OVERVIEW ON EFI ELECTRONIC FUEL MANAGEMENT SYSTEMS

There are many different variations of electronic fuel injection systems manufactured by a number of different specialist companies like Bosch, Bendix, Rochester, Weber etc. as well as hybrid systems developed by engine manufacturers themselves such as Toyota, Mazda, Renault --- and they are being modified and improved daily so we can only speak in general terms. The information required by the on-board fuel management system is provided by a number of sensors located throughout the engine and this information tunes the engine for cold starts, altitude, high and low speed, fuel surge, rapid acceleration/deceleration etc. The sensors in a typical modern fuel injection system include. Intake Air Temperature Sensor Intake Air Flow Sensor Exhaust Temperature Sensor Manifold Pressure Sensor Fuel Pressure Sensor Barometric Pressure Sensor Throttle Plate Potentiometer Sensor Engine Speed Sensor Intake Air Flow Sensor Oxygen Sensor An oxygen sensor mounted in the exhaust of the engine measures the oxygen left after combustion to determine if the air/fuel ratio going into the combustion chamber is too rich or too lean. The signal is sent to the engine management computer and the mix is adjusted accordingly. An oxygen sensor can prevent fuel saving technologies that create a leaner mix from working. Creating a leaner mix may save fuel but sacrifice power or reduce engine performance in various ways or affect the catalytic converter so the oxygen sensor is an important part of the fuel management system. If the sensor detects a lean mix it will (in most injector systems) increase the injector pulse time to allow more fuel into the engine, thus keeping the air/fuel ratio at the pre-set value. On most vehicles this ratio is set at 14.7:1 and is the constant target ratio for optimum fuel use and exhaust emissions control. The oxygen sensor measures the oxygen left in the expelled gasses to determine how lean the mix is. It does not measure how rich the mix is so, in other words, it is constantly reducing the amount of fuel injected into the cylinder until it detects that it is too lean, then increases it slightly.