Hi!

I have a problem with my K100 that started with a bad Hall sensor. When searching for that fault I also found bad fuelpump (changed) and had to change rubber and filter in tank. I also changed one coil, some rubber parts to avoid vacum leaks, and o rings on injectors. Checked connector under tank, should be ok.

Still i have problem with the bike. It works great the first 30 seconds but after that it doesnt run well. All 4 Spark plugs are black. When cold down it works fine again for another 30 seconds.

What can I do next? The weather here in Finland is great and of course bike is broken...

https://www.k100-forum.com/t14705-tuning-my-k100

http://www.bmw-k100rt-page.eu/manual/Ignition/contentIgnition.htm

http://www.bmw-k100rt-page.eu/maintenance/contentMajorService.htm

1. Are spark plugs Bosch X5DC or NGK D7EA with spark plug 5KΩ wires

2. Check/clean with DE-oxit/reseat the ICU and ECU connector plugs

3. Check/adjust throttle position switch

http://www.bmw-k100rt-page.eu/manual/FuelOil/17_FuelLub.htm

4. Syncro throttle bodies   https://www.youtube.com/watch?v=gWCR3D8YMNs

http://www.bmw-k100rt-page.eu/manual/FuelOil/17_FuelLub.htm

5. Clean Injectors  Soak injectors in Denatured Alcohol many videos on cleaning injectors

6. Valve adjustment   https://www.youtube.com/watch?v=bFkPnLVkxWQ

7. check/clean the Temperature Sensor connector plug located behind the radiator

8. Remove Vacuum Switch - one less thing to worry about

http://www.bmw-k100rt-page.eu/manual/Ignition/8_IgnitionSystem.htm

https://www.k100-forum.com/t15097-what-is-this#176829

Fairing removal

http://www.bmw-k100rt-page.eu/manual/FrameForks/15_FrameForks.htm


Dark and wet spark plugs would indicate a rich condition. If this is so, then suspect the engine temperature sensor. If the sensor is faulty and the ECU thinks a hot engine is still cold the moto will run rich
Good Luck with your moto

30 seconds is not long. Too short for any coolant temperature sensor.

Your description could have a smell of excessive pressure in fuel line.

Are the spark plugs wet after your engine has self stopped?

Have you a way to measure the fuel pressure in the injection line? If so, which value? Should be around 2.5 bar.

If you do not have the equipment to measure the pressure, is there a rather important fuel flow when you disconnedt the pipe of fuel return to the tank and press the start button to trigger the pump (which will stop automatically after a couple of seconds if the engine does not start)? Caution, the engine might start and last for more than 30 seconds. Have a container handy

If you have such a flow, what happens when you blow air in the return pipe, does it generate bubbles in the tank? The "anti return" ball at the tank return point could be blocked, ruining the pressure adjuster effect. 

If there is no flow in the pipe back to the tank, your fuel pressure adjuster is most probably faulty.

It could be the water temp sensor but 30 sec is very fast.
It sound more like an electronic component over heating It.
Have you check my EFI troubleshooting page?
But......
You have to find what cuts off: Ignition or Fuel injection? Use a strobe light to alternatively test the 4 cylinders for ignition and an LED installed on one fuel injector plug will give you a good indication.
As other suggested, it could be a problem with the fuel pressure.... As you have replaced parts inside the tank, are you sure that the return line is fully functioning? A blocked return line will certainly increase the pressure and the flow in the cylinders.
Also, you replaced one coil.... there could be a problem there too.

Hi!

Thanks for advices!

Update: tested another air flow meter, injection control unit, spark plug set. Changed fpr. Still have the same problem except for now the bike only runs fine a few seconds. Also checked that fuel return line is ok.

Here you can see a short video. Bike starts fine bit after a few seconds it starts to run badly.
https://drive.google.com/file/d/1--Z7rVtvT-slBVSyWB3njQZqgOwF-Ywi/view?usp=drivesdk

Have measured fuel pressure and that seems ok.

Update again: reconised that 2 (or is it third) cylinder only works the first seconds and then stops working. Tried another coil and also switched places for ignition cables. Still same cylinder stops work. Spark plug is wet so it gets fuel. Ehat to check next?

If there is no spark in cylinders 2 and 3, that might point to the coil. Is that the coil you replaced?

Your subjects starts by the replacement of a Hall sensor.
Are you sure of the one you fitted?

Are your valves clearances ok?

Did you touch your exhaust pipes after the engine stops, in order to find out which one(s) is eventually colder than the others?

And the problem was....a dirty injector. Thanks for the help! Found it when switching injectors between cylinders! Really strang that it worked some seconds when starting.