When OBDII goes into Open Loop mode
05-24-2001, 10:30 AM
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When OBDII goes into Open Loop mode
The system still uses all inputs except the O2 sensors. So the EGT,KNOCK, MAF, TEMP ect still come into play. Three reasons for the Open loop mode is in case of failure of O2 sensors, WOT operation, Cold starts till sensor are at temp...
05-24-2001, 10:50 AM
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So at WOT it is closed loop w/EGTs (but not O2 sensors)
I was told that at WOT if EGT gets above a certain temperature, fuel is added (on top of what is already programmed in the open-loop lookup table) to reach a desired EGT. To me this makes sense - what more important time to utilize EGT feedback than at WOT.
05-24-2001, 11:12 AM
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It's open loop at WOT..
don't worry I always confuse the terms.. None the less, EGT feed back is used at WOT. So more fuel is delivered if it gets to high, the O2 sensor is not used in an attempt to make it run a richer...
05-24-2001, 12:02 PM
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Well technically it's NOT open loop in the general sense because it uses EGT feedback.
That is what you call a close-loop system. But yeah if it doesn't use O2 sensors, then the term 'open-loop' applies in that case. It's just not purely open-loop.
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05-24-2001, 12:16 PM
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Well, it's open loop in that it doesn't cycle the mixture from rich to lean to average stoich (sp?)
You are right though, any time you use sensors to adjust your actuators you are in a closed loop system. In WOT the ECU tries to maintain the highest possible engine output while keeping the engine intact (hence EGT and knock) while at cruise it primarily uses the HEGOs to keep the burn clean.
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05-24-2001, 01:15 PM
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Good point. By the way I had originally heard that the S4 DID use the O2 sensors at WOT
so it was closed-loop by everyone's definition. I was told it was supposedly the first turbo car that was emissions legal at WOT (I heard this from a knowledgable Bosch person who also owns an S4).
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