Motronic timing and mixture switch

[Cjarvis]

It wouldn't be SESF without a tech session. This year was a rough running M88. If we had the information below, we could have done field surgery on Lee's ECU. But he may have been the one requiring anesthesia for that one.

Anyway, Dont remember where I got this info or who the author is. Lee's car being from CO could be set to position 3, and in need of resetting to position 0.

Adjusting the switch inside the Bosch Motronic DME unit.

NOTE! This is my translation from finnish to english. It might be written in finglish (finnish english) and native english users might understood it
perhaps in different way than I meaned to.

Bend out the seal plug of the control unit by using screwdriver or other sharp tool. Turn carefully the switch counter-clockwise towards the left
side limiter by using proper tool. Count and write down the number of "snaps". Turn carefully the switch to the position you prefer according to
table. Install a new seal.
http://forums.bimmerforums.com/forum/picture.php?albumid=2148&pictureid=13416

[Layne]

Very interesting, I can see that fooling with it without this information would have been a mistake since the positions aren't exactly in order. :D I always thought the screw was a potentiometer instead of a switch. I have no idea where to get the triangle shaped driver to adjust it, I've never even seen one.

Lee should have the 055 ECU.

[eric1ono]

This is interesting information. What is/are the determining factor(s) as to which switch position you would want to have?

Eric

[ShapeShifter]

IIRC, altitude.

[Cjarvis]

I'm not an expert. But my guesses are (on the 055 ECU) that 3 is high altitude (less fuel to go with thinner air), and 4-7 are are for situations where lower octane or lower quality fuels are all that is available. Dont know what BMW might have intented on 1 and 2. Might be useful for bored and strokes motors but doubt that was thier intent?

[88m53453]

was to compensate for poor fuel originally was what i was always told....back in 83 when the 3.2/3.3 engines were giving them fits on driveability, sw pos 1 was a fix to richen the mixture a touch. Notice there were no timing advance positions,,,,drat

[Layne]

Poor gas compensation makes a lot more sense. Especially for the various worldwide markets. The AFM automatically compensates for altitude, although it's possible it would work better with some adjustment.