METHOD AND SYSTEM FOR DIAGNOSING MULTIPLE CYLINDER ENGINE

摘要

PROBLEM TO BE SOLVED: To improve diagnosis accuracy of imbalance of air-fuel ratios between cylinders in a multi-cylinder engine 1.SOLUTION: An engine system has the multi-cylinder engine 1 and a sensor 47 which is located on an exhaust gas passage 95 of the multi-cylinder engine 1. In the engine system, an exemplary diagnosing method diagnoses the multi-cylinder engine 1 by using a sensing value which the sensor 47 outputs and is associated with the air-fuel ratio in each cylinder. The diagnosing method includes: a step where a processor 211 calculates the square of a difference of the two sensing values which are output from the sensor 47 at each separately timing; a step where the processor 211 integrates the resultant square value a predetermined times; and a step where the processor 211 diagnoses the multi-cylinder engine 1 on the basis of a diagnostic parameter which is the resultant integrated value.