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Old 01-08-2010, 03:46 PM   #7 (permalink)
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Originally Posted by cfg83 View Post
In my experience, except for cold-starts, my ECU/PCM almost never leaves closed-loop. Maybe this is another benefit of how we drive. I can datalog, so I should double-check this. Would you make the claim that even when the ECU/PCM reports it's in closed-loop, it may not actually *be* in closed-loop?
I suspect that is primarily due to the way we drive. If you mashed your throttle pedal all the way down, you would likely see the engine management go open-loop, at least for a second or two. (I know the duration of acceleration enrichment is a tunable parameter in Megasquirt, and is often in the "several seconds" range.)

I would assume that any reporting that the ECU does of open/closed loop state would be accurate, as the state is maintained inside the ECU itself. There may be other factors affecting the indication (e.g., the OBDII bus only updates information every second, and the state is only open-loop for a half-second at a time) but I'd expect it to be reasonably accurate.

--The two articles you quote from match my experience and reading on this subject pretty well. Note that these are all describing the "Narrow Band" O2 sensor; the "Wide Band" type can actually tell how far off of "stoichiometric" you are, which gives more tuning options. (Which is why that type of sensor is often used in vehicles that use lean-burn technology.)

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