Electric Mystery

[Pstokes]

Hi All,
I have an elctrical problem that I could use some help with, please.
My bike is a 93 K75s with about 46,000 mi. (I am, I believe, the third owner). What is happening is when the bike warms up while riding and I come to a stop at a light or sign and pull in the clutch, it tries to die, wont idle. This has left me on the side of the road twice now, once a loooong way from home. This is when it went to the shop and got new brushes and I thought all was well.
The other day I took a short ride 10-15 mi and it was acting up again on the way home, but I made it to my driveway where it died when I pulled in the clutch to go over the curb. I tried to re-start, but just got a "click". My driveway is uphill, so I left it at the bottom and went in to the garage. About 20-30 mins. later I went down to start pushing it up. I tried the starter again and it started fine. I can go out and start it now even though I haven't hooked up the battery tender yet.
On the last ride, I got no indication of a problem like before the brushes were replaced, like backfire or flashing abs light. My BMW battery is also fairly new, about 6-mos. old, and stays on the Tender if I don't ride.
Unfortunately, I'm not real good with electrical, and I'm quite a ways from a shop that might be able to help. Any advice would be greatly appreciated, or if there is already a thread that adresses such an issue, could you direct me to it please?
Thank You All Very Much,
Paul

[sgborgstrom]

New brushes? Alternator or starter?

I wonder if you have an intermittent short in the clutch switch that is killing your engine. My other idea is that the TPS or ECU is malfunctioning, fuel to the injectors is shut off momentarily when you close the throttle, IIRC it comes back on at 1500 rpm. Maybe fuel delivery isn't resuming when it should.

[brickrider]

I wonder if you have an intermittent short in the clutch switch that is killing your engine. My other idea is that the TPS or ECU is malfunctioning, fuel to the injectors is shut off momentarily when you close the throttle, IIRC it comes back on at 1500 rpm. Maybe fuel delivery isn't resuming when it should

The TPS (Throttle Position Switch) does definitely sound like the place to start.

Brickrider

[Pstokes]

Thanks for the input!
I looked through the Clymer book and I now know (I think) where the tps is located. Now what? How can I tell if it is at fault? Clymer doesn't really address the tps, they just show you where to find it. I get the impression though that it is one of those un-servicable pieces that you really shoudn't mess with.
Is there any way to test this on my own, or should I try to get it to a shop (none close). It seems to work ok close to home, but as it gets further and warmer, the problem becomes more noticable until it dies on me.

Thanks,
Paul

[deilenberger]

I can't see any reason a TPS would fail progressively with temperature.

What will fail like that is the hall-effect-sensor. If this is the case - you are out of your league on it, and a shop is where you'll need to get the bike. Typical failure mode of the hall-effect-sensor IS thermal in the beginning - as the bike heats up it starts failing and one or two cylinders will intermittently cut out. When the bike cools off - things get better again.

To test it you'll need a hair-dryer and a set of metric allen wrenches.

Here is how to test - if you're not comfortable doing this - find someone who would be:

- Remove the "T" shaped metal cover on the front of your engine (right side - front) - this reveals the Hall-Effect-Sensor mounting plate.

- Start bike

- Put hair-dryer on hot/high - and blow it at the HES mounting plate. Let it go for a good 10 minutes if necessary.

- If the bike starts to miss, or run rough, or stalls - chances are excellent the HES is going bad. If so - continue by:

- Put hair-dryer on air only (no heat) - blow it at the HES. If the engine smooths out, or can be started again - you've confirmed your HES is at fault.

Bimmerboneyard sells replacement ones and I believe MotoradElectrik does also. If not - a dealer can get you one. Replacement involves re-timing the engine, something not that easy to do at home, so you may want to get a dealer involved (they have the special tools to do this..)

HTH!

[98lee]

If it is only dying when you try to let the bike idle after it is warmed up (at a stop, clutch in), it is also POSSIBLE that the culprit is exhaust valves that are way too tight. One of mine developed those same symptoms right after I bought it. It just needed a valve adjust.

Check Hall effect sensor first.


The only thing that doesn't match either of these causes is the "click" you got when you tried to restart it.

That sounds like a low battery with a bad charging system??:scratch



:dance :dance :dance

[tjtraver]

I too had a Hall effect on my K75 fail just as described . If you're so inclined , it can be a do it yourself swap. I replaced my failing hall with a used one and rebuilt the old one to carry as a spare . Mechanically it's a real easy swap.

But ...

.. before removing the old failing unit , scribe a mark on the " metal cup with holes in it" that rotates between the hall transistors. Then put a timing light on the engine #1 cyl , start the engine and mark the engine case where it lines up with the scribe mark on the cup.

Next, use a pencil to mark the cases exactly where the failing hall unit is bolted in place. Then replace the failing hall unit with the new one, restart the engine and rotate the plate until the scribed marks line back up . ( Mine were off only fraction of an inch )

This was 10,000 miles ago and it's has been running great ever since . YMMV

Best of luck with it ... Todd