BMW K bikes (Bricks)

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1Back to top Go down   Early 85 K100 Vacuum Switch Empty Early 85 K100 Vacuum Switch on Tue Nov 27, 2012 10:11 pm

ibjman

ibjman
Life time member
Life time member
Both my street 85 K100rs and my parts bike RT are equipped with the vacuum sensing switch mounted on the inside of the fuel rail and plumbed to the vacuum port on the #1 throttle body. I understand that it's signal goes to pin #15 of the Ignition Module. I also understand that it was "discontinued" by the end of the 1985 model year run.
It appears to be an "on/off" switch.
What is it's function? What will occur if it fails or works incorrectly?
I've read a lot of hours in these forums and I've not been able to locate the information. The FI troubleshoot section shows it clearly on pin #15 of the Ignition Module but makes no mention of its values or reasons?

    

2Back to top Go down   Early 85 K100 Vacuum Switch Empty Re: Early 85 K100 Vacuum Switch on Tue Nov 27, 2012 10:25 pm

RicK G

RicK G
VIP
VIP
It changes the ignition timing depending on the load on the engine. Remove it and feed it to a dumpster you will not even notice the difference. You wont get any change in power, torque or fuel consumption. BMW discontinues it because it did nothing.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

3Back to top Go down   Early 85 K100 Vacuum Switch Empty Re: Early 85 K100 Vacuum Switch on Tue Nov 27, 2012 10:52 pm

rosskko

rosskko
VIP
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Hi Ibjman

Have a look at the recent post 'Where does this go?' or similar heading.
Same question asked. Its in the

Too hard. HERE is the link


__________________________________________________
1986 K100RT VIN 0093801K100RT with summer fairing for a northern visitor

Basic/2 6308802K100CJ  05/1988

K1100RS 0194321
    

4Back to top Go down   Early 85 K100 Vacuum Switch Empty OK Thanks but..... on Tue Nov 27, 2012 11:06 pm

ibjman

ibjman
Life time member
Life time member
does anyone really know HOW it functions?........is it a simple on/off switch set at a certain value or does it change resistance with various vacuum readings.
One reason I ask is: if you disconnect & plug the vacuum line, must you also tear the fairing & airbox all apart (again) & disconnect the wire to pin #15?
I appreciate everyones recommendation to "just unhook it" but I'd like to be able to understand it's designed function (even though it proved in effective)

    

5Back to top Go down   Early 85 K100 Vacuum Switch Empty Re: Early 85 K100 Vacuum Switch on Wed Nov 28, 2012 12:15 am

RicK G

RicK G
VIP
VIP
It's a simple on/off switch that turns at a preset vacuum. Best to remove the switch as well and tuck the wire up out of the way which involves removing the fairing. I would just make sure the port on the FI stub is capped and do the rest when you have the fairing off for other reasons as well.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

6Back to top Go down   Early 85 K100 Vacuum Switch Empty Tested it out today on Thu Nov 29, 2012 9:08 pm

ibjman

ibjman
Life time member
Life time member
The Vacuum switch is a N/O switch that closes with the presence of vacuum signal coming from the #1 throttle body (manifold vacuum) test port.

It is calibrated to 0.06 bar to close. I measured it in USA terms & found it closes at 3"Hg. The others are correct that it grounds pin #15 of the ign module.

It has been reported that this changes the ignition timing. It has also been reported that it has no verifyable function on engine performance and was discontinued after 1985.

I would guess that it's designed purpose was to "advance timing to normal (from a retarded start point????) as soon as the engine has any vacuum. Cranking vacuum? I still wonder what was the intended engineering idea of changing the engine ignition timing when the engine drops to less than .06 bar. In my experience.....even cranking vacuum will be higher than that?

Is it possable that the test port vacuum would drop below that point during conditions of W.O.T.

I have not tested vacuum at the #1 throttle body supply port during any conditions.

Who knows? I have never been a supporter of disabling any part. My vehicle is now running well with the vacuum switch in operation.

    

7Back to top Go down   Early 85 K100 Vacuum Switch Empty Re: Early 85 K100 Vacuum Switch on Thu Nov 29, 2012 9:16 pm

RicK G

RicK G
VIP
VIP
To the best of my knollege there is nothing detrimental about the switch so why stuff with it if it's working without any problems.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

8Back to top Go down   Early 85 K100 Vacuum Switch Empty agreed on Thu Nov 29, 2012 10:10 pm

ibjman

ibjman
Life time member
Life time member
Could it be, that there may be something actually beneficial about keeping it (even if it may not be readily apparent)?

A lot of folks say that because they don't SEE any effect of whatever subtle timing adjustment it creates that there is none.

Also, when BMW discontinued it's use I think it's higly likely that they made some other adjustments to the fuel/timing overall management to offset the removal of the switches function.

My best guess is that it could have been intended to retard the timing a few degrees (anti-knock) during periods of very high throttle load at lower rpm ranges????? I guess I need to connect a vacuum gauge with a TEE connector to throttle body #1, hang it on the tank and go for a ride to see if I can create a situation where the vacuum actually drops below .06 bar while running.

    

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