85 K100RS Cutoff Problem

[BrickFlyer]

Hi:

Recently acquired an 85 K100RS and did a fair bit of work on it based on tips I found on this site.  Thanks! After the repairs, it seemed to be running pretty good. Until today when it stranded me twice.  The bike started, accelerated smoothly and seemed to have lots of power when I pulled out of my garage. I did some city traffic driving here in Atlanta, and everything seemed ok until I stopped for a light and when I applied throttle , it bogged down,  lost power and cut off. I can restart it, and it will idle ok at about 1000 rpm, but when I give it some throttle above 1500 rpm  it bogs down again and dies. So I had to push it to the side of the road and wait.

I let it sit for a while- maybe 15 to 20 minutes-and  it then it restarted and I rode off. Again, good power and accleration. But in short order (under 2 miles) I hit stop & go traffic and the problem reappeared. I limped to the entrance to my subdivision and walked home (uphill) and will go back and see what happens in 20 minutes. When I originally bought the bike it did have some intermittent issues like this but I thought I had solved it. Now I'm baffled.

Here's a list of all the things I did BEFORE this problem popped up today:

New crankcase breather hose, changed oil and oil filter, installed all new fuel lines and vacuum lines, new spark plugs, new spark plug wires, new OEM air filter and fuel filter, replaced the radiator fan and the coolant temperature sensor, cleaned and applied dielectric grease to the fuel tank connector and cleaned and dielectric greased virtually every electrical contact I could access. While I had the radiator out I also checked the thermostat and it operated at the ideal temp. Put fresh BMW coolant in the radiator at a 60/40 water/coolant ratio then I filled the gas tank up with fresh premium gas and went for a quick 100 mile highway ride with no issues. The radiator fan kicked in as expected when I got off the highway and idled a bit and so I thought I was in good shape. That was 2 weeks ago.

Any thoughts on what to look at next? Thanks in advance for any tips.

[Scott_]

HES getting hot and failing would be one thing I would check.
In your driveway remove the T shaped cover on the front of the engine and warm it up with a hair dryer and see how the bike responds.

[frankenduck]

+100

Almost certainly a dying HES with those symptoms.

(Hall Effect Sensor - feeds timing pulses to the ICU.)

[BrickFlyer]

Thanks! Yep. That was it.  Blow dryer on the HES recreated the symptoms. I assume I have to replace the whole sensor? Looks like $394 at Euro MotoElectrics for a new one. Ouch. Is that likely my best option for a replacement part?  Not sure I'd want to risk buying a used part for such a vital electrical system component

I have a Clymers manual and it seems to have a good writeup on how to replace it. But sometimes Clymers leaves out key tips. Any lessons learned about replacing the HES that I should know in advance?

[CubPilot]

I spent a lot of time with my LT with this problem.   I bought a used one and installed it, paid lcl dealer to time it and it ran like new for about 1500 miles and started the same thing.   Over on the IBMWR site I found info on the Oil Head pages about rebuilding the plate.   I went here and ordered this:

www.newwarkinone.co

Hall Effect Vane Sensors
P/N 96F1986
MFGR # 2AV54   This is a Honeywell #

$19.53 ea. USD (it takes two)

This is not difficult, I now have and extra one rebuilt hanging on the wall so I'll never have to change it again.
I now have about 3246.3 miles on it and when I took it apart to paint it was going strong.   I also built the timing box and modified a spark plug to hold a dial indicator to do my own timing.   When I took it to the dealer to have it timed it cost me $85.00 and I had the fairings off.

[BrickFlyer]

Super. Thanks! I will get a pair of them and rebuild my HES.  It's up to $21 each ($42 for the pair)  but thats about 10% of the cost of new replacement.


In case anyone else ever needs hall effect sensor components in the future, here is the link to the site that sells the sensor component.

http://www.newark.com/honeywell-s-c/2av54/hall-effect-magnetic-sensor/dp/96F1986?Ntt=2AV54

[frankenduck]

To get the timing right, line up the notch on the HES with the notch where it mounts. (Right side looking at the engine from the front.)

I used to doublecheck it with a timing light but after doing several and them not needing adjustment after eyeballing it I don't even bother with the timing light anymore.)

[BrickFlyer]

Frustrating! I installed the replacement HES unit and still have the same problem. It might even be worse. I had barely ridden 2 miles before it failed again in the same mode so it hardly had time to get very hot. Engine just bogs down and the bike dies. Let it cool for a few minutes, it fires right back up.

 I am pretty sure I swapped HES unit out properly. I scribed a nice reference line, aligned the new HES with the reference line and with a few minor tweaks it was idling and running as well as ever. I took it for an intial ride around my neighborhood just to make sure it wasn't pinging or anything. All seemed good.  (I didn't use a timing light or the suggested BMW LED sensor). I cleaned all the contacts on both parts of the electrical connection. I also zip tied the cables to the frame.

The unit I installed was a used one, but the seller said he had tested it and I have a few days to send it back if it is bad. Is there a simple electrical test I can do to check the replacement HES other than the blow dryer test? I even purchased replacement sensors that I could install in my old HES assembly, and planned to keep that unit as a backup. But the problem may actually lie elsewhere.

Any ideas of other things to check that might cause the same symptoms?  Thanks in advance for any help.

[frankenduck]

A couple of other usual suspects:

Wiggle the connector for the fuel pump.

Ignition switch.   I just fixed a local guy's 86 K75C.  After he spent almost $500 having the dealer look at it (and not figure it out) he had me take a look.  Took me 20 minutes to figure out it was a bad ignition switch.  He emailed me yesterday to let me know that his bike is running great now.

Check all grounds and battery connections too.

[pallum]

It definitely wouldn't hurt to check on the ignition switch. I spent 4 days stranded in Montana looking for a rogue wire short when it was actually just a dirty ignition switch.  ::)

[BrickFlyer]

Thanks. I will check out the ignition switch and the fuel tank connector this afternoon. The fuel tank connector has wiggled loose on me before and I think I am going to upgrade to a better connector even if the problem turns out to be a dirty ignition switch.

[BrickFlyer]

Interesting. I pulled the switch and the contacts looked pretty clean. But I cleaned them up anyway and put some dielectric grease on the contacts. As I was reassembling it I happened to give a gentle tug on the green wire and the whole wire broke off. So I re-soldered all the wires and the bike fired up ok. Haven't had time for a test ride yet. Even if this is not the fix it was a problem waiting to happen!

[BrickFlyer]

Just a quick update on the cutoff issue in case someone else runs into a similar problem in the future.

Well, after re-soldering the wires on the ignition switch I went for another ride and it died on me again. As usual it restarted and I was able to make it home. So at this point I decided to go back through every ground and mating connection, cleaning and tightening along the way. And it appears to have paid off. I had checked and cleaned the big connector to the EFI brain previously and recalled that it was on pretty tight. It took a screwdriver to remove the clip on the side. So was expecting a bit of a battle to remove it.

Instead, when I went to check it this time, the cable pulled off with a simple tug. Clearly the clip on the right had either not been fully latched or vibrated just slightly loose. I also noticed that the little rubber mounting feet were not properly aligned in the track.  So I cleaned the contacts, made sure the cable was tightly connected and slid the rubber feet back in the slot.

Took the bike out for a little 100 mile spin and it ran like a dream. Nice and smooth acceleration, radiator fan kicked on and off when in city traffic and no heat related issues. Repeated the process again today with a 150 mile ride and all was good. While I am sure that the Hall Sensor was at least one of my problems, and the ignition switch wiring was a problem-in-waiting,  it looks like the root cause may have been the darn connector on the EFI unit.

Thanks for all the help and I hope this is useful to anyone else chasing an intermittent cutoff. 
 

[frankenduck]

Thanks for the update.