst, which is configured to purify exhaust gas exhausted from the combustion chamber; an upstream oxygen sensor, which is provided upstream of the three-way catalyst in a flow direction of the exhaust gas, and is configured to detect an oxygen concentration in the exhaust gas; a downstream oxygen sensor, which is provided downstream of the three-way catalyst in the flow direction of the exhaust gas, and is configured to detect the oxygen concentration in the exhaust gas; and a controller, which includes a processor, and a non-transitory storage medium containing program instructions, execution of which by the processor causes the controller to execute a detachment determination process of determining whether the three-way catalyst is detached at least based on a signal input as a signal of the downstream oxygen sensor.

Abstract: An object is to provide a misfire detection device and a vehicle with an enhanced detection reliability. A misfire detection device includes: a rotation speed acquisition unit configured to acquire a rotation speed of a rotator rotated by a four-stroke engine; a misfire determination unit configured to determine the presence or absence of a misfire in the four-stroke engine based on the rotation speed of the rotator acquired by the rotation speed acquisition unit; and a periodic fluctuation detection unit configured to detect a periodic fluctuation contained in a rotation fluctuation of the four-stroke engine based on a rotation speed acquired by the rotation speed acquisition unit, the periodic fluctuation being repeated on a circulation cycle of at least one element of a wrapping transmission element or a plurality of transmission wheels, the periodic fluctuation having a plurality of extreme values within the circulation cycle of the one element.

Abstract: An object is to provide a misfire detection device and a vehicle with an enhanced detection reliability. A misfire detection device includes: a rotation speed acquisition unit configured to acquire a rotation speed of a rotator rotated by a four-stroke engine; a misfire determination unit configured to determine the presence or absence of a misfire in the four-stroke engine based on the rotation speed of the rotator acquired by the rotation speed acquisition unit; and a periodic fluctuation detection unit configured to detect a periodic fluctuation contained in a rotation fluctuation of the four-stroke engine based on a rotation speed acquired by the rotation speed acquisition unit, the periodic fluctuation being repeated on a circulation cycle of at least one element of a wrapping transmission element or a plurality of transmission wheels, the periodic fluctuation having a plurality of extreme values within the circulation cycle of the one element.