Closed Loop Disable

[David Cooley]

At 08:17 PM 8/18/00, you wrote:
> From a thread a while back, nikog at 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.


===========================================================
David Cooley N5XMT Internet: N5XMT at triad.rr.com
Packet: N5XMT at KQ4LO.#INT.NC.USA.NA T.A.P.R. Member #7068
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