K75 stalls at speed - ignition cuts out randomly

Hello folks,

I would really appreciate any insights into the problem I'm having. I've tried searching the internet and the old forum for an answer, but haven't found anyone else with the same problem as me.

Here's the history: last December, I put the bike away after the engine died suddenly while I was driving up a hill. I was a little confused at the time, so all the details are not clear, but I do remember distinctly that the headlight was off. The strange thing was that when I hit the engine kill switch and disabled the engine, the headlight would come back on. This made me think perhaps there was a short circuit in the engine or something, but I'm including this detail just for information, because the problem has changed/improved. Also, at the time I had one spark plug that was gapped too wide because a friend borrowed my bike. I was able to restart the bike only after turning the ignition off and on, and maybe waiting for a little while, I believe. I think this happened a few times, but then again, the engine might have also been dying because of the over-gapped plug. Before I fixed the plugs, the bike was stalling much more frequently.

Since that incident, the bike sat for three months over the winter, and I have changed the plugs, the gas and reseated the jack to the computer under the seat. Now the problem seems to have mostly gone away, but randomly (averaging maybe 5 or 10 km between incidents) the engine has cut out. This has happened just two or three times including once today while on the highway at about 90kph. (I thought the problem went away after I changed the plugs and gas). I don't think I was shifting or decelerating at the time the engine cut out. I think I was accelerating lightly. My instinct was to pull the clutch in and coast, and I hit the starter which did nothing (no sound from the starter that I could hear). I believe that the instrument panel was still lit up and it was definitely telling me what gear I was in (3rd). Despite the truck behind me, I tried dumping the clutch to bump start the engine, but it did not fire up. I tried this twice as I decelerated to about 40kph and pulled over. I believe that the headlight stayed on, and toggling the kill switch did not re-introduce the starter. After I turned the key off and on, it didn't fire up the first time (I can't remember if the starter cranked at all). I turned the key off and waited a few seconds, and turned the key back on, and this time the bike started up fine and drove me 5km to my destination without incident. After my meeting, I fired up the bike and it was fine all the way home.

This seems like a computer or sensor problem because of the loss of spark or injection, but the loss of the starter really seems to indicate the computer to me. Is there anything else besides the computer that could interfere with both the spark/injection and the starter?

I would really appreciate any feedback on this. My bike is my only personal transportation. If I were gainfully employed, I'd take it straight to the shop, but that's not really an option right now. Thanks for taking the time to read this.

Cheers,
Tony

Zitat von "wongstein"

Hello folks,

Here's the history: last December, I put the bike away after the engine died suddenly while I was driving up a hill. I was a little confused at the time, so all the details are not clear, but I do remember distinctly that the headlight was off. The strange thing was that when I hit the engine kill switch and disabled the engine, the headlight would come back on. This made me think perhaps there was a short circuit in the engine or something, but I'm including this detail just for information, because the problem has changed/improved.

Oh, Oh, this kills my quick fix theory that it might be a bad connection at the ignition switch...but clean it anyway.
Sounds like ReneZ is right about the starter motor. However, I would first of all clean ALL joints, including those under the tank and next to the battery. Undo the earth cable from the battery where ir grounds on the gearbox and clean that connection too.

Also, at the time I had one spark plug that was gapped too wide because a friend borrowed my bike. I was able to restart the bike only after turning the ignition off and on, and maybe waiting for a little while, I believe. I think this happened a few times, but then again, the engine might have also been dying because of the over-gapped plug. Before I fixed the plugs, the bike was stalling much more frequently.

An over-gapped plug could cause the engine to die at idle but not at speed.

Since that incident, the bike sat for three months over the winter, and I have changed the plugs, the gas and reseated the jack to the computer under the seat. Now the problem seems to have mostly gone away, but randomly (averaging maybe 5 or 10 km between incidents) the engine has cut out. This has happened just two or three times including once today while on the highway at about 90kph. (I thought the problem went away after I changed the plugs and gas). I don't think I was shifting or decelerating at the time the engine cut out. I think I was accelerating lightly. My instinct was to pull the clutch in and coast, and I hit the starter which did nothing (no sound from the starter that I could hear). I believe that the instrument panel was still lit up and it was definitely telling me what gear I was in (3rd). Despite the truck behind me, I tried dumping the clutch to bump start the engine, but it did not fire up. I tried this twice as I decelerated to about 40kph and pulled over. I believe that the headlight stayed on, and toggling the kill switch did not re-introduce the starter. After I turned the key off and on, it didn't fire up the first time (I can't remember if the starter cranked at all). I turned the key off and waited a few seconds, and turned the key back on, and this time the bike started up fine and drove me 5km to my destination without incident. After my meeting, I fired up the bike and it was fine all the way home.

Happy hunting. Cheers, Frank

This seems like a computer or sensor problem because of the loss of spark or injection, but the loss of the starter really seems to indicate the computer to me. Is there anything else besides the computer that could interfere with both the spark/injection and the starter?

I would really appreciate any feedback on this. My bike is my only personal transportation. If I were gainfully employed, I'd take it straight to the shop, but that's not really an option right now. Thanks for taking the time to read this.

Cheers,
Tony

Alles anzeigen

Thanks guys!

Rene, I read somewhere that BMW does some funky routing of electrical paths through the starter, so what your saying makes sense. So that'll definitely be part of the electrical cleanup which is my next step.

Zitat von "ReneZ"

Aside the normal advise to clean all your connectors I think you might want to look at your starter motor. These are known to give strange issues when getting dirty inside.

People say that the computers are dead-reliable, but I have a feeling that something like this is either corrupting the signals to the computer, or causing a fault in the wiring. I have to go over the schematic some more, but a big electrical cleanup as per you and Frank is definitely next.

Zitat von "OoB"

Oh, Oh, this kills my quick fix theory that it might be a bad connection at the ignition switch...but clean it anyway.

Thanks Frank, I will be sure to include this among the other connectors you mentioned even though the headlight symptom went away after I reseated the computer plug. The first time this all happened, it was foggy out. Now it's pretty dry in Toronto, so it could still be a contributing factor or a secondary problem.

Zitat von "OoB"

Sounds like ReneZ is right about the starter motor. However, I would first of all clean ALL joints, including those under the tank and next to the battery. Undo the earth cable from the battery where ir grounds on the gearbox and clean that connection too.

An over-gapped plug could cause the engine to die at idle but not at speed.

According to the Clymer manual, the symptom of the engine losing power under load can be caused by an over gapped plug. I could take a guess about the the arc length causing an over-voltage spark or something, but it's a pretty wild guess However, when I first brought the bike out this month, it would stall as soon as I tried to go up a garage ramp, or accelerate with any gusto. Changing the plugs and gas seemed to fix that, and now there's just this sparsely intermittent problem. But you may very well be correct - It might have been water condensation in the tank or bad gas, and not the plugs, but I thought I'd just quote the manual for the sake of information and conversation. I don't mean to be argumentative, I really appreciate your input.

Anyway, this problem is hard to repeat or rule as solved since it seems to takes about 10k of riding before it happens, so I probably won't be able to isolate the cause as being the starter or the ignition or kill switch. I'll just clean it all and see if I have the problem again in the next 100k or riding.

Hmmm, as I wrote the above, I realized that this intermittent problem only seems to happen after the engine is warmed up. When I came home last night after my meeting and the bike ran fine, I stuck to 60kph streets and it was colder outside. Maybe temperature is a factor. I found this link on the IBMWR site last night after I posted:
Intermittent Engine Cutout Problem Solving
.. and the fellow recommends a bunch of things including the starter and other electrical cleanup, but also recommends heating up the hall effect sensor with a heat gun to see if the engine gives out. I'll try that as well, although I hope that's not it because it require purchasing a new sensor

Thanks again guys! I'll let you know how it goes.

Tony

With the bike stationary on the centre stand, turn on the ignition and turn the bars from lock to lock and see if the ignition lights go out.

On my K75C, one of the wires leading up from under the tank to the instrument cluster had broken internally and the bike would stall whenever I turned bars to the left, but would be OK when looking straight forward. Unlikely, but a simple check to test the integrity of those wires.

And if it is the Hall effect sensors ..

http://www.jaycar.com.au/productView.asp?ID=zd1900

Zitat von "wongstein"

Thanks guys!

Rene, I read somewhere that BMW does some funky routing of electrical paths through the starter, so what your saying makes sense. So that'll definitely be part of the electrical cleanup which is my next step.

Yep, there is a load relay. Its primary function is to shut down power to all systems except FI and ignition during starting. A good move to drop lights and other things when the battery is driving the starter. This however should not kill the running essentials like FI and ignition, but who knows.

Zitat

People say that the computers are dead-reliable, but I...

Please tell us the year of your K75. I don't know much about 75s but you possibly don't have a computerized system (Motronic). It can make a difference.

Zitat

...stuck to 60kph streets and it was colder outside. Maybe temperature is a factor. I found this link on the IBMWR site last night after I posted:
Intermittent Engine Cutout Problem Solving

Pure pearls of wisdom... he is absolutely correct. I for one, have a tube of Vaseline handy and whenever I see a plug or a plug connection, I unplug it, give it a clean and fill it with Vaseline and put it together again. Do this will all connectors (including the FI and ignition module big plugs). This will ensure dry reliable connections. The "computer plug" should seat with a positive click and look fully seated. If you work your way through most of these chances are that you may solve the problem, at least, you will exclude a large complex component and can concentrate on individual things like sensors.

Look at the ignition switch and clusters of connectors under the tank. If they are hard to unplug, look for signs of corrosion and spray them with the appropriate electronic spray with lasting residual repellent oil.

The list provided, it is a good method to fix/prevent intermittent problems. Good luck.