Engine Manangement
Basic Description
Computerized engine management was initially developed to receive feedback from emissions control sensors and adjust basic fuel mixture and ignition timing in order to keep the exhaust gasses as clean as possible. Modern engine management systems perform the same basic functions, but have much more processing power, receive inputs from many more sensors, and have much more precise control over how the engine runs. Since 1996, engine management systems have also used a partially standardized table of diagnostic trouble codes (DTC’s). These codes provide a basis for engine diagnosis, pointing the technician to a symptom or condition that requires further investigation. This section is laid out based around the generic trouble codes. Clicking on the links will show how the part functions and the common failures it can suffer.
Technical Description
Manufacturers refer to the engine management computer with a variety of names, such as Engine Control Unit (ECU), Engine Control Module (ECM), Pwertrain Control Module (PCM), Digital Motor Electronics (DME), etc. We will use the term Engine Computer or ECU for simplicity.The ECU is a prepogrammed computer that performs several functions. The most basic function is to deliver the correct amount of fuel to the cylinders for an efficient combustion. This is done via a basic setting, and a fine tuning. The basic setting on most vehicles takes an input from the Mass Airflow Sensor and Intake Air Temperature Sensor (to determine the amount of air entering the engine), the Coolant Temperature Sensor (to determine the overall engine temperature), and, sometimes, the Throttle Position Sensor (to determine the drivers requirement of acceleration). These input numbers are compared to a preset table showing the length of time that the fuel injectors should spray in order to have the correct fuel/air mixture. The fine tuning is performed by analyzing the exhaust gasses using the oxygen sensors, and adjusting the mixture slightly to increase or decrease the amount of free oxygen after combustion.Other functions performed by the ECU include regulation of the exhaust gas recirculation system, monitoring the catalyst efficiency, controlling the Evaporative Emissions Controls, monitoring misfires, controlling the battery charge level, testing for the correct voltage and resistance in each engine management circuit, ensuring that the coolant temperature is at the correct level, controlling the radiator fans as needed, controlling the idle speed of the engine, adjusting to compensate for steering inputs and loads from Air Conditioning or electrical devices, adjusting valve and spark timing to maximise efficiency, etc.
