Originally Posted By: digitalSniperX1
Ok by closed loop I'm assuming an O2 sensor provides feedback and the system measures the O2 in the exhaust and adjusts mixture accordingly to reach some stoichiometric assignment. So if the response to feedback is out of range ( in this case due to hot/low density gasoline, would the controller simply default to open loop? If this isn't a valid question, please excuse the fact I'm not an ME and not an engine controller designer, and tell me where my thinking is wrong.!
Open loop is typically the W.O.T. setting.
Closed loop is where it takes the O2 sensor and feeds it back into the algorithm to tune the air fuel ratio back to the desired number, usually lean. If the injectors flow less, the closed loop will open them up for longer to get the right answer.
The delco hackers down here have found that the supercharged 6 that Holden put in my Caprice runs out to 19:1 A/F on the highway...that's really lean, and encourages a lean misfre, and also leads to higher throttle openings for a given road load.
All part of trying to get economy by being lean, and reduced pumping losses (more throttle opening).
It takes a lot to throw things to open loop at light load, and that's usually a limp home scenario.