A Quick Diagnostic Method for the Electronic Control System of the Mitsubishi 4A91 Engine

A Mitsubishi 4A91 engine used in an Xpander 7-seated passenger car has an electronic fuel injection system measuring intake air mass flow with the speed-density method and a direct ignition system using coil-on plugs. Malfunctions in electric circuits, sensors, actuators, fuel delivery system, ignition system, intake manifold, and air charging system lead to apparent symptoms such as difficult engine starting, slow or hesitation at acceleration, stall while driving, intermittent power loss, check engine light illuminated, engine idle rough, excessive engine smoke, noticeable fuel odors, and decreased fuel economy. This paper introduces a quick diagnostic method to determine the causes of troubles. OBD-II live data are collected while the engine is running in different operating phases, including warming up, idling, low speed, high speed, hard acceleration, and quick deceleration. Features of collected live data in each operating phase are retrieved, and then causes of troubles can be induced via a diagnostic algorithm that compares retrieved features to those of the normal engine. This quick diagnostic method can support technicians to find out 26 different causes of troubles in less than 10 min.