BMW K bikes (Bricks)

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robmack

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There has been a popular graph floating around that shows the negative temperature coefficient response of the temperature sensor used in the 2 valve K100 bikes.  It has been difficult to read a given resistance given a particular temperature on this graph. I thought I'd improve that graph.

Today, I recorded a set of data from a new temperature sensor that was obtained from Euro Motoelectric.  I've included the resulting graph as a PNG graphic file.  The raw sensor data is here.



The vertical axis is resistance in Ohms between one of the terminals and the body of the NTC temperature sensor, the horizontal axis is temperature in °C.


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Robert
1987 K75 @k75retro.blogspot.ca
2011 Moto Guzzi V7 Racer
http://k75retro.blogspot.ca/
    

Snod Blatter

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Just want to say thanks for this cheers 

Now, how does the injection react to this? Is it constantly changing based on the temperature from this sensor, or does it hit a certain temperature and not get any leaner? Is there a certain resistance we should aim to get under, or is lower always better? Not that mine seems to be getting richer and richer or anything


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1989 K100RS SE ABS 8v  VIN: 0149214
Others: 1.5 x Honda CBX250RS-E, '94 CB250, '95 TRX850, '16 Z250SL
http://justbikethings.blogspot.co.uk/
    

robmack

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The Bosch L-Jetronic EFI system is fully analogue in nature.  In 1980's, there wasn't digital technologies as we've come to experience and expect now a days.  So, this NTC resistor device would have driven some sort of analogue amplifier or comparator that would have changed fuelling by adjusting injector timing (total guess on my part as I don't have any documentation that describes exactly what goes on inside the ICU).  

In short, there's no low resistance factor you shoot for.  There's no AFR tables or ignition timing tables or temperature compensation tables in an L-Jetronic. You're correct in saying it is constantly changing based on the current coolant temperature being converted into a resistance reading.

The barn-door air mass sensor also contributes to over-lean or over-rich running conditions.


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Robert
1987 K75 @k75retro.blogspot.ca
2011 Moto Guzzi V7 Racer
http://k75retro.blogspot.ca/
    

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