Patent attributes
If improper fuel (light oil or kerosene) is mixed into fuel (gasoline) supplied to the engine, a knock limit of an ignition timing is retarded. Based on such a characteristic, every when knocking is detected based on a detection signal from a knock sensor, the ignition timing is stored as the knock occurring ignition timing and the ignition timing is retarded by a predetermined amount. After repeating the above processes, it is determined whether the knock occurring ignition timing is retarded more than a determination value (for example, a retarded limit value of the knock occurring ignition timing in a case that proper gasoline is served). When the knock occurring ignition timing is retarded more than the determination value, it is determined that the improper fuel is mixed in the fuel.
