K75 Trouble shooting / parts suggestions

[tjtraver]

I'm still tracking down an intermittant failure in my 1995 K75. Once it gets really hot ( after approx 30 miles ) , when just riding along at 5-50 mph , the engine will completely shutoff, tach immediately goes to zero. Once I coast off the road , it usually restarts immediately, as if nothing had happened. The bike always runs 100% ( never misses or stumbles ) else it fails entirely. I've reseated all the connectors , to no avail. Flicking ign and kill switches on/off as I coast to a stop doesn't make any difference, so I don't think its them.

Today I had multiple shut downs , with a really bad had series of failures , 3 or 4 within 5 miles. Thinking it may be an intermittant Hall effect , I removed the T shaped cover over it and ran without it the rest of the way home (~75 miles ), and it "only" failed twice more, which I guess is an improvement. I'm going to use the hair dryer method to try and get it to fail .

From the schematic, other than a power failure , the only components what would cause this seem to be the Hall effect trigger or Ignition control module.
Does anyone have known good used units they want to sell or would be willing to lend out so I can debug this beast ?

Any other ideas ? Thanks for any advice ... Todd

[Bruce_C]

Maybe a pinched fuel tank vent of crud in the ignition switch.
Bruce C :)

[CustomSarge]

A big vote for it being a Hall sensor problem, a not uncommon failure. If you can't find one more easily, I've got one you can work with. Until it's swapped out, maybe carry a can of "Mr. Freeze". Good Hunting... <<<)))

[barryg]

If it turns out that the Hall effect is not the problem; it's possible it could be the fuel sending unit coming out of the tank. I had a 87 K100RT that would just stop running at any given time for know reason. I quit riding the bike because I could'nt depend on it. After repeaded checks the sending unit was discovered to be bad. I could move the unit around and make the bike run or not run. Replaced the unit and problem solved. Good luck with solving your problem.

[k75sboy]

I had a similar problem usually when I went over a sharp bump. Turned out to be the 4 y.o. battery that seemed fine

[DonHamblin]

Todd,

My own suggestion would be to make sure you are only working on the exact problem that is causing you trouble. I know it sounds a bit harsh, but with that electical stuff it is easy to mask the real problem with another one.

Learning the hard way that I wasn't as smart as I thought (while I was raising two teenagers I had that pointed out a number of times), I found it easier to make sure I was not going to be fooled by an outside influnce.

So you might want to baseline everything. Check out

Electricial Tune Up (http://www.ibmwr.org/ktech/electrical-tuneup/index.shtml)

and some of the other related stuff on that site.

I am also one of those folks who likes to check the "inexpensive" stuff first. I was able to clean up something similar by cleaning the "kill" and "ignition" switches.

Best of luck,

Don

[DcnDog]

Todd,

Had the same problem on my '87 K100LT. Cleaned all the connectors. Checked the Hall unit. Had a BMW mechanic check the unit. Borrowed a computer off another K100LT. Replaced fuel relay. Replaced fuel level sending unit. Cleaned all switches. Etc., etc. Problem persisted.

Finally replaced engine coolant temp. switch part #61311459197
4000 miles and no problems.

Good luck and God bless,
Dan

[tjtraver]

Thanks for the replies . And link. I will do those items . This problem is a doozy. I've debugged many electrical probs over the years, but this truly intermittant one takes the cake. I've never had something die faster , with no symptoms / warning or pop right back with less hassle than this one. I have already checked and reseated all the main connectors under the gas tank ( and there sure are enough of them !). The bike has a new battery. It usually quits at highway riding speeds cause that's where I spend most of my time ( or try too ) , but has also quit several times when at a stop sign. It quits during straight smooth roads, not when I'm turning the handle bars or hiting bumps or doing anything at all. In fact it's always a surprise when it happens, as I thought I ly let off the throttle or something , but then see the tach at zero. The Oil and battery lights come on when it quits , so it's not losing power. I've flicked the ign and kills switches after the engine quits but is still being turned over by the rear wheel as I coast to a stop ( nary a pop ). Also, if it were the kill switch the starter wouldn't engage ( but it does), when I go to restart it and it takes a couple of times to fire. But as soon as it stops. Give it a second to cool and it usually fires right back up. Plus, I'd think if it had power to all the right places ( it seems to ) even if the coil pack or fuel pump were to go bad, that with the engine still being turned by the rear wheel , that I'd still see some revs on the tach, due to the hall effect creating pulses and ignition control module still sending them to the tach. (Maybe not but a good theory). The bike doesn't look like it has ever seen rain, and none of the connectors showed any corrosion at all. I was thinking it may be a bad fuel pump replay , but I think I still hear the fuel pump when I go to restart ( and it sometimes takes more than one try when it's really acting up ). Anyway , I've purchased a used (known good ) Hall effect and Ignition module at a very reasonable price ( it is downright scary what BMW wants for those parts new !!! For that reason alone I'd be afraid to go to the dealer ), to swap in to debug this beast. If it doesn't fix the problem at least I know with conviction it's not them and they are good spares to have on hand. I agree that simple problems usually have simple causes. But , I want to get this debugged quickly ( and cheaply ) so I can make the rally this year, but won't go if I can't be sure I'll make it there and back, without a bunch of stops along the way. If any of you guys are going to be there , I owe you a beer , and we can "troubleshoot" this some more. Here's a little aside --- I'm hoping that "twos a charm" ...about two weeks ago, my trusty 1990 Volvo 240 with 180k miles which has never given me a moments trouble, all of a sudden didn't start at JFK airport ( talk about a bad place to break down ) right after I got off a redeye from a motorcycle trip from Seattle to Glacier National Park and back with a buddy of mine, me riding his old Yamaha. So I went from really great time , to really crappy time in short order. But anyway, car wouldn't start, turned over, just wouldn't catch. Tried for 30 mins . Wiggle this, giggle that, swap fuses, check the fuel pump fuse. Pull dist cap. Tap the fuel pump relay. Tap the external fuel pump itself with tire iron ( was getting annoyed at this point and running out of options ). No go. Had AAA tow it to a garage. Then before I left it at the garage, just for grins I gave the key a twist. Vroom, wouldn't you know it , it fired right up ! Ran fine. I drove it for a week, no problems. But, but then one hot morning it wouldn't start in front of my house. Thankfully the part finally went truly so I could debug it. Guess what it was ? Yep intermittant rev sensor ( $ 29 ). As opposed to BMW's $470 !!! Thankfully I didn't pay even a quarter of that for the used BMW one. The BMW dealers I spoke to said those parts hardly ever fail , but after I gave them my symptoms they thought it could be a fit. Will keep you posted on my progress. Thanks for reading , if nothing else, this is good therapy for me ;-) Regards, Todd ( and maybe the guy on a Red Yamaha SR500 at the BMW rally )

[tjtraver]

Hmmm ... I'm trying to understand how these parts would kill the engine based on the K75C schematic, but I'll keep them in mind. They are certainly easy to check. I will experiment to see what happens if I just disconnect those sensors (esp fuel lights), to see what they'll do to a running engine.

How long did the engine with the bad coolant sensor , need to sit before you could restart ?

The fuel guage issue seems to be related to bumps or sloshing or something .Though I've never had an indication this was the prob, will pull the fuel cap off, and work / giggle the fuel sending thru full range of motion to see if I can get it to fail.

Thanks for the tips , I wouldn't have thought to look there....

Regards , Todd
( getting to know more about how many ways my K75 could strand me , than I really wanted to ;-) )

[Bobmws]

You mentioned the bike has a new battery. Check that the computer plug is fully seated and the tab is snapped into place. Wouldn't be the first time this has been the cause of an intermittant problem. HTH

[DcnDog]

>How long did the engine with the bad coolant sensor , need to sit before you could restart ?

It would start up within seconds of coming to a rolling stop. It only stalled at operating temp. The best pattern I came up with was the ride home from work. Summer, 18 miles home, it would stall between 7 and 10 miles (some days at almost the exact same spot each day) from work. Note: the bike was not "hot", the fan was not activated. The fan did and does work. One other thing I did when I replaced the temp switch was to clean the starter.

>The fuel guage issue seems to be related to bumps or sloshing or something .Though I've never had an indication this was the prob, will pull the fuel cap off, and work / giggle the fuel sending thru full range of motion to see if I can get it to fail.

The wiring for the fuel pump runs through the sending unit, there is a circuit board involved as I recall. So the bumps and motion aren't really the issues, it is the circuitry. Also the 4 prong connector has been known to be flaky.

[barryg]

When checking the fuel sending unit; check it where it comes out of the fuel tank. The wiring harness inside the tank goes into one unit attached to the metal peice which seals the tank. I was able to jiggle the one electrical line coming out of that unit and make the engine stop running. I know that is a laymans way to diagnose a problem; but that was the only way I could find the problem. Keep trying.

[DcnDog]

Maybe this is pertinent:

"The non Motronics use a double element sensor in the
engine coolant discharge line. One element went to the FI brain. One to
the fan/overtemp light controller. It connected by a plug that pushed
right on the two blades on the sensor."

Found this in the IBMWR archives submitted by Brian C. Maybe if Don E. is monitoring he can elaborate more on this??

[lorazepam]

When checking the fuel sending unit; check it where it comes out of the fuel tank. The wiring harness inside the tank goes into one unit attached to the metal peice which seals the tank. I was able to jiggle the one electrical line coming out of that unit and make the engine stop running. I know that is a laymans way to diagnose a problem; but that was the only way I could find the problem. Keep trying.

Pros jiggle connections too! you do what you can to find the problems, and then figure out what you need to do to fix them.

I have been a field service tech for around 15 years, and I always start with the easiest things first. Many times we over complicate repairs, with the "cant see the forest for the trees" outlook, and feel overwhelmed when you first start. Just think about what is wrong, and then work from the obvious to the not so obvious.

[deilenberger]

Maybe this is pertinent:

"The non Motronics use a double element sensor in the
engine coolant discharge line. One element went to the FI brain. One to
the fan/overtemp light controller. It connected by a plug that pushed
right on the two blades on the sensor."

Found this in the IBMWR archives submitted by Brian C. Maybe if Don E. is monitoring he can elaborate more on this??

I can comment on this, and make one more suggestion, but I CANNOT repond to the last big posting by Todd since there is not a single paragraph break in it, and my eyes just can't make sense of it.

Yes - the temperature sensor has two elements, exactly as described. You can test the one feeding the L-Jetronic brain at the brain itself (lots easier than trying to get to the sensor on most K bikes.) I believe the technique is written up on the IBMWR K-tech pages, with the resistance readings at different tempertures. I'd check it at room temp and then with the bike fully warmed up. If it is correct at those two temps - I'd bet a beer the other temperature/resistance readings will be fine too.

OK - the other suggestion - from the reading of the initial message (which I could read) - ignition switch.

Question for Todd - when it stops - what lights are on in the instrument panel?

Something to try - wiggle the ignition switch while it is still in the run position. Do any of the lights on the instrument panel flicker?

If so - your switch needs cleaning (and you can find detailed instructions with photos on my website http://www.eilenberger.net - look towards the bottom of the page on THE K75S - there is a link to disassembly and cleaning of the ignition switch.)

One other oddball possibility - the starter. If the insides of the starter get dirty enough from carbon off the brushes it can cause the engine to stop, or not start. I can't imagine this being intermittent, but anything is possible since this fault is really an odd one.

BTW - Todd - if you want answers from me - you have to break things up into readable paragraphs with one thought/question per paragraph. I get LOTS and lots of email asking questions, so making it easier for me to answer means I'm lots more likely to answer.

BTW - Brian Curry does not monitor this forum.

[tjtraver]

All ,

* Sorry about the long ramble before.*

I can comment on this, and make one more suggestion, but I CANNOT repond to the last big posting by Todd since there is not a single paragraph break in it, and my eyes just can't make sense of it.

Yes - the temperature sensor has two elements, exactly as described. You can test the one feeding the L-Jetronic brain at the brain itself (lots easier than trying to get to the sensor on most K bikes.) I believe the technique is written up on the IBMWR K-tech pages, with the resistance readings at different tempertures. I'd check it at room temp and then with the bike fully warmed up. If it is correct at those two temps - I'd bet a beer the other temperature/resistance readings will be fine too.

* I have purchased a new sensor. Just to eliminate it as a possibility . It's "cheap" insurance at $30 *

OK - the other suggestion - from the reading of the initial message (which I could read) - ignition switch.

Question for Todd - when it stops - what lights are on in the instrument panel?

* Low Oil pressure and No Charge lights *

Something to try - wiggle the ignition switch while it is still in the run position. Do any of the lights on the instrument panel flicker?
* No variation at all . But I may clean it anyway. I printed out the (excellent) instructions*

If so - your switch needs cleaning (and you can find detailed instructions with photos on my website http://www.eilenberger.net - look towards the bottom of the page on THE K75S - there is a link to disassembly and cleaning of the ignition switch.)

One other oddball possibility - the starter. If the insides of the starter get dirty enough from carbon off the brushes it can cause the engine to stop, or not start. I can't imagine this being intermittent, but anything is possible since this fault is really an odd one.
* The bike only has 17k miles , so would think low probability of significant carbon build up *

[lorazepam]

All ,

* Sorry about the long ramble before.*

I can comment on this, and make one more suggestion, but I CANNOT repond to the last big posting by Todd since there is not a single paragraph break in it, and my eyes just can't make sense of it.

Yes - the temperature sensor has two elements, exactly as described. You can test the one feeding the L-Jetronic brain at the brain itself (lots easier than trying to get to the sensor on most K bikes.) I believe the technique is written up on the IBMWR K-tech pages, with the resistance readings at different tempertures. I'd check it at room temp and then with the bike fully warmed up. If it is correct at those two temps - I'd bet a beer the other temperature/resistance readings will be fine too.

* I have purchased a new sensor. Just to eliminate it as a possibility . It's "cheap" insurance at $30 *

OK - the other suggestion - from the reading of the initial message (which I could read) - ignition switch.

Question for Todd - when it stops - what lights are on in the instrument panel?

* Low Oil pressure and No Charge lights *

Something to try - wiggle the ignition switch while it is still in the run position. Do any of the lights on the instrument panel flicker?
* No variation at all . But I may clean it anyway. I printed out the (excellent) instructions*

If so - your switch needs cleaning (and you can find detailed instructions with photos on my website http://www.eilenberger.net - look towards the bottom of the page on THE K75S - there is a link to disassembly and cleaning of the ignition switch.)

One other oddball possibility - the starter. If the insides of the starter get dirty enough from carbon off the brushes it can cause the engine to stop, or not start. I can't imagine this being intermittent, but anything is possible since this fault is really an odd one.
* The bike only has 17k miles , so would think low probability of significant carbon build up *

Not if it took very short trips, and was started often. It could be a possibility.

[tjtraver]

Just to close out this thread. I replaced the hall sensor , problem fixed. Verified by trouble free 2,000 mile ride ;-)

PS: I never cleaned any connections or switches yet, but will do so later this summer , as the bike got drenched on several occasions during this trip when riding in heavy rain.

[deilenberger]

Just to close out this thread. I replaced the hall sensor , problem fixed. Verified by trouble free 2,000 mile ride ;-)

PS: I never cleaned any connections or switches yet, but will do so later this summer , as the bike got drenched on several occasions during this trip when riding in heavy rain.

Thanks for the update! :clap

The good part about this is everyone gets to learn from it.

Best,