All I can say is, beautiful explaination! I love how these cars engine management systems are very intricate, yet in reality, very simple. Therefore if I have adjusted the mixture to the proper duty cycle (via diagnostic pins 2&3) with a suitable DMM with duty cycle function, and/or a oscilliscope for visual affirmation could I assume that I am in closed loop? However, if I assume that this constant "fine tuning" is a result of the input from multiple sensors what if one of these sensors is not within spec. or malfunctioning? Would I then consider this to be a open loop situation because the engine management systems fine tuning would now be correcting improperly from the incorrect reading(s) of the faulty sensor(s)? How would I pinpoint the culprit if my previous assumption is true? Again, I appreciate your help Steve.