This is not a complete answer, but is more data:

The Digifant I uses a 6803 microcontroller (processor). It has a whopping
128 Bytes of RAM (yes, bytes), 64 big bytes of that is retainable during
power down. So, yes, it can (does) retain settings on power down. See more
here: http://www.kenneke.com/vwfi

I'll look in the Bosch FI manual to see what it says about the reset and
service modes.

When the O2 sensor is connected to the ECU, you will see a variation as
the ECU adjust for things. It's best to measure the O2 sensor when it is
*disconnected* from the ECU. The readings should be stable at that point
(unless your AFM is messed up, among other things).

Jon

On Tue, 13 Feb 2007, Mike Frost wrote:

> Greetings all,
>
> It's time for smog testing on my 86 2.1L and I am failing for HC and CO. So
> I am looking closely at the O2 sensor which was very recently replaced.
>
> My first question is about the Digifant I ECU. I have read many differing
> statements about resetting or clearing the memory of the ECU. Does the ECU
> have any kind of static RAM (memory that does not lose its contents on
> power-down)? Does the computer reset completely when the ignition is turned
> off? Some things I have read talk about entering 'service mode' by
> disconnecting the temp II sensor and then 'blip' the throttle 3 times up to
> 3000RPM (or 4 times up to 2500). I can believe that there is a service mode,
> but I'm having trouble believing that the ECU can 'remember' the state of
> the ignition system after the engine is shut down.
>
> Second question involves the voltage from the O2 sensor. Under idle
> conditions (no change in RPM) I am seeing the voltage swing down to zero and
> then back up again to some value above 0.5V when the O2 is connected to the
> ECU. Is this normal? I'm guessing that I should see a fairly stable voltage
> unless the speed of the engine changes.
>
> Thanks in advance,
>
> Mike
> wasserleaker@gmail.com
>