Motronic on a BMW motorcycle

Ian Greaves igreaves at cix.compulink.co.uk
Wed Jan 3 19:07:07 GMT 1996


In-Reply-To: <199601011110.GAA11257 at coulomb.eng.ohio-state.edu>
Hi guys!
I've recently purchased a '93 BMW K1100RS motorcycle.
The thing runs O.K. when warm but the warming up phase is bloody 
'orrible! 
It always fires (starts) when cold, but then will often only run on three 
until it's cleared it's throat. I have to keep the throttle slightly open 
otherwise it dies instantly. All this is accompanied by clouds of hazy 
unburned fuel and that rich smell, coming from the exhaust. Basically, 
the machine is running well rich. (About 20mpg when running warmed up!!, 
that's at least double the consumption I'd expect.) I've replaced the air 
filter and spark plugs. Upon dismantling bits of the bike, I discover 
that the engine management uses a MAP sensor (I thought it was hot wire!) 
with vacuum tubes everywhere!! The water jacket thermistor, and the 
intake air thermistor measure about 4 K Ohms at ambient temp. (say 10 
degrees C, not unreasonable?) I can't find any obvious vacuum leaks in 
the piping, and I've opened/remade all the plug in connectors around the 
place. Any Ideas, anyone, before I admit defeat and go back to the dealer 
and his analyser!!
In fact, does anyone know anything about this particular Motronic system. 
How does one read any fault codes? I see a three terminal connecter, I 
suppose this would be a serial port. Is it clocked, or does data just 
fall out of it asynchronously? What's the baud rate, levels etc.
Also any basic set up data? (Throttle pot voltage at idle, etc.)
If anyone knows anything, let me know. a) I'd love to learn all about 
this version of Motronic, as it's not covered in any of my books. (only 
K,L and LH in the book!) and b) I might just fix my bike!!

yours Ian Greaves, in London U.K.




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