Re: Urq sorting out

[Huw Powell <audi@mediaone.net>]

> Currently the car idles just OK (very stable but not quite right to the ear),
> and gives the spec readings for DC and voltage output of the O2 sensor when
> tinkered with long enough. These readings are so sensitive to the 3 mm
> mixture screw that a barely perceptible turn of that screw sends it rich or
> lean (i.e., ever slight turn CW sends O2 voltage to around 100 and the DC to
> 4.8; while a nudge CCW sends both to 600-700 and 62.7 respectively). This
> tells me the sensors and ECU are trying to do their job but something is
> preventing said result (say a vacuum source to the wrong port maybe?). The DC
> valve does its buzz thing at the appropriate times, so I know it's
> functioning.

Your system is not working yet...  The ecu is running open loop, I'm
sure, and ignoring the OXS signal.  Why?  You must find this out.

there isn't a "sweet spot" on the mixture screw that is the only one
that works - you should be able to turn it over at least a half turn
range and have a functioning system, good idle and general operation. 
Somewhere in that range you pick a point that corresponds to a frequency
valve duty cycle you like, I used to shoot for just under 50%, some
turbo people like it as low as 35-40% (allows more room for enrichment
on boost).  But whether the static mixture yields a warm idle duty cycle
of 40% or 60%, the engine should run and drive fine.  WOT behaviour will
vary though.  Doesn;t sound like you've gotten to that yet. 

Turning the mixture screw a little bit should alter the duty cycle (the
thing that has the duty cycle, the device, is called the frequency
valve, btw) but the OXS output voltage should keep oscillating around
about .5 volts for a wide range - until the duty cycle is pegged, won't
go higher or lower, THEN the engine will start to run rich or lean.  If
the system is working, anyway.

I'm posting this to the list to get edited/proofread... if anyone
notices any glaring errors please correct!
-- 
Huw Powell

http://www.humanspeakers.com/audi/

82 Audi Coupe; 84 4kq; 85 Coupe GT; 73 F250