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1990 K75S died suddenly

K100RS 85 w 147k mi. NAPA CE-1 Stabilant 22 keeps mine going more than anything else

Dear Sudden K Bike loss of power or loss of even more,

I've "Q tipped" many low millivolt type connectors and many 12v connectors over the years with NAPA CE-1 Stabilant 22. You hear a little sizzle of the corrosion being obliterated, put the connectors together and things run better, same computer, same hall effect sensor(s), same fuel injectors, same fuel pump as new. The eye dropper bottle cost just shy of $100. It was the best $70 I spent almost 10 years ago. Mine would cut in and out, die, sputter etc. then I started using this on the K1 connector first. I have not need a tow yet. Did buy some new relays and brake light switches.

A different motorcycle had an intermitant start one day last summer, turns out the battery connector had jiggled loose. Wires that are almost broken through can do this too, they might be near the steering triple clamp because those wires take a beating and can be routed well or poorly causing a wide range of "lifetime."
 
Thanks for that input 075038 (if that is indeed you real name:whistle). I am thinking along the same lines that you are. It's a b@$t@rd little wire somewhere that's shorting out or broken or...

I just got back from a stint of troubleshooting. I hooked up my timing light to lead #3 and cranked the starter. The strobe is strobing so, at the moment, it will be impossible to diagnose a fault.

Over the next several days I will be checking and cleaning every connection I can find as I reassemble the bike.

For instance - I could see that the primary ground is pretty corroded. I checked continuity between each of the wires and the frame though - and they all check out ok.

Nevertheless - I will take it all apart and clean it before reassembling.

Untill it fails - I can't really find the fault. I plan to ride it around the neighbourhood (all uphill of my house) for a full day and hope it fails....then go from there.
 
Jasper - it's getting late (about 1:30AM here..) so tweak me tomorrow and I'll give some more thought to it.

Quick thoughts: If you are seeing loss of BOTH injection and ignition - the common failure point starts at the HES and works it's way up through the ignition module. The L-Jetronic gets it's trigger off the ignition module (which is triggered by the HES,) so it isn't likely to be at that end. If I had to guess, it's between the HES and the ignition module (located under the tank bolted to the frame right behind the steering head.) I would be looking very carefully at the wiring between the two (assuming your HES test was conclusive.) And Stablant-22 IS very good stuff. The tiny 10cc bottle will last the rest of your life, so the cost isn't all that awful. I talked NAPA down to around $45 for mine, but that was at least 15 years ago..
 
In the past, I've had my K100 just die a few times while riding. My problem was much simpler than yours most likely is. Feel free to disregard it. On a few occasions, while riding over a rough road, the key in the ignition moved and shut off the ignition. That ignition assembly has since been replaced. With the new assembly, I've also had the bike simply shut off while riding. Problem, with my bike and bar risers, the tank bag sits closer to the keyed ignition and the bag and key have occasionally touched and turned the bike off. I'm certain that your problem is more complicated than mine, but just thought I'd give you a scenario that had a bike running and then turning off, and of course, starting right up again. Best of luck narrowing down the problem.
 
In the past, I've had my K100 just die a few times while riding. My problem was much simpler than yours most likely is. Feel free to disregard it. On a few occasions, while riding over a rough road, the key in the ignition moved and shut off the ignition. That ignition assembly has since been replaced. With the new assembly, I've also had the bike simply shut off while riding. Problem, with my bike and bar risers, the tank bag sits closer to the keyed ignition and the bag and key have occasionally touched and turned the bike off. I'm certain that your problem is more complicated than mine, but just thought I'd give you a scenario that had a bike running and then turning off, and of course, starting right up again. Best of luck narrowing down the problem.

This was the first thing I checked - actually I checked the the kill switch - but it is effectively the same thing here.

My thing is that when it fails - ALL of the lights on the dash stay on.

If it was the ignition switch - or the kill switch - or a battery lead - the lights would go off.


I'm thinking along the same lines as Don. It's the HES or the ignition box - or the connection between the two.

The HES test was pretty conclusive....I could not get it to fail on the bench no matter how hot I got it or how much I jiggled the wires. Of course, the problem is intermittent so I can never be 100% certain - again there's the painful part of this.

Also - I don't know conclusively that the fuel stopped. I only think it did. I didn't have a chance to check it when the failure was occurring and it hasn't happened again. What I observed was:

1) No fuel smell out of the tailpipe while cranking the starter while the failure was occurring.

2) No fuel fog blowing out of the spark plug hole while cranking while the failure was occurring.

3) Yes fuel fog blowing out of the spark plug hole while cranking while the failure was not occurring.



If I am getting neither spark nor fuel then this suggests that:

1) The HES is telling the ignition box that the bike is not running, or

2) The ignition box isn't getting 12V, or

3) The ignition box isn't getting ground, or

4) The HES is not getting 12V from the ignition box, or

5) The HES isn't getting a ground from the ignition box.

If I am getting fuel but no spark (which may be happening, but frankly isn't likely because the ignition box controls the EFI) then:

1) The coils aren't getting power to the primary circuits.

It isn't (can't be) a coil failure because there are three coil. The bike isn't stuttering or missing - it' stopping dead, and the three coils aren't all dying at the same time and then coming back to full strength soon afterwards.

They share a power source though....and I'll be checking that as well.

This sure would be a lot easier if the bike was failing reliably. It's all just hypothetical while it is running normally.
 

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Well - not sure what to say.


I haven't had much time to look at the bike over the last few days - I'm working on a Masters degree and I have a fairly significant paper due this weekend. I have work commitments and young children as well. At least my wife is a good woman and the weather is turning nice here. It's not all bad.




When last we met, the tank was off and I had all of the wiring in front of me. The primary ground looked not great - but not catastrophic either. I had a timing light hooked up so I could see if I was getting a spark without having to pull the plug. I was - the fault was not occuring.

Anyway - I spent this morning wiggling wires trying to make the failure occur. I hooked up my timing light and watched it strobe away when I hit the starter button no matter what I did.

I also checked rechecked and checked every single ground wire I could find again and again - mostly on the loom going in to the ignition box. All this while jiggling and shaking and pulling on the wires.

The strobe just kept strobing away like there was no problem at all.

So then - I bring out some long hoses and hook up the fuel tan on a bench next to the bike (see the photo). Plugged in the tank and started the bike.

I ran it like that for 30 full minutes. At one o=point I measured a water temperature saw 80 using my infra-red pistol.

So I took out a a socket and ratchet and started loosening the ground bolt - just as the electric fan came on by coincidence (red herring).

I got about three turns out when the bike died.

I tightened the bolt again - and it wouldn't start! Could that be it?

I checked for ground at the loom to the ignition box (there are two) and they checked out fine....ok.

Nevertheless - I disassembled the ground screw and the five wires that are attached there. I cleaned every one with 220 grit and reassembled the whole thing with conductive paste. I hooked up the strobe - I'm getting spark.


Here's where it gets stoopid.

I put the bike back together again - I install the tank and the fuel lines and the vent lines and I plug in the fuel tank. I'm going to take a ride right?

Nope - I go to start the bike and - no fuel pump whine, no start.

I hook up the strobe - *NO SPARK* OMFG !



So I pull the tank off again - this takes a few minutes - and try the strobe again - and sure enough I HAVE SPARK again.!!

SO I check to make sure I'm not pinching any wires - I'm not - and I put the tank on again.

This time it starts and runs fine.

I just finished riding it around my neighbourhood for 20 minutes and it didn't skip a beat.


I don't know guys. It's driving me crazy.
 

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Eureka

Ah - the eureka moment. Gotta love it.

The bike had been running fine for a couple of hundred miles but tonight it stranded me again....in waning light and without tools since I'd stopped carrying them around everywhere just last week.

It started once right after it failed - but died again real quick.

I lifted up the tank and got my hand under there and wiggled wires while I tried to start it - no dice.

Then I started wondering if the fuel pump was running or not - it's hard to tell with all the noise so I decided to unplug the tank and listen for the *absence* of a whirring noise.

You know what - it fired up and burbled for me! With the tank unplugged ! Obviously I was getting spark at that point.

Then I plugged in the tank - it fired up and I rode it home.


****

So - Apparently a fault in the fuel system *will* cause a lack of spark. Not sure what the feedback loop is there.

I'm going back up and reading the threads on the fuel sender. I can see that the wiring for the fuel pump goes through it.

Could it be the fuel pump relay or the fuel injection relay guys?

It seems the system reset itself once that plug was disconnected.


I think I may have this thing beat - good thing too I've been looking and thinking about another bike and that would be a drag because I genuinely like this one.


Will report back.
 
The fuel injection relay's coil appears to be grounded through pin 7 of the ignition unit. So, it seems plausible that a fault with the relay or that leg of the wiring could cause the loss of both fuel and spark.

Edit: Of course, following that circuit a little farther -- the fact that the FI relay coil is grounded through the ignition box also means that a fault with the ignition box ground could prevent the FI relay from activating, so you may well be on the right track already.

What "conductive paste" did you apply to the ground terminals? (Not dielectric grease, which is the opposite of conductive, right?)
 
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The fuel injection relay's coil appears to be grounded through pin 7 of the ignition unit. So, it seems plausible that a fault with the relay or that leg of the wiring could cause the loss of both fuel and spark.

Edit: Of course, following that circuit a little farther -- the fact that the FI relay coil is grounded through the ignition box also means that a fault with the ignition box ground could prevent the FI relay from activating, so you may well be on the right track already.

What "conductive paste" did you apply to the ground terminals? (Not dielectric grease, which is the opposite of conductive, right?)

Thanks James.

I used a conductive paste designed specifically for the purpose. It's similar in appearance to copper anti-seize. I am aware that dielectric grease is not conductive.

I am sure that the ground wires to the ignition box are good. I hope that the ignition box isn't the source of the problem ($1400 from BMW)- but I don't think so given the intermittent nature of the problem.

***
I'll be checking relays and the wiring through the sender unit into the pump.

Hopefully I'll be able to *find* the fault.
 
That conductive paste does sound interesting, then, especially given the common failures of ground points on these bikes. Does it have a name, and is it widely available?

I asked because it often seems as though more people than not mis-use dielectric grease for precisely this purpose, when its purpose is precisely the opposite.

It still sounds like a connection problem. I have something perhaps similar going on, but more intermittent. The two times it's happened I've torn a bunch of stuff down, vigorously cleaned connections and replaced candidate parts. The first time it got fixed for 2500 miles; the second for several hundred miles now. The second time I didn't replace any parts, just went through a lot of connectors (and the ignition) with q-tips and a lot of DeOxit. Something appears to be fixing it; darned if I know what it is.

If you could monitor power at the FI relay in real-time so you could see what's happening when it fails, that would be helpful. If I have to keep doing this I'll likely set up some diagnostic LEDs to show when power is flowing or not. My issue has only happened when in motion, so I can't stop and check relays.
 
I went through HECK with my K 1100LT

I set the testers, probes, meters and all my own theories aside and tried something I hadn't yet.

I had the fuel pump and fuel sending unit outside of the tank sitting on an old pair of jeans with the fuel level arm sitting at about a half tank. I then powered up the bike as though I were going to start it, no fuel pump and no fuel gauge. I'm on the Gremlins tail. I grabbed the four pin connector and twisted it all around and watched the fuel gauge jump from empty to full but still no fuel pump. Note worthy it is that I had jumped the side stand switch and the gauge flipped from full to empty.

I replaced the four pin connector for the sending unit with male and female GM style water proof connectors and the bike has ran fine without even a hiccup since that simply repair.

Have you ever sat behind an automobile towing a boat and trailer and wondered why the tail light on one side dims or goes out when the brake lights light up? Its a bad ground, not a complete ground disconnect but one bad enough to let low amperage work but when you ask for additional amp flow like a brake light or a fuel pump to use the ground it just isn't good enough to do the job.

Replace the four pin connector with suitable replacements(not a trailer connector)and you very well save yourself some cash and lost sleep.
 
Hi James;

I remember reading your thread on this a week or so ago. It does indeed sound like a similar problem.

What gets me is that I have no spark and no fuel. This points to my HES - but I tested those and they checked fine. Then...last night I made the problem go away by unplugging the fuel tank (the eureka moment).....which doesn't point to the HES at all.

I'm thinking that either the fuel pump or fuel injection relay is failing and unplugging the tank "resets" it. Not sure why or how the ignition is tripped by this, but....

A senior spark at work here read the schematics earlier on and he was dismayed to see that in some cases it was the ground that was switched rather than the power. If this relay is getting stuck it could be grounding out hot wire or breaking a ground to my ignition....who knows.

I'm also looking at the fuel sender. The wiring for the pump goes through it and it appears to have been the problem for the K1100RS guy in the thread that Lee linked.

I have the tank off the bike, drained and purged. I'll be taking the sender and the relays out and subjecting them to some scrutiny. I have a 12V power supply so will use that to cycle the relays a few times.


Photo of the paste is attached:
 

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I set the testers, probes, meters and all my own theories aside and tried something I hadn't yet.

I had the fuel pump and fuel sending unit outside of the tank sitting on an old pair of jeans with the fuel level arm sitting at about a half tank. I then powered up the bike as though I were going to start it, no fuel pump and no fuel gauge. I'm on the Gremlins tail. I grabbed the four pin connector and twisted it all around and watched the fuel gauge jump from empty to full but still no fuel pump. Note worthy it is that I had jumped the side stand switch and the gauge flipped from full to empty.

I replaced the four pin connector for the sending unit with male and female GM style water proof connectors and the bike has ran fine without even a hiccup since that simply repair.

Have you ever sat behind an automobile towing a boat and trailer and wondered why the tail light on one side dims or goes out when the brake lights light up? Its a bad ground, not a complete ground disconnect but one bad enough to let low amperage work but when you ask for additional amp flow like a brake light or a fuel pump to use the ground it just isn't good enough to do the job.

Replace the four pin connector with suitable replacements(not a trailer connector)and you very well save yourself some cash and lost sleep.

Hi Zeff;

You figure just replacing the plug might solve my problem eh?

Can you confirm if we had the same symptoms? No spark *and* no fuel?

That's still the part that's killing me. Why would a bad ground to the fuel gauge/fuel pump cause me to lose my spark....and just as curiously - why would unplugging those systems cause me to get my spark back?


thanks!
 
I replaced the fuel tank plug with a Delphi Weatherpack connector the first time I "fixed" my issue, and until it recurred I believed that connector was the most likely item to have solved it. And that may be true - the recurrence may be some other fault that happens to have similar effect. My next guess if it happens again is the soldered ground connection to the outside of the fuel sender.

Yes, several areas on the bike switch ground to complete a circuit. Fuel injectors are another one.

Jasper, thanks for the photo of the Kopr-Shield. I'll have to pick some up.
 
Even with a bad fuel pump, fuel filter, fuel pump connector, etc, you should still get spark at the spark plugs. If both are missing you need to look at the HES and the LJetronic, and all of their coneections to make sure they are clean and tight.
 
Paul Glaves is correct!

EFI and Bosch Motronic Fuel injection stuff is very tricky and when its linked to your ignition system it gets trickier. The K 1100LT that I finally fixed with a new four pin connector was brought to the local dealer with a crankcase full of gasoline. From that one would assume it had weak or no spark and a fuel injection system that just died. I replaced the pressure regulator, fuel lines, filter and had the valves checked for adjustment. I tossed in an odessey battery but still had issues so I ran a ground wire from the fuel tank sending unit mount to the battery negative cable and the bike ran fine for a while.

The bike left me pushing about halfway through an 80 mile test ride. Yup I had a cell phone and a wife who just enjoyed a good chuckle.

I replaced my Hall Effect Sensor (it was the original one) but that didn't fix the problem. Like I related in my analogy with the car, boat trailer and misbehaving tail lights you can have good voltage and an OK ground for tail lights but when you crank up the amp draw(with a fuel pump or ignition coils) and have a bad ground circuit something might just give. Likewise if you have less than great battery voltage(how many ABS units got tossed because of crappy batteries?) I remembered some of the odd ball problems that bad grounds & low voltage cause and just how screwy Bosch fuel injection can be(7.5 years as an MB tech) if its voltage and ground circuits aren't perfect.

I would go for the cheapest and easiest problem to eliminate if I were you, make sure your fuel tank sending unit is good to go and then replace the four pin connector(male and female sides) and give it a shot. Replace it with a quality weather proof connector or connectors, get it out of the way and then if that doesn't fix it go from there.

Regardless of what is really the problem with the K 75 if you have the original and proven to be suspect Hall Effect Sensor then at some point in time you should replace it if for no other reason than piece of mind.

One thing about the Bosch F/I computers for all the generations(jetronic, Motronic and all those other tronics), they are pretty solid and reliable, a lot of dealers and independents tossed good ECU's for no reason other than "they couldn't fix it" or "that F/I stuff sucks" and the "its the computer" diagnosis when all they really had to do is go to the basics of electrical diagnostics & repair.

Heck I'm an illiterate genius and I ignored the obvious with my challenge.
 
Even with a bad fuel pump, fuel filter, fuel pump connector, etc, you should still get spark at the spark plugs. If both are missing you need to look at the HES and the LJetronic, and all of their coneections to make sure they are clean and tight.

I agree Paul - I *should* be getting a spark ...but I am not.

The problem is extremely intermittent and does not appear to be related to heat. I am pretty sure it isn't the HES - I've tested these by the book. I hear what you are saying Zeff - and I may yet replace them but I don't expect this will resolve my issue.

The $64K question for me is why the spark comes back when I unplug the fuel sender/pump connector. Unplugging the tank has fixed my problem twice now. The first time I didn't realize that this is why the fault disappeared, but the second time it was obvious.

This question also applies to your idea to replace this plug Zeff. I'm not opposed to the idea but want to know why unplugging it makes the spark come back.

It's also a problem that checking any fault in the wiring requires me to remove the tank which requires me to unplug the tank...maybe I can wrestle the tank off without unplugging it - but the fault happens so infrequently and can come and go even without me touching anything that I'm not very confident I will be able to examine the wiring while the fault is occurring.

Could the FI relay be the source of my problem?

I have it on my desk in front of me with the cover removed and the contacts don't look burned or anything.....and there's still teh question of why the spark would disappear. Could a ground fault be travelling from this relay to the ignition box?
 
OK - deep breath.

I've checked the HES - I haven't checked the connections at the FI computer.

That's next.....but why would this take out my spark and why would unplugging the fuel sender/pump bring the spark back?

Shorting to ground??

Thank you for you patience, support and ideas gents.
 
So I took the FI computer plug apart this evening and inspected the connectors. Each one looks like new and is firmly fastened in the plug. The spades at the computer look good and each one is solid also.

I also took the fuel level sender out. So far it also looks good.

I'm getting a bit weirded out by this.
 
OK, let's take another look at some of the basics. We have an interruption of fuel and spark. We may have an association with the tank coming off and/or being unplugged. We think the HES is fine, and we know the ignition and FI computers are rarely the root cause of any of this. So, where are there common points of failure?

I believe the FI relay might be one. Its coil is grounded through the ignition box. This allows the ignition box to cut fuel if it knows it has no spark. Do we know, conclusively, whether the reverse is true? Might the ignition box cut spark if there's no current passing through from the FI relay? It stands to reason - no need to spark if the fuel pump isn't working. I'm not sure how you'd test this. Since you have the tank on the bench, you might take the relay out, and power the pump directly via a toggle switch as you press the start button. Then the ignition unit would get no signal on the expected FI line, but you'd be pumping fuel. If you don't have a spare handy, you might try wiring in a standard relay of appropriate capacity to see if there's any difference in behavior.

And there's one other I keep coming back to, that I think you might want to reexamine more closely: the kill switch. You mentioned the cluster lights stay on during the fault, and that you'd expect them not to. That isn't precisely accurate.

The general cluster illumination -- the green bulbs, if yours are still stock -- will stay on if your ignition switch is on, regardless of the kill switch position. The distinctive thing about a dodgy kill switch is that when it goes away and comes back, you will have more lights on than you expect -- but just briefly. The bike will do its start-up thing, so you'll have the brake indicator in the center, and the two red lights on the right illuminated (oil pressure and charge). Thing is, they probably won't be on very long, because you'll get your hand and foot on the brake right away when that happens, and once the alternator gets spinning it'll dismiss the charge light; and presumably the oil pressure light will go out when power comes back. When the kill switch faults, it's like the bike has a total shutdown. It's very sudden, as you described it, and the coming back on is also sort of sudden. If this all happens when you're moving, you're basically shutting the engine off and then immediately bump-starting it. It's a very jerky experience.

The kill switch, of course, powers the FI relay coil directly, has a straight line into the ignition box, and directly powers the ignition coils. So a fault on the green/yellow wire that emerges from the kill switch absolutely has the capacity to do something like you're describing.

So, I recommend pulling apart the right switchgear and doing some thorough cleaning of those contacts. The switch also relies on the pressure of one or two very tiny springs to keep the contacts against each other, and if those springs are weak it can cut the current on that wire. (Be careful not to lose those when you disassemble.) Lastly, a fault on that line might not be in the kill switch itself -- it could, for example, be in the nine-pin connector joining the switchgear to the bike's wiring harness. That's under the tank on the right side in one of the two crusty but formerly transparent sleeves. Your observation of a link to the tank connector may have to do with jiggling that connector when you move the tank around. (Or it could have nothing to do with the tank connector. It's likely that when you plugged and unplugged it, you also operated the ignition switch and the kill switch.)

Keep following the circuits. It's more likely to be something simple than something complicated. (Which doesn't, unfortunately, mean that finding it is simple.)
 
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