The decisin for the ECU to attempt closed loop operation is based on coolant
temparature, time engine running, and throttle switch/engine rpm.

The signal at the O2 sensor input will effect what the ECU tries to do in
closed loop operation.

Dennis

>From: Mike Elliott <camping.elliott@GMAIL.COM>
>Reply-To: Mike Elliott <camping.elliott@GMAIL.COM>
>To: vanagon@GERRY.VANAGON.COM
>Subject: Re: Heh -- I'm such a ninnyhammer
>Date: Mon, 4 Aug 2008 07:16:00 -0700
>
>Some comments to the below:
>
>>>That said, your situation with disconnecting the O2 sensor instead of the
>>>gauge and the resulting response tells me that the gauge is a problem in
>>>itself.
>>
>>Only if disconnecting the gauge makes the symptoms disappear...
>
>That will be tested today. Yesterday's conditions were: O2 sensor
>disconnected from ECU input and meter input. Meter input and ECU input
>still connected together, meter sat steady at midscale. Unless, as was
>mentioned, the signal line had a lot of high frequency noise on it that
>the meter could not display.
>
><snip>
>
>>
>>True -- although Mike said that the meter stayed centered, suggesting
>>that the ECU was back in open-loop mode?
>
>I don't see how that indicates the ECU was in open loop, only that the
>bias voltage at the ECU input did not change -- right? Pin 5 (O2 sensor
>signal) is just a high-impedance input, yes?
>
>Possibly useful would be to disconnect the sensor signal from the ECU
>input and connect it to the meter to monitor what the engine is doing when
>the ECU can't see the sensor. David said something about biasing the
>sensor with a half-meg resistor?
>
>--
>Mike Elliott