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Thread: 1990 K75S died suddenly

  1. #31
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    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.

  2. #32
    Registered User jwetering's Avatar
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    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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    jasper
    north vancouver

    1990 K75S

  3. #33
    Registered User jwetering's Avatar
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    Quote Originally Posted by 69ZEFF65 View Post
    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!
    jasper
    north vancouver

    1990 K75S

  4. #34
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    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.

  5. #35
    Benchwrenching PGlaves's Avatar
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    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 - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  6. #36
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    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.

  7. #37
    Registered User jwetering's Avatar
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    Quote Originally Posted by PGlaves View Post
    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?
    jasper
    north vancouver

    1990 K75S

  8. #38
    Registered User jwetering's Avatar
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    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.
    jasper
    north vancouver

    1990 K75S

  9. #39
    Registered User jwetering's Avatar
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    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.
    jasper
    north vancouver

    1990 K75S

  10. #40
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    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.)

  11. #41
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    And, speaking of things that are simple - how's the main battery ground? Is it a good, thick cable, or the piddly little 10awg (or thereabouts) original one? Good clean connection on the transmission?

  12. #42
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    On my 91 75RT when the kill switch is activated , the lights in the cluster are off.
    Ron

    91 K75RT ABS

  13. #43
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    You could very well have two seperate problems

    I would replace the four pin connector and eliminate the the possibility of it being your problem. If it works after that I would and your spark returns and fuel pump works then I guess that connector could affect the spark also.

    The manipulating of that connector seems to be a common denominator in the no spark & No fuel issue.

    I would also be prepared to investigate the HES as Paul suggests, its not his first rodeo ya know. That connector could very well carry the ground circuit for the HES.

  14. #44
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    Quote Originally Posted by roncooper View Post
    On my 91 75RT when the kill switch is activated , the lights in the cluster are off.
    On my '87 K75C they're on whenever the ignition is on.

  15. #45
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    Quote Originally Posted by 69ZEFF65 View Post
    I would replace the four pin connector and eliminate the the possibility of it being your problem. If it works after that I would and your spark returns and fuel pump works then I guess that connector could affect the spark also.

    The manipulating of that connector seems to be a common denominator in the no spark & No fuel issue.

    I would also be prepared to investigate the HES as Paul suggests, its not his first rodeo ya know. That connector could very well carry the ground circuit for the HES.
    The HES connects to the ignition box, not the fuel tank connector. No HES wiring passes through the connector.

    The four wires in the fuel tank connector include two fuel-level wires, one of which goes to the cluster, and the other to the "connector for additional instruments," power (from the FI relay, through fuse 6), and ground. If you have a problem with the connector, it is with the power or ground wires. Neither touches the HES or the ignition box. I'm very skeptical of this connector being able to affect spark; if you have a common cause it's earlier in the circuit. If you have a separate spark problem and fuel problem, the fuel component of the problem could well be here.

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