I can't help you much but I can offer some suggestions that may help a little.
Firstly, you got way ahead of me becuase my german version Touring had only 3 wires on the green connector instead of the full compliment of 26 wires!. I need to find the rest of the wires from the dash and "drag" them to the OBC to function.
My 89 sedan had the factory OBC and it had the stalk. So, firstly, OBC reading does not show on the Console display becuase your stalk is not connected!. You need the stalk working and press it then the values on the OBC will show. So find a way to connect up the stalk.
Now, on the MPG reading which is still zero. I suspect a missing pin or wire there. got to find out which pin and test it with DVM.
This will also screw up the range numbers. How long have you ran the car on the OBC to date ?. Weeks or just days ?.
Use special codes to check you fuel tank level. Press 100 and 10 keys simultenously, you will get the "TEST" prompt, then use 1 key press until you get TEST 7 then press S/R. This will give you percentage of tank full. Should give you the correct figure. Mind you full tank show 75.6 or there abouts NOT 100%! In my sedan when it comes to 40% or 25% it matches the fuel guage display value almost exactly. This is the figure I needed from the darn OBC.
The temp wiring thats missing ?. I got the same problem there is no wiring in place. I suspect non-optioned models lack the termination wiring piece, unlike the US models which had the wiring all the way to the terminating connector. Hence, there is a bigger connector near the firewall that has 2 wire connector. The trick is to find this connector. It has eluded me for some time...
Also: I was told that the OBC part ending with 055 is the best to use.