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1Back to top Go down   K75 Weak/No Spark Empty K75 Weak/No Spark Wed Feb 10, 2021 4:57 pm

RetroRebuilds

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Picked up a non running 1992 K75 with a stuck starter relay. When I first got the bike it had no battery, installed a new one but right away noticed the starter was engaging as soon as I touched the terminal. I replaced the rely and it would turn over when pressing the starter button but then only once and then it wouldn't work again until I would unhook the negative terminal, after several attempts at this I noticed the gauge cluster light would all go dim when cranking as well, I unplugged the gauge cluster and then it would crank on demand every time, but still wouldn't start. Here is a list of things I done so far as I have another K75 (running) that I have been swapping parts from for testing.

- Changed Hall Sensor
- Changed Coils/wires
- Changed relays
- Changed temp sensor
- Cleaned grounds
- Check earth continuity to coils
- #1 coil has No spark 2-3 have weak spark
- If I take the 12v lead from coil #2 and put in #1 it sparks but the #1 lead isn't working
- All coils have 12v to them
- Unplugged and check connections under tank.
- This bike didn't look to have any other electrical mods or anything that have been tapped into over the years, it all looked original.
- From past experience it seems like there is a short to ground somewhere that is pulling voltage from the coils?
- Also the top fuse in the fuse box has a dimmer light then the others when testing with probe but still reads 12v.

Any suggestions on what to try next would be greatly appreciated

Thanks

    

2Back to top Go down   K75 Weak/No Spark Empty Re: K75 Weak/No Spark Wed Feb 10, 2021 5:25 pm

Arlina

Arlina
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Change the leads coil - sparkplug, will that do any good?


__________________________________________________
K75 Weak/No Spark Eu-log10  K1100RS/LT - R1200RT - R1100RS (RIP) - Cagiva SST 350 Ala Verde - K75LT project - K75 Schurgers - K75S
    

3Back to top Go down   K75 Weak/No Spark Empty Re: K75 Weak/No Spark Wed Feb 10, 2021 5:28 pm

MartinW

MartinW
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Is your battery fully charged. If it's not fully charged the relay could be sticking and will only release when the earth is removed.
Regards Martin.


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K75s Hybrid
    

4Back to top Go down   K75 Weak/No Spark Empty No go Wed Feb 10, 2021 5:57 pm

daveyson

daveyson
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There's a wire from the tacho to a coil (#1 I think,  haven't got my books) Remove it and plug the cluster back in. If it now cranks with the cluster plugged in, you might have isolated the location of the problem.

Maybe look at the earth's to coil 1 as well.

#1 sparks but #1 lead isn't working? Do you mean #1 HT lead to spark plug? If so that's maybe normal as there is an air gap in the lead.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

5Back to top Go down   K75 Weak/No Spark Empty Re: K75 Weak/No Spark Wed Feb 10, 2021 6:06 pm

RetroRebuilds

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The battery is new and fully charged, currently the gauge cluster is remove and it cranks just fine, still have weak spark. I'm getting 12v to each coil lead so I think those are good and they are ground well.

    

6Back to top Go down   K75 Weak/No Spark Empty Re: K75 Weak/No Spark Wed Feb 10, 2021 6:16 pm

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@daveyson wrote:There's a wire from the tacho to a coil (#1 I think,  haven't got my books) Remove it and plug the cluster back in. If it now cranks with the cluster plugged in, you might have isolated the location of the problem.

Maybe look at the earth's to coil 1 as well.

#1 sparks but #1 lead isn't working?  Do you mean #1 HT lead to spark plug? If so that's maybe normal as there is an air gap in the lead.
Not getting any spark out of the #1 coil, I'm getting 12v to all the coil leads, I can swap the #2 coil lead to #1 then I get the same weak spark out of #1. Is the ground sent from the ICM which which makes the coil active/spark? I've even swapped that out and no better results. Still think there is a short to ground somewhere, maybe the coil signal wire from coil #1 to the cluster? Should I just remove that at the coil for testing?

    

7Back to top Go down   K75 Weak/No Spark Empty No go Wed Feb 10, 2021 6:29 pm

daveyson

daveyson
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Yep,  that would be a quick easy way. If no difference maybe unplug the other end as well.

And yes, the computer controls the coils.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

8Back to top Go down   K75 Weak/No Spark Empty Re: K75 Weak/No Spark Wed Feb 10, 2021 7:57 pm

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Correction... Only getting 10v to the coil leads when testing the connections, if I take the negative probe from the reader and touch the battery ground I get 12V. Seems like a bad ground to the coils? but doesn't the ICM send the ground, if so how do I test the strength of the ICM ground?

    

9Back to top Go down   K75 Weak/No Spark Empty Re: K75 Weak/No Spark Thu Feb 11, 2021 7:07 pm

cycleman

cycleman
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The #1 fuse is known to cause issues, replace it and see what happens.

    

10Back to top Go down   K75 Weak/No Spark Empty Re: K75 Weak/No Spark Sat Feb 13, 2021 8:36 am

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SOLVED: Ignition switch was faulty causing short to power. Thanks for all your input.

    

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