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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: franck on January 03, 2016, 01:38:36 PM
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I have been working my way through Jeff Dunkles notes on fan system dianostic for 2 valve k bikes and I would like some help.
I am working on a 1986 k75c which has sat in a corner of a garage for about 18 years. I have been working my way through the machine which now runs but.... there is always a but.... when I started work I found a rat had eaten the wires to the temperature sensor. I have repaired these but I have some misgivings about the connections.
Q. Does the sensor work on the resistance difference between ground and the sensor connection? or is the difference in resistance between the two connectors ? Looking at the circuit diagram the second looks unlikely!
I removed the sensor and bench tested it - all ok. Body of the sensor to each pin 3000 ohms to about 300 ohms
I checked continuity between the sensor connector and pin 9 on the switch unit-ok and continuity to pin 10 on the injection control unit - ok I then went through the checks for the fan and the warning light - all ok.
However I get infinite resistance between pins E and 9 on the switch. (Jeff's notes talk of 3000 ohm at room temperature) I have the cooling system stripped down at the moment but I did try connecting the battery and the injector control - again infinite resistance.
Am I missing something?
Finally - thanks to you all on moto brick for such good info. I have never worked on a BMW before and to show my age never on a bike with this level of electronics (I spent the first hour looking for the carbs!). Without your site I would have given up ages ago.
Best wishes
Franck
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Are you trying to find understand why your fan doesn't work?
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I've tested the fan and it works ok - my worry is about the connections on the temperature sensing switch and the temperature sensor - Jeff Dunkle notes talk of a resistance between pins E and 9 on the switch of about 3000 ohm at room temp - I get an open circuit. I would like to check on this before putting the cooling system back in place.
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Bert Vogel's diagrams suggest to me that you should check a different pin for those values, if I'm understanding all this correctly.
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Q. Does the sensor work on the resistance difference between ground and the sensor connection? or is the difference in resistance between the two connectors ? Looking at the circuit diagram the second looks unlikely!
Yes, the temp relay sensor measures resistance relative to ground. The second NTC resistor is used for the ECU; they both just happen to share a common ground connection.
However I get infinite resistance between pins E and 9 on the switch. (Jeff's notes talk of 3000 ohm at room temperature) I have the cooling system stripped down at the moment but I did try connecting the battery and the injector control - again infinite resistance.
Am I missing something?
Jeff's notes on IBMWR seem to be flawed; should read ~3000 Ohms between Pin "E" and ground. Pin 9 is relay power from Fuse #6 (FYI: the temperature relay is actually a complex electronic circuit and needs a source of power). There is no electrical relationship between those two pins and you should read infinity Ohms.
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Thanks for your help - I must admit I was a bit confused by the resistance check. I will now reassemble and get ready for getting back on the road.
Every step of resurrecting the K75 has been enjoyable and to my wife's dismay got me back into motorcycle maintenance!
once again thanks
Frank