Mind Your Motronic

Mind Your Motronic

by | Jun 26, 1989

While reading newsletters from other BMW Clubs I have run across several “tech tip” articles which contain little useful information and suggest unnec­ essarily desperate measures which, over the long run, could cause more problems than they solve.

My current favorite tech topic is the opening of Motronic control units (commonly miscalled “fuel injection brains”) to tinker with the innards in an attempt to solve running condition problems. The problem is, there is no way to tell what the effects of these adjustments are on the  16,000 re­ sponses programmed into the MCU. Before a very expensive part is toyed with, how about checking and correct­ ing such things as spark plug type and gap, valve lash, and quality of fuel? Those are just a few of the factors that affect driveability. I have seen MCU adjustment suggested for problems where the control unit would be the last thing I’d suspect. Engine idles roughly?-adjust the MCU! Gas mile­ age down?-adjust the  MCU!  Come on folks-this  isn’t  right.

I also love the instructions for discharging any static electricity buildup before disassembling the control unit – “wipe your hands on your pants then kiss the steering wheel.” Seriously now, BMW is very concerned about inte­ grated circuit damage in electronic units caused by static electricity dis­ charge. The simpie act of sliding across a car seat can produce a voltage many times higher than the amount that will cause damage. The most common result of electrostatic discharge is a weaken­ ing of an electronic device – your adjusted Motronic unit may fail some time down the road. Wouldn’t that boost the resale value!

My favorite tech article advocates building your own Service Interval Indicator reset tool. Isn’t it just like BMW of North America to charge over $100 for a tool when you can make your own for $5? Not quite. For one thing, the pin connectors on the factory tool are precisely sized to fit the diagnostic connector. They don’t have to bejammed in at an angle as is neces­ sary with ground-down banana plugs . Also, the factory tool ensures the com­ plete and safe resetting of the SI lights by means of the electronic stuff inside the tool. SI lights are not reset when all the dash LEDs are green -only when the factory tool finishes its cycle. And what happens if the Service Interval circuitry isdamaged by a non-approved tool? Probably just the permanent illumination of the “service” light in the instrument cluster. Permanent,that is, only until you shell out several hundred dollars to replace the SI cir­cuit board.

It’s not for nothing that all newslet­ ters carry liability disclaimers . BMW may not do everthing right, but in these situations at least, Father(land) knows best.

Chuck Christensen


This article was originally published in the June 1989 edition of Zundfolge