Hey there,

This is a little long, I know, and sorry!

So I originally had an engine cutout problem where I would be riding, the engine would randomly cut out and then come back on a couple seconds later. This I eventually narrowed down to the right side on/off + start switch unit. So, I replaced that switch with a good-working one I bought from ebay. In the course of all this, the bike had been sitting for about a week. I also had a small 3/4" block of wood under the left side of the center stand just to keep oil from seeping in to the combustion chamber.

So anyways, I swap out the switches, put it all back together, go to start it, and have a rough time getting it started. Battery is brand new and fully charged. I figure it's probably just due to it having sat for a week or so, and try it a bit more. On the ~7th try of starting it, it finally started. It was acting normally, and seemed fine. The switch worked and was much better than before.

I revved the bike up to about 4-4.5k rpm, and then it suddenly just stopped. It just shut off. So I tried starting it again. The engine turned over, and I could see a little exhaust coming out the pipe. This is the current state of the bike. The starter turns for about 2 seconds, then the engine just turns maybe at 100 rpm for a half a second then it all just stops. It's like the starter starts to start the engine, but then quits before the job is done.

The odd thing is that the engine will do more revolutions if I don't hold the choke on or pull on the throttle. When I hold the choke on, most the time the engine doesn't turn at all. I checked fuel flow by removing the hose from the rail, putting it in a jar, and pressing the starter button. A pretty good amount of fuel came out, so the issue is not with fuel delivery.

Next, I pushed it up a big hill (ugh!) and then coasted down trying to essentially jump start it. Ignition and on/off switch on, the engine started turning (of course, as a result of the rear wheel turning), but the fuel pump did not come on.

Cleaned all spark plugs (they're new, and there is spark because of the exhaust I saw coming out of the pipe each time I tried to start it). Same issue after cleaning.

At this point, I took it to our local motorcycle shop specializing in BMWs. I actually saw a couple k100s in there, so it's nothing new to them. The mechanic used the initial two hours of labor and called me up. He said he checked all the simple stuff, such as fuel flow, airflow meter, air leaks (there quite a few, but they never stopped it from starting nice and strong before), connections, fuses, etc etc. He said he was pretty stumped and that to get the bike to good running condition, it'd be around 1200-1500 USD (hah! yeah right). He suggested that it could be a computer issue, either the ICU or the EFI. This made the most sense to me as it seems like the computer may be telling the starter that the bike is at 700+ rpm when in fact it's not, causing the starter to quit and the bike to not start.


Does anyone have any further insight and suggestions, or can anyone justify my spending $150 on a new (used) ICU as a strong possibility that that's where the issue is?

If your starter just quit after a few seconds, it sounds like a hall sensor ground problem.

Rene Z did have this problem a few weeks ago.

That was one of the things the mechanic said he checked was making sure the Hall Sensor was in good shape and correctly connected.

If you got this problem I have in mind, your starter would go on-off-on-off
within a few seconds, as long you hold the starter button pressed.

Yeah, if I hold the starter buttons, the starter will turn 3-4 times, then stop, and if I continue holding, it will come back on and do the same thing after a couple seconds, then again, etc etc. Does this mean something?

Seems like your mechanic didn`t check good enough, both on the other hand this fault isn`t that obvious.

You`ll have to change the hall sensor unit, or the hall sensor elements...if you are a bit handy (much cheaper).

I`ll see if I could find back to the earlier mentioned thread.

Here you got some reading, that would keep you occupied the next XX minutes.

Awesome! I'll read up on all that when I get out of class later and then do some work in the next couple days when I've got time. Thanks a ton!

Inge K. wrote:If your starter just quit after a few seconds, it sounds like a hall sensor ground problem.

Rene Z did have this problem a few weeks ago.

I'll second this opinion. Tricky little bast#@ds.

CF

The symptoms are very much that the Hall sensor is stuffed it just goes to show how little you can rely on bike shops to do any diagnosis of a problem, just throw parts at the bike till it goes and send the poor owner the huge bill. There are exceptions to that like Anton and Rubber Chicken racing garage, those guys diagnose, define the issue, fix the issue and charge no more than that cost.
Regards,
K-BIKE

YES! You guys are all awesome. Got a tested / working hall sensor from ebay for ~$100, installed, runs just like it did! Awesome awesome awesome! Now I can list the thing again to sell it so I can pick up that 1992 k100rs i've been eye-ing for so long

Thanks a ton all, i fixed it and i learned from it. Gotta love it.

Good news Rabidchiwawa007 (sure is a mouthfull) now on to that 92 RS which sounds great, the 16v are a great model.