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Point-Seven-five


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The ignition switch is a good thing to check.  I had much trouble with mine last year on a bike that had always been garaged and was in otherwise pristine condition. 

I suspect that the problem is due to a design that puts very little contact force on the internal electrical contacts, making them somewhat sensitive to the slightest bit of dirt or corrosion. 

I suspect the reason you see it more at low rpm's is that the vibration of the engine is less as the rpm's increase, shaking the switch internals less.  As the problem progresses you will have the pleasure of having the electrical system shut down momentarily, usually on the highway at speed, which is what finally convinced me to go in and clean the switch.

    

Holister

Holister
Life time member
Life time member
@Point-Seven-Five wrote:As the problem progresses you will have the pleasure of having the electrical system shut down momentarily, usually on the highway at speed
.... and its even more pleasurable when that happens at night time. affraid Throw in a corner and you'll be having a real hoot.

Don't delay. Its a common problem and well documented here on the forum.


__________________________________________________

1989 K100RT     VIN  0097367 (naked)  
1996 K1100RS   VIN  0451808
  Fast Idle .... Latest: It is finally fixed! - Page 2 Austra12    Fuel:  95 Octane
Engine Oil: Nulon Full Synthetic 15W50
Gear Box Oil:  Nulon Synthetic 75W90
    

Kafflut

Kafflut
Silver member
Silver member
@charlie99 wrote:
the afm is where it all happens ...you could perhaps open it up and go 1 click looser on the springing

whilst doing that measure the resistance of the wiper at closed throttle
or even better ...apply voltage to the system and read what voltage you are getting at closed afm

I found that a voltage of about 1.65 volts is about right for a static closed throttle from the afm .
the pc board that hold the resistance part of the mechanism can be moved slightly on its board mounts ...which can make a fair bit of difference

likewise the arm that sweeps the laser cut resistor board can be manipulated to read a different value on closed afm

there is a bolt arrangement that holds it all in place on an armature attached to the vane inside the afm ........




Hello again Charlie

I revisited this post of yours and decided to check out my AFM. I followed the instructions in the TroubleShooting document by Bertrand Vogel (Crazy Frog), link at the portal. Apply 12 volts between pins 5 & 8 and measure the voltage between 5 & 7 for different vane positions. At closed I measured about 1.8volt.

Please will you comment on my results:

Fast Idle .... Latest: It is finally fixed! - Page 2 Afmtes10




I should clarify the vane position numbers. I used the depth rod of a vernier to push the vane, open it in 2.5mm increments, resting the shoulder of the main scale against the vane stopper block. It's not ideal, but it's an indication. The closed position of the vane corresponds to 15mm on my vernier.

Please refer back to the suggestions you made in the original post. Do my measurements indicate I should do some of those things? Do you think I should open it up and "go one click looser on the spring"? Would that help in lowering my idle revs, still a smidgen high for my liking?

I read instructions elsewhere on the forum how to reposition the mechanism so a fresh surface of the contact surface is used - does anybody know where I can find that information?

http://bmwk100k75.weebly.com/
    

charlie99

charlie99
VIP
VIP
that curve looks pretty good to me (although there is a slight dip at the end , but well out of the working range expected )
and about the right starting volt measurement

I wouldn't be going in there at all.... yet !

I would suggest there are other things that need to be sorted before even thinking about it .

just a  question , did you notice if there was any movement of the barn door up or down , along the axis of the pivot pin ..?

I have seen slight lateral movement of this , just a tiny bit but it did not affect the wiper readings ...just wondering

btw  did you also measure the temperature sensor on the afm ?  forgotten the pin numbers at this moment
its just a test to prove that it is in circuit and works ...(they are quite sensitive , just blowing across it can produce good swing results )

good luck


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OFast Idle .... Latest: It is finally fixed! - Page 2 Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

Kafflut

Kafflut
Silver member
Silver member
Thanks for the feedback, Charlie

I did not notice lateral movement on the vane.

Engine Temperature Sensor

I took two readings (Pin 10), 0.9K after running the engine for a while and 2.6K after leaving it overnight.

Referring to page 18 on that wonderful TroubleShooting document, the .9K suggests about 50 degrees C and the 2.6K about 20 degrees.

The 20 degrees indicated by the 2.6K looks right. I measured the room temperature at that time and it was just short of 20 degrees.

I could not verify the 50 degrees. It looks a bit on the low side; I'd expect the engine to be warmer than that - could it be if the EFI thinks the engine is less warm than what it actually is, actual temperature say 65 and the sensor indicates 50, it would send more fuel, consequently faster idle?

Resistance measurements (AFM)


The Typical Values are from, again, that TroubleShoot document, page 25
My values, the measured values on my bike, seem okay except the 76 ohm value is a smidgen lower.


Fast Idle .... Latest: It is finally fixed! - Page 2 Afmtes11



Does this information in anyway change the feedback you have given me up to now.

Have a super weekend

http://bmwk100k75.weebly.com/
    

charlie99

charlie99
VIP
VIP
don't worry about it ...the temp sensor is deep in the airflow path ..which runs considerably cooler than the ambient temp of the hardware surrounding it given that air is flowing (and cooling )


the temp sensor in the afm is operating as a compensation circuit to make minor adjustments to the readings of the afm back to the efi computer ...considering the temperatures experienced by the air flow temperature ..its a feedback circuit 
so far the system seems to be showing all the standard expectations

keep at it  and of course... good luck !


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OFast Idle .... Latest: It is finally fixed! - Page 2 Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Just to expand slightly on Charlie's excellent information.  The temperature probe in the air path is giving the ECU information that it uses to determine the density of the air.  Cooler is more dense than hot and thus needs(or can handle) more fuel.  This is how the MAF sensor is able to accurately tell the ECU how much oxygen is coming into the engine for combustion. 

As the AIR temperature INCREASES, the ECU will inject LESS fuel for a given flap position. 

This has nothing to do with engine temperature.  The mixture adjustment for engine temperature is done via the water temperature taken by the sensor in the radiator line at the top front of the engine block.  The enriching controlled by this sensor is the reason why the engine doesn't need a conventional choke.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

58Back to top Go down   Fast Idle .... Latest: It is finally fixed! - Page 2 Empty More Observations on idle revs Sun Dec 18, 2016 3:14 am

Kafflut

Kafflut
Silver member
Silver member
Shocked
The AFM vane, the little "barn door", oscillates while the engine is running - is this right? From what I've seen in photos of the inside of the AFM, I'd think that sweep arm will wear a hole in the contact surface. I'd say it moves +/- 3 mm from the average position, say a swing of about 5 mm.

At idle the oscillation frequency is probably lower. My guess is at high revs it would perhaps not happen.

How did I find this out? I removed the air filter and the lower part of the air filter box-AFM still connected to the air delivery. Then I stuck my finger into the AFM opening - don't ask what I thought I'd discover.

Besides the oscillation I made a further discovery: If I disconnected the AFM from the plenum and activated the vane with my finger I could position the vane so the engine revs remain at 1000, not the above 1250 it does with the AFM connected. The engine now sucks as much air as the closed butterfly valves permit - I'm guessing - but the amount of fuel injected is determined by the manually operated deflection of the vane.

NOTE: Throttle cable is disconnected. Fast idle is disconnected. TPS is removed - can't obstruct movement. I checked, the hose clamps do not touch the mechanism anywhere.

Based on the above, my conclusion(or maybe confusion is a better word) regarding the fast idle is:
Is it caused by the engine sucking too hard?
Maybe the butterfly valves don't close completely?
Or maybe the butterfly valves are shut as far as they can go, but are worn and no longer restrict air flow sufficiently to permit a decent idle speed?
Or all the above?

Who can throw light on this?

My conclusion about the vibrating/oscillation of the vane is:

Surely the volume of air in the plenum chamber should act as damper and prevent the oscillation?

Can anybody throw light on that?



Last edited by Kafflut on Sun Dec 18, 2016 5:58 am; edited 1 time in total

http://bmwk100k75.weebly.com/
    

AL-58

AL-58
Life time member
Life time member
Have you tried disconnecting the throttle cable to see if its just the cable holding the TBs open slightly?

My RT had a (new) cable where the cable outer was a litle too long holding the throttles open.  Some very careful trimming back fixed it.

Al


__________________________________________________
'87 K100RS/HRD sidecar (1100 motor)  sc25 

'87 K100RT with Paralever backend

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

Fast Idle .... Latest: It is finally fixed! - Page 2 K-dogs10
    

walfish

walfish
Life time member
Life time member
"Maybe the butterfly valves don't close completely?"


This may be due to an incorrectly fitted TPS,suggest you remove the TPS from it's position on the shaft until you're satisfied with the idle speed then refit it.
Don't ask how I know.


Ex- Durbanite .(kannieklaarnie)
Fast Idle .... Latest: It is finally fixed! - Page 2 22936


__________________________________________________
Fast Idle .... Latest: It is finally fixed! - Page 2 Uk-log10 88 K 100  0033026 
   
                            92 K 1100 LT  6455097
    

Kafflut

Kafflut
Silver member
Silver member
I have modified the original post. I should have said in there that the obvious stuff I've taken care of as much as I know how - I added this note to the post:

NOTE: Throttle cable is disconnected. Fast idle is disconnected. TPS is removed - can't obstruct movement. I checked, the hose clamps do not touch the mechanism anywhere.

http://bmwk100k75.weebly.com/
    

walfish

walfish
Life time member
Life time member
The post is a little long, so I probably missed some points.

Your only option now is to balance the Throttle Bodies to achieve a lower idle speed.

Fast Idle .... Latest: It is finally fixed! - Page 2 22936


__________________________________________________
Fast Idle .... Latest: It is finally fixed! - Page 2 Uk-log10 88 K 100  0033026 
   
                            92 K 1100 LT  6455097
    

RicK G

RicK G
admin
admin
The flap should not move when at idle. There is a bypass around the flap so as to supply air at idle.
Open the bypass at the MAF up quite a few turns then balance the throttle bodies using the big brass screws (approx 11/2 turns out from stop) with the butterflys closed completely then when the idle is even with the same readings on each cylinder start closing the air bypass on the MAF until it falters then back about 1/4 turn. That way the flap should start to open as soon as the throttle is opened providing all the butterflys are evenly set.


__________________________________________________
"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 2004 K1200GT 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki
    

Kafflut

Kafflut
Silver member
Silver member
@RicK G wrote:The flap should not move when at idle. There is a bypass around the flap so as to supply air at idle.
Open the bypass at the MAF up quite a few turns then balance the throttle bodies using the big brass screws (approx 11/2 turns out from stop) with the butterflys closed completely then when the idle is even with the same readings on each cylinder start closing the air bypass on the MAF until it falters then back about 1/4 turn. That way the flap should start to open as soon as the throttle is opened providing all the butterflys are evenly set.

Rick that sounds like a real possibility. It may be that the bypass passage on my AFM is blocked. What you say makes a lot of sense

Scenario: bypass is blocked or somewhat blocked - the vane will tend to open - more fuel because the EFI gets a "vane open" signal - even with closed butterflies the motor will tend to rev higher

I'll be taking out the AFM and see if that passage is clear

http://bmwk100k75.weebly.com/
    

Kafflut

Kafflut
Silver member
Silver member
Rick


Where is that bypass air passage?

I took out the AFM bypass adjuster screw and I can't see what's at the bottom of the hole.

Here's my thinking; bypass air must be pulled from a) upstream of the vane or b) from outside of the body of the AFM, right? I cannot see any opening that would let in "unmeasured" air.

I did a very crude test as well; I rigged up the AFM, a resistance meter and Hoover nozzle on the bench. I measure resistance between pin 7 & 5, 0.076K with the vane in closed position. Then with the bypass screw seated(closed) I moved the Hoover nozzle to where the meter registered a small increase( i.e. the vane just starting to open), 0.085K, a bit erratic, but a very low increase. Then I gradually opened the bypass screw many turns. No change in resistance.

I don't consider this conclusive, like I said it is very crude.

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66Back to top Go down   Fast Idle .... Latest: It is finally fixed! - Page 2 Empty Fast Idle Fixed Thu Dec 29, 2016 9:04 am

Kafflut

Kafflut
Silver member
Silver member
I was reluctant to claim "fixed" before I'd been for a test run. I went for a 15 minute ride. The motor was nice and hot and it idled on the 1000 rpm mark. Those who have been plagued with warm engine idle revs around 1500 to 1700 rpm and that you just can't adjust down will understand my joy Very Happy

Thank you to all who offered suggestions and ideas.

It has been a long search. From the start I suspected the throttle valves were not shutting properly. With throttle & fast idle cables removed, idle switch aka throttle position switch removed, no physical interference from those TB hose clamps and the stop screw not touching the stopper, idle revs would go higher as the motor warmed up towards that very noisy 1700 level.

I removed the TB assembly and, on the bench, adjusted those never-to-be-touched inter-TB adjusters. I will post a separate thread on how I did that. It may be that one of the throttle valves was bottoming out and preventing the others from closing or maybe just wear - it's an old bike.

Knowing what the problem is, is important, but equally so, in my opinion is knowing what didn't cause the fast idle.

You will be familiar with the drawing from Bert's document below.  Except for the motor and the Hall sensors I swapped out every component shown in that drawing - I have another K100. I also tested the AFM, the coolant temperature sensor and air temperature sensor. I replaced all rubbers between the TBs and the AFM. The breather pipe was broken; replacing that helped some, but the rest made no difference to the fast idle.
Fast Idle .... Latest: It is finally fixed! - Page 2 Efi__e12

So that's the short part of the story. I'll do another thread later on how I did butterfly valve adjustment. I will also post stuff I discovered about my AFM

Thanks again for your advice and ideas.

http://bmwk100k75.weebly.com/
    

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