Re: <E34>OBC MPG Misreadings - revisited

Subject: Re: <E34>OBC MPG Misreadings - revisited
From: gunnar_elmgren@domain.elided
Date: Mon, 02 Sep 1996 16:19:42 EDT
Fellow digesters,
i am sorry to say that the OBC in my '90 M5 still defeats me.....
Fred Meloan suggested, that the correction factor for calibrating the
MPG (or L/100km) calculation might be inverse and/or non-linear.
I tried this out today, and found that my OBC follows the formula from
the FAQ: NEW CF = OLD CF * (OBC MPG/Actual MPG)
My problem is still, that the reading is off by almost exactly a factor
2 (actual MPG is twice the OBC reading), and the correction factor range
the OBC accepts is 750 to 1250. I have tried both extreme settings, and
they do give a result of plus 25/minus 25 percent from what i get with
the default value 1000.
In any case, the range is not enough to compensate for the error i have.
Current theories include:
- - Faulty or wrong OBC
- - Faulty or missing signal from the DME/Motronic unit
- - Base setting of the OBC not correct for M5
Next step is to borrow the OBC from another M5 and test, to see if
it makes any difference, and to compare the part numbers etc.

I have also found a deviation from the FAQ (which describes an E36 OBC)
in the 'lock/unlock secret functions' of the E34 OBC:
To unlock:- Press the DATE key, and add the day + month numbers
          - Press 1000 and 10 simultaneoulsy, then use 10 and 1 keys
            to enter test 19
          - Press S/R once. You will now see 0000LOCK or similar
          - Use the 10 and 1 keys to enter the sum of day + month
          - Press S/R -- secret functions are unlocked...
          - Verify by entering test 19 again. Display should show FREE
To lock:  - Press 1000 and 10 simultaneoulsy, then use 10 and 1 keys
            to enter test 19
          - Press S/R once. You will now see FREE or similar
          - Press the little square button (F/C) to the left of display
          - Verify by entering test 19 again. Display should be 0000LOCK.
The procedure to show the version number also differs from the FAQ.
On the E34 OBC, you need to press the 100 and 1 buttons simultaneously,
to display the type/version (Mine shows '5-00TYP').
Any contributions to solving this mystery are welcomed. I will keep
the digest informed about my progress.....

Gunnar Elmgren
Stockholm, Sweden
BMW Club Schweden no.1436

'71 1600-2 Vollcabrio
'75 2002 tii
'90 M5 (OBC Demon)

Gunnar Elmgren
AS/400 Software Support, IBM Sweden