0% on/off ratio possibilities:

1. mixture too rich
2. bad ecu
3. cable to socket 3 of X11 has open circuit


Test conditions:

- engine idling
- oil temp ~80C
- battery voltage 11-14v


page 16 of this manual explains it in detail (you have lambda control) also check for diagnostic codes on page 93 that you check with a blinking light:


http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/103/07.3-0121.pdf