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Rabidchiwawa007

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Hello,

The bike is a 1992, 16v, K100rs

So, the cooling fan was working just fine, but the thermostat was pretty inconsistent, so I got to working on it. I replaced the thermostat with one rated at 82 celsius. When I'm moving, all is well, the cooling system works great. As soon as I stop, the fan does not come on and it starts getting hot.

During that process, I flushed the cooling system and cleaned out the pump as well. I got it all back together and that's when the stopped coming on.

-I checked to make sure the fan works. It's a little squeaky when it first comes on and goes off due to drying bearings, but it turns just great. I simply ran wires from the battery to the fan connector and it came on.
-The fact that the fan came on when I did that shows that the connections directly on the fan are fine.
-I checked to make sure the connectors to the water temp sensors were connected and not corroded, all seems well.
-The temperature gauge and idiot light both work as they should, which makes me think the water temp sensors are fine, but I could be completely wrong in that assumption.
**Edit: -all the fuses down the side of the fuse box are in good shape.

Any ideas? Thanks in advance!


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1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

Inge K.

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Since your warning light functions, the problem most probably is the relay or
it's connections.

But a easy check to rule out a missing signal from the motronic unit.........
disconnect the multiconnector and ground contact #16...
or jump #5 and #16.
if the fan then starts...the problem is at the motronic unit.



If not next step would be to enter the relay box, and check the relay and it's
connections.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

Rabidchiwawa007

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I was reading around on the forums a bit more and found some tests for the relay.

I grounded unplugged the connector to the temperature control relay about half way and then grounded Pin "58E" to the frame. This did not make the fan come on, but burnt out fuse #2 (counting from top, down). Same result when grounding Pin "58A". The other pins did nothing when grounded. Taking a look at the Motronic connection now as well, per your suggestion!


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1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

Rabidchiwawa007

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Do I ground pin 16 and then plug it back in to the motronic unit, or do I ground it and leave it unplugged?

(leaving it unplugged and connecting pin 5 and 16 together results in the fan NOT turning on.)


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1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

Inge K.

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Remove the relay and jump contact 30 and 87, if the fan starts..........
the problem is a bad relay, or a open signal circuit from the motronic unit.

If the fan don't start...check if you got 12V+ at contact 30 and 86,
and that you got connection from contact 87 and the fan connector.

30 & 86: 12V+
85: ground signal from contact #16 at the motronic unit.
87: Relay output to fan.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

Inge K.

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Rabidchiwawa007 wrote:I was reading around on the forums a bit more and found some tests for the relay.

I grounded unplugged the connector to the temperature control relay about half way and then grounded Pin "58E" to the frame. This did not make the fan come on, but burnt out fuse #2

Then you have been at the BMU relay, and shorted the park/tail light circuit.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

Rabidchiwawa007

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You know what, I flubbed on my first test of the Motronic unit. I still had the fan unplugged Embarassed . I plugged it back in and then grounded Pin 16 on the Motronic connection. Fan came on strong as ever. Is this concrete evidence that the Motronic unit is the culprit and needs replacing? Sad


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1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

Inge K.

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Sadly enough it seems to be the problem, if both connector and pin #16
is clean and free of corrosion.

But another solution would be to ground the relay coil via a switch,
and turn the fan on manually.
Under the relay socket you should search a blue/yellow wire, tap into it and
add the needed length of wire and a switch.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

Rabidchiwawa007

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Boooooo. A new (probably used) Motronic unit is somewhere moderately far in my future then.

Yeah, I just wired the fan directly in to a switch I added to the dash. Good to go!

Thanks so much, again. I wouldn't have been able to diagnose this in a million years with this help. Cheers!


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1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

Rabidchiwawa007

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Quick question in relation to the motronic issue. So it's an issue with the computer itself sending the ground signal to the fan, correct?

While looking around out of curiosity for another unit, I discovered the existence of 3rd party tuned computer chips, and the Harman chip seems like a pretty good, and cheap, investment for my bike.

So the question is: will swapping out chips fix the issue with the fans ground signal as well?


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1968 BSA Lightning
1991 BMW K100RS 16v with K1100LT fairing
    

Inge K.

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You're correct about the motronic unit grounds the fan relay coil.

About the Harman chip, I don't think it would solve your problem.

If I remember correct it was a UK member here which had this chip on his bike.
He wasn't that pleased, and did swap the motronic unit with another member
just for testing purposes.
He reported that the bike was much more nice and smooth to drive with the
genuine unmodded ECU.

If/when you are searching a new motronic unit, be aware that it's two different
versions.....with and w/o a cat.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

AL-58

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The fan on my 1100 has stopped running so in traffic it always gets hot. I've run the Motronic fan test and it runs just fine which shows that both the fan and the fan relay are functioning. Is there anything else to test? I'll be fitting a manual switch so at least I can switch it on when the gauge rises too much and stop any further overheating.

Al


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'87 K100RS/HRD sidecar (1100 motor)sc25
'92 K100RS-16v (Paint it Black)

'87 K100RT with Paralever backend

"When I'm too old and too foolish to handle a sidecar I'll buy a Sportsbike"

    

RicK G

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I put a Harman chip into my K1100 motronic and it was very good at using more fuel without any annoying increase in Horse Power and It would not even run to the rev limiter in any but 1st and 2nd gear. I really do consider that using a potato chip would have been more effective.


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If everything seems under control then you aint goin fast enough:- Mario Andretti
Bikes 1986 K100RT, 1993 K1100 LT, 1994 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 & 1976 SR 500 Yamaha for now
    

Holister

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Maybe it was fried..... Shocked ... 🤡


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1988 K100RT VIN No. 0094680
1989 K100RT VIN No. 0097367 (naked)
1996 K1100RS VIN No. 0451808
Fuel: 95 Octane
Engine Oil:Nulon Full Synthetic 15W50
Gear Box Oil: Nulon Synthetic 75W90
    

AL-58

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My fan problem is fixed, manual switch and it works.

Re the chips; When the 16vRS and K1 were current Staintune released a pipe to suit and also developed a chip for the Motronic to go with it. I used to know a guy that had the combination and he had the proof it worked, better that 20hp improvement on a dyno sheet. I now know that that's early Motronic and the later versions are different. Staintune said they could do nothing with them.

Al


__________________________________________________
'87 K100RS/HRD sidecar (1100 motor)sc25
'92 K100RS-16v (Paint it Black)

'87 K100RT with Paralever backend

"When I'm too old and too foolish to handle a sidecar I'll buy a Sportsbike"

    

duck

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RicK G wrote:I put a Harman chip into my K1100 motronic and it was very good at using more fuel without any annoying increase in Horse Power and It would not even run to the rev limiter in any but 1st and 2nd gear. I really do consider that using a potato chip would have been more effective.

I tried a couple of different chips back when I had one of my K100RS4Vs. (It's 4V, not 16. Read the spark plug cover.) One was a Harman and the other was made by Staintune to go with a Staintune exhaust. Neither chip made a whit of difference to my butt-dyno.


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Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S
14 Yamaha WR250R
http://www.ClassicKBikes.com
    

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