What is meant by closed loop and open loop?
[back] OPEN/CLOSED LOOP — indicates the operational mode in which the fuel is being delivered and can also indicate the mode that idle speed is operating in. OPEN LOOP — Is a predetermined (calibrated) amount of fuel delivered based upon current engine operating conditions. These can be but are not limited to coolant temp., throttle position, engine air flow (map or maf), and time since start. An engine starts up in open loop, after a predetermined time and temperature it will go into closed loop. WOT operation is also open loop to allow for richer A/F mixture required for maximum power. CLOSED LOOP — Running condition where the exhaust oxygen content is measured with an O2 sensor. A rich/lean signal is relayed to the ECM where it causes a rich or lean command to maintain a 14.7:1 A/F ratio. This rich/lean “dithering” is what creates the full efficiency of a catalytic converter. Gasoline engines are most efficient for emissions constituents at this 14.
