Stock NBO2 switchpoints...???
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From: Commerce Twp, MI
Stock NBO2 switchpoints...??? I got to thinking today....what's up with the stock O2 switchpoints??? Why do they move the rich/lean threshold for low airflow conditions more towards the lean side? Ever notice a difference between what the WBO2 said was stoich vs. what the STFT's say is stoich for the motor when it's consuming less than 32 grams/sec of airflow? I know a few people have...
If you look at the stock switchpoint settings, you'll see that the engineers created a relationship between airflow coming in the motor and what the sensor considers rich/lean using "Closed Loop Mode." Anything above 32 grams/second, the NBO2's switch at their midpoint (550mV). However, bellow 32grams/sec., they switch at 500mV (20~26 grams/sec.), 450mV (~14 grams/sec.) and 435mV (idle).
Why would the NBO2 rich/lean threshold be different for a motor consuming 100grams/sec vs a motor consuming 10grams/sec? My LC1 will report a 12.75 AFR (1.8mV) for cruise scenarios just the same as it would when I'm running the 1/4mi. Why should the stockers be any different?
My theory...maybe the engineers jig-rigged the NBO2's to provide some sort of "lean idle" or "lean cruise" for low airflow situations??? After all, it's not like you're making huge power sitting still, right? I think I'm going to run the experiment of changing all switchpoints to 550mV when I get the time. The more I think about it...the worst thing that could happen would be a richer idle/light cruise.
Thoughts?
If you look at the stock switchpoint settings, you'll see that the engineers created a relationship between airflow coming in the motor and what the sensor considers rich/lean using "Closed Loop Mode." Anything above 32 grams/second, the NBO2's switch at their midpoint (550mV). However, bellow 32grams/sec., they switch at 500mV (20~26 grams/sec.), 450mV (~14 grams/sec.) and 435mV (idle).
Why would the NBO2 rich/lean threshold be different for a motor consuming 100grams/sec vs a motor consuming 10grams/sec? My LC1 will report a 12.75 AFR (1.8mV) for cruise scenarios just the same as it would when I'm running the 1/4mi. Why should the stockers be any different?
My theory...maybe the engineers jig-rigged the NBO2's to provide some sort of "lean idle" or "lean cruise" for low airflow situations??? After all, it's not like you're making huge power sitting still, right? I think I'm going to run the experiment of changing all switchpoints to 550mV when I get the time. The more I think about it...the worst thing that could happen would be a richer idle/light cruise.
Thoughts?
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Here's a post on HPTuners showing how the O2 switchpoints work.
http://www.hptuners.com/forum/showthread.php?t=4929
http://www.hptuners.com/forum/showthread.php?t=4929
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From: Commerce Twp, MI
That thread basically confirms what I suspected, which brings me to my next point. People who use the NB02's to tune their VE need to change the O2 switchpoint table to 550mV across the board. Otherwise, they'll be tuning the VE to a leaner than stoich AFR for lower airflow scenarios. Not exactly where you want to be when creating a foundation for your tune if you ask me...
Good theory, but my personal experiences kind of contradict that. I've tuned a couple cars by narrowbands for the lower RPM's, only to have them verified as dead-nuts on 14.6-14.7 with a wideband when we went back for more tuning later. Granted, this is only a couple cars, but both had SVO 30lb injectors, so switching might have been theoretically off by a little.
Originally Posted by SSpdDmon
My theory...maybe the engineers jig-rigged the NBO2's to provide some sort of "lean idle" or "lean cruise" for low airflow situations???
Narrowbands create voltage based on oxygen flowing by the sensor and are also a bit sensitive to heat. Air-flow through the system does change these factors.
I believe that at low airflow, the sensors are running cooler, and simply produce a lower voltage. On the high end, I think they raised the points to offer some protection by fattening up at high airflow.
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From: Commerce Twp, MI
Originally Posted by white2001s10
The rigging that you suggest is how they calibrated the sensor output for the changing airflow and temperature, since the sensor itself is a rather cheap, generic, and non-linear output device. I'd say they got it right for the sensor being used.
Narrowbands create voltage based on oxygen flowing by the sensor and are also a bit sensitive to heat. Air-flow through the system does change these factors.
Narrowbands create voltage based on oxygen flowing by the sensor and are also a bit sensitive to heat. Air-flow through the system does change these factors.
Originally Posted by GuitsBoy
I believe that at low airflow, the sensors are running cooler, and simply produce a lower voltage. On the high end, I think they raised the points to offer some protection by fattening up at high airflow.
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