crankshaft sensor gone bad

[Graf]

here is one more for you guys to chew over..
About 3 weeks ago I started experiencing a brief (less the 1 sec) when going throught the gears in hard acceleration. This was especially bad if you crank the throttle open in 6th gear....the bike would start to accelerate but all of a sudden it feels like the fuel was cut off for a moment (tank at this time is full).....you let the throttle back a little and it's ok...acceleration resumes. I have took the bike to the dealer last week for 12k service and explained the problem to him. After a regular "maybe you imagined it!" question, I assured the mechanic that I was capable of telling if there was something wrong. Here is what the dealer did after performing the 12K service:
1. took a bike to a test ride - found nothing wrong
2. hooked up to a computer - nothing wrong
3. took a bike for a test ride again - finally confirmed the problem exists
4. changed the coils (all) and took it for a test ride - problem still exists
5. found that 1 spark plug was cracked (changed all spark plugs) - problem still exists
6. hooked the bike back to the computer and checked specifically the crank shaft sensor - sensor passed 2 out of 3 times (it finally errored out)
7. they ordered the sensor and received it overnight.
After changing it, the problem was solved.
Cost of 12K service at BMW of SF is $450 + $30 for spark plugs (no labor was charged) = $480.
Did any of you experienced similar problems with your bikes?
thx,
Alex

[Mollygrubber]

I experienced something similar yesterday, but I wrote it off to the ASC kicking in, as it was quite cold out and I thought I hit an icy spot.

However, I didn't notice any ice (and I was looking, I can assure you). I'll keep this in the back of my mind in future - gosh I hope builtforcomfort doesn't get wind of this...

Thanks for the heads up!

[celticus]

Alex, At what RPM does this happen? Always at the same RPM? If you open the throttle less abruptly does it still happen?

Mark

[tinytrains]

My 1988 K75 developed a sensor problem years ago. I would start it in the morning, and after 8 minutes exactly, it would shut off. Hit the starter and it would re-fire. Replaced the sensors and it has been fine since.

Scott
1988 K75
2009 R1200R

[deilenberger]

My 1988 K75 developed a sensor problem years ago. I would start it in the morning, and after 8 minutes exactly, it would shut off. Hit the starter and it would re-fire. Replaced the sensors and it has been fine since.

Scott
1988 K75
2009 R1200R

Just one quick comment - I believe it was likely the camshaft sensor that went jumblies up in this case. AFAIK, the hexhead engine doesn't have a crankshaft sensor.

It's #14 on: http://www.realoem.com/bmw/showparts.do ... g=11&fg=20

Your failure was the imfamous hall-effect sensors failure on the K series bikes. Fairly common, and a thermal fault, which is why it shut down when the bike warmed up.

The camshaft sensor should be a much simpler device - a simple reluctance (magnetic) pickup that detects the steel lump on the end of the camshaft at TDC. They used to fail on BMW cars with some regularity 25 years ago - after about 1990 it was very rare to have one fail. They are a very simple device (coil of wire wound around a core..)

Anyway - unless I hear of a rash of failures, I won't be looking to add it to my spare parts quite yet.. I do have spare coils, and EWS ring, and haven't needed a thing, proving Eilenberger's Law of Spare Parts.

[Graf]

Alex, At what RPM does this happen? Always at the same RPM? If you open the throttle less abruptly does it still happen?

Mark

it usually happned around 5-6k rpm.....and only under hard acceleration

[tinytrains]

Ok. I did not realize the sensors were that different on the R's from the K's. The title was crankshaft sensor, so I went with it.

Scott