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Re: Closed Loop Disable



At 08:17 PM 8/18/00, you wrote:
From a thread a while back, nikog@mediaone.net writes:

<< Using just a DVM is a GREAT way of doing your first chip. You'll learn a
lot
 with that method. Turn off closed loop/adaptation, then tune the maps to get
 450mv from the O2 sensor at all PT map locations. Note, you'll NEVER get the
 O2 to read 450mv; it'll either be above or below it. If changing the map
 value by one digit makes the O2 reading go from below to above 450mv (or
 vice-versa), rest assured that the tuning at that point is more than close
 enough. Heck, 5% off is close enough. This is exactly how I tuned my
 turbocharged M3. >>

How do you get the ECM to not use closed loop without a scanner? I
disconnected the O2 sensor but was told that that would put the ECM into limp
home mode, not open loop. My understanding was that if the ECM did not get
the O2 cross counts, that it would stay in open loop.

No, It will set a trouble code... Have to modify the prom to keep it out of closed loop with setting the coolant temp minimum to 255.




Also, I thought you could use a DVM and measure the O2 signal (disconnected
from the ECM) as a way to monitor tuning, but a recent post said the ECM puts
a bias voltage on the O2 wire. How can that bias voltage effect a
disconnected sensor? Is there a miscommunication here? Before each tuning
session, should I remove power from the ECM each time to reset the BLMs to
128?


The Bias voltage is only used when the sensor is cold. Once the sensor get's up to temp, it overrides the bias voltage... Bias voltage is so low of a current that the O2 sensor kills the bias when it starts making it's own voltage.


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