The way an engine management system monitors its Air / Fuel ratio is through the Oxygen Sensor (O2) stuck in the hot exhaust flow, usually before the catalytic converter. All O2 sensors are basically the same, with some being heated or others providing multiple signal lines. An O2 sensor generates a voltage from 0-1Volt. A reading of 0 volts describes a LEAN condition, while a reading of 1 volt descrigbes a RICH condition. Autometer, Cyberdyne, Intellitronix, and many others manufacter A/F Gauges costing at least $30 or more . It is almost ...[read more]