Re: Motronic question

[DeWitt Harrison <de@aztek-eng.com>]

On Thu, 07 Oct 1999 10:57:29 -0700, SJM wrote:

>The Motronic ECU as used on the Audi 20V Turbo engines (and likely most
>other non-Audi engines), uses the O2 Sensor signal to vary the fuel
>injector pulse width to tweak the mixture. It uses the O2 sensor voltage
>transition across the 0.450 Volt mid point to fine tune the mixture for
>best emissions when in closed loop to approximate the 14.7 to 1 A/F ratio.
>
>If you use a 2 channel Oscilloscope, with one channel you can view the O2
>sensor signal slowly oscillating up/down, (1-2 times/sec) and on the other
>channel, watch the fuel injector pulse width change slightly in response to
>the changing O2 sensor voltage signal.
>[ ... ]
>You need the VAG1551/2 factory scan tool, or equivalent CarComp/VDS Pro
>software package to read the actual stored adaptive mixture set point
>inside the ECU. The ECU uses a number from 0-255 to indicate this mixture
>set point.
>[ ... ]

Scott, thanks much for the Motronic info. Would you hazard a guess that
when the closed loop was operating near the middle of it's control range
that the value of that ECU variable you referenced would be about half of full
scale or around 127? (In case I can mind-meld with the thing.)

DeWitt Harrison
Boulder, CO
88 5kcstq
87 635CSi