Hi all, Motor k100rs from end 1984. 

While driving my motor dropped dead. Fuel - good !, ignition problem ... - cylinder 2-3 no spark on the plugs. Coil lead switched tells me that it is the lead and not the coil itself.
Did measure all the cables in the ignition system for a broken wire or a short. No problems to find. 
Hall sensor and ECU not jet replaced as symptoms are a little more complex.  I thought that the engine should stay running when only two cylinders work - correct ?  Also, the starter motor does crank but not full power, gives a few cranks and I need to push the starter button again. Battery is good as it works properly on my other k100 motor. Also checked the brushes on starter motor - still as new, almost 12 mm long on the edges.
To exclude everything before I swap Hall sensor and ECU what wiring and/or relay I should measure ?
What could be the problem ? Or is it simple that the ECU causes the starter to crank difficult.
Thanks for your suggestions.

If starter is weak and battery is fully charged possibly brushes or other problem in it. Brush kit OEM is cheap.

Hi Oote,

Which leads were swapped, and what happened after that?

It's probably too early to say, but a simple hall sensor test is shown with photos on the thread "Starter issues - K100RS"

The injection gets i signal to fire from the hall sensor for cylinders 2-3 so that is why it wont fire even on 2 cylinders. Start by checking the hall sensors there is a how to on this subject

RicK G wrote:The injection gets i signal to fire from the hall sensor for cylinders 2-3 so that is why it wont fire even on 2 cylinders. Start by checking the hall sensors there is a how to on this subject

Thanks Rick and also the others for the trouble shooting suggestions. Helpful ! I replaced today the ICU. First just plugged it in and got again a spark on c2-3. Put it all together and again no spark... So I again took of the tank and rechecked all the wiring for a loose contact or break to the ICU. No problem in the wiring to find. Starter-motor with this other ICU does turn over normal.
I was wondering is there a relay that could cause the ICU to malfunction or even to break down after one of two short engagements on the C 2-3 ICU internals?    Thanks in advance for your input.

92KK 84WW Olaf wrote:If starter is weak and battery is fully charged possibly brushes or other problem in it. Brush kit OEM is cheap.

Richard Metz wrote that the ground of the starter is going through the ICU.

"You’d think the ground side of the relay would be wired directly to a chassis ground, as it is on many machines, but this is not the case on the K100. In fact the ground is provided thru the ignition brain and on thru the HES!!!! That’s why an intermittent HES problem causes on-off-on-off starter operation with the starter button held down."  https://ibmwr.org/index.php/1998/04/01/starter-electrical-problems/

By switching the ICU the weak starter symptoms went away. Now still having the c 2-3 spark problem to solve....

oote wrote:To exclude everything before I swap Hall sensor . . .

Test the Hall sensors first. Have you found the test in the Portal's Tech Page section in the category Testing the Hall Sensors?

I have 3 Hall’s and did do three test: Ohm / Volt / Amp


test 1- Ohm

  —  reading works only when negative of the ohm meter is on pin 4  and + on pin 3
( Pin coding is as ‘Bert 2009’  -  https://servimg.com/view/20230085/9 )

Sensor 1: unblocked and blocked*

4-3   zero Ohm /  no resistance

4-5   2.5K Ohm   

4-2   2.5K Ohm  



Sensor 2: unblocked and blocked

4-3   100% resistance

4-5    2.5 Kohm

4-2   100% resistance



sensor 3: unblocked and blocked

4-3   2.5K Ohm

4-5   2.5K Ohm

4-2   2.5K Ohm



* No difference between unblocked and blocked sensors makes sense as the ohm meter does not activate the sensors, it just measures the internal resistance of the sensor.




test 2 - Volt

sensor 1 unblocked  - 12 volt  (with is correct with the LED test light ‘on’ as it means there is a voltage)

sensor 2  - zero / no voltage

sensor 3 unblocked  - 12 volt



I conclude sensor 2 is broken.



test 3 - mAmp  (This test compared to the ohm readings becomes interesting for me.)

sensor 1 , my meter max out at 150mA , de arrow goes all the way in the corner.

sensor 2 / 0 mAmp

sensor 3  about 20 mAmp




I made a short cranking with the replacement ICU to test or it all worked, I got a spark so concluded hall sensor is good but when starting up the motor for real and it would not start having again no spark on cylinder 2-3 (The coil is good)



Is it possible that sensor 1 has broken the ICU because it sends a to high mAmp through the ICU circuit ?
( Why only the circuit of c 2-3 ?)

Anybody has had that problem to ? 

Is my diagnostic reasoning correct ?

I will replace this time both Hall sensor and again the ICU…. 


oote wrote:I will replace this time both Hall sensor and again the ICU…. 


If your intention is to replace the Hall sensor i]first[/i] then try starting the engine, that is a useful strategy.

If your intention is to replace both before trying to start the engine, that won't indicate which was faulty until they are tested in the engine separately.

I did not know what was faulty and as the Hall sensor worked / got a spark by test cranking ! I assumed the Hall sensor is okay.
The LED light test does not take the amp overload between ICU and the hall sensor in consideration. If you look at my test my sensor looks to be okay. Also, and very important, I can not find fault tests on Amp 'communication' between the hall sensors and the ICU. I am eager to know and I want to make sure before I go replacing further parts that the Amp overload is what causes the ICU to break down.

Can you please do the ohm / Amp test on a hall sensor, pins 4-3, and post your results ?
Your not helping me only, there must be more people out there with the same diagnostic problem.
Thanks in advance.

oote wrote: I assumed the Hall sensor is okay.
Thanks in advance.

You shouldn't need to assume anything; knowing is better. You've made your description of this test more complicated than I can comprehend on a Saturday. How about trying this test description from the troubleshooting guide?

Any good sensor should light the LED until something metallic, like a feeler gauge, is introduced in to the sensors gap, the LED will then go out.
 
Any sensor that doesn't light the LED or doesn't go out when the sensor gap is obstructed is defective.

Motor is fixed and drives again !  3 Hall's and 3 ICU later... 

My Hall (#1)was good according the LED test but did not work under normal working condition as posted before. Although my old Hall was not broken doing the LED test and sparked by short test (looking at the sparkplug and a short cranking), under load it stopped the ICU from functioning. That has thrown me off as my diagnostic conclusion told me I burned two ICU's. When I finally placed the Hall that measured 2.5kOhm on all pins, all three the ICU worked normal.
Why the ICU stop functioning normal on my old Hall I do not know. My conclusion from doing the various tests is that there was to many mAmp between pin 4-3.
I searched or there is an Amp overload protection within the ICU but did not find information on it.
Hope this of help to the next person with the same problem.
Happy riding !