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#999142 - 10/17/17 12:19 PM Possible way to adjust messed up TB stop screws  
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14TLC Offline
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Hello everyone. This is my first post on this forum and I want to share some findings for adjusting throttle body stop screws on camhead. This is work in progress so I'm not 100% positive whether it will work for everyone. I have done it on one bike only, so not enough statistics.

I strongly oppose to even touch the stop screws, even on older models (referring to zero to zero procedure). Yes you can do it, but you can mess other things in ECU fueling maps. Not to mention that by this process you are artificially correcting something and by doing that you can mask some other issues with the bike.

I worked on my friends R1200GS ADV Camhead 2010. He both it as used bike with little to none service history. After difficulties with TB sync I have noticed that someone has been playing with the stop screws and the differential vacuum at idle was outside of specified 25mbar values. Of course the reason for this can be something else, but after checking everything else I dared to adjust the stop screws. So here it goes:

Preconditions: Fully functional and clean throttle bodies, injectors, idle stepper motors, TPS, oxygen probes, exhaust flap, fuel pump, fuel pump controller, fuel pressure regulator, fuel hoses etc. Correctly adjusted valves, clean air filter, no air leaks, no blockage in air paths

Tools needed: Precise TB sync tool which can measure small differential vacuum. Diagnostic tool like GS-911 or some other BMW diagnostic tool.

The theory in mind was to adjust the stop screws without moving the TPS. Target was to adjust them so the differential vacuum is within spec and at the same time O2 sensors reading Lambda = 1

Step by step procedure:

1. Reset adaptation values and without touching the throttle let the bike idle until reaching operating temperature. Four bars on temp gauge or minimum 60 degrees Celsius. Switch off the ignition and wait for about 5 minutes

2. Switch on ignition and calibrate exhaust flap and idle stepper motors then switch off ignition

3. TPS reset

- with ignition off, open the throttle twist grip to wide open position and while holding it there turn on ignition and wait 15 seconds

- while still holding the throttle open, turn off ignition and wait for another 15 seconds before letting go the throttle

- turn on ignition and wait for another 15 seconds then turn off ignition

4. Fixing TPS in position. With the ignition off disconnect the connector from the TPS. Measure the resistance between middle and right pin on the TPS and write down the value. Remove the TPS from the throttle body and fix the TPS to the same value measured before. This can be tricky since the TPS is very sensitive and very easy to move. I used play dough to do this :-). Connect the TPS connector and just let the TPS to hang.

5. Slacken the throttle cables on both TB and let a lot off play so they can not interfere with stop screws adjustment

6. Loosen the stop screws and turn the fixing nut far from the butterfly point so you have enough thread for adjusting

7. Connect the TB sync tool as usual

8. Connect the diagnostic tool and start the bike. Monitor the engine temperature and O2 sensor values. After reaching engine temperature over 60 degrees Celsius, start adjusting the stop screws side to side until reaching near Lambda = 1 on both O2 sensors. At the same time follow the TB sync tool to confirm that both TBs are in sync and within specified 25 mbar differential vacuum with left cylinder leading slightly. This is very tricky because there is limited access to the stop screws and you don't want to overheat the engine. Best to have some cooling fans. The most tricky part is fixing the stop screws. Even slight movement can make difference.

9. After fixing the stop screws, turn ignition off and screw the TPS back on the TB.

10. Do a TPS reset as described in step 3.

10. Adjust the TB cables and go through regular TB sync procedure.

As I wrote earlier this is work in progress. While I was adjusting the stop screws I was also following the idle stepper motor openings. What is not clear to me is what would be the target for Lambda factor on O2 probes and idle stepper openings. I did not have any previous data from working bike to compare. Before I started the stop screws adjustment, Lambda factor was 0.85 which is rich mixture and I could smell that from the exhaust so decided to reach Lambda = 1. Ended with Lambda = 1 and idle stepper motor opening of 20% at operating temperature.

Maybe someone have also worked on this issue and we can compare some data for Lambda parameters and idle stepper motors on issue free bike. Maybe roger 04 rt can help here with his findings and experience.

#999147 - 10/17/17 01:25 PM Re: Possible way to adjust messed up TB stop screws [Re: 14TLC]  
Joined: Jun 2010
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dirtrider Offline
The Oracle
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Morning 14TLC

I guess I'm really missing something here or you left some things out of your procedure?

Using lambda to set idle screws seems fruitless as the lambda is self correcting by the fueling computer so you are sort of chasing a ghost.

I see no mention of holding the idle steppers at a fixed value during the screw adjustment so you (we) have no idea on how much of your base screw setting is being cancelled out or added to by the computer controlled stepper pintle position.

What WAS the original stepper count (position) before messing with the base idle screws? What is the present hot engine idle stepper counts (position) after a nice long ride then drop to curb idle. What is the cross side stepper count delta at hot engine idle? What WAS the stepper count delta at hot engine idle with the >25mbar reading?

Are BOTH side throttle cams now lifting off their base idle stop screws at EXACTLY the same time as the twist grip is turned? (this is a very important observation)

Your TPS re-learn procedure seems strange, I haven't seen that in any of the BMW 1200 manuals that I have? (on the BMW 1200 bikes that do use a TPS re-learn it has always been a key-on full throttle sweep from closed to full open)

Last edited by dirtrider; 10/17/17 01:30 PM.

D.R. ___
Sent from my rotory dial wall phone!
#999176 - 10/17/17 11:52 PM Re: Possible way to adjust messed up TB stop screws [Re: 14TLC]  
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14TLC Offline
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Hello dirtrider,

Everything that you have pointed out actually crossed my mind in different stages of the process. I was also surprised about the lambda factor behavior. I will explain what was actually happening so you have better picture. This was my first time doing this so I maybe I left out some essential steps in the process. Wanted to share this so I can hear opinions and experiences.

The bike had very erratic idle and often stalls. First thing was faulty TPS at near idle position. Almost every time after releasing the throttle it will land with different values. There was improvement after changing the TPS, but the engine was off balance. During the TB sync I have noticed that the throttle stop screws were messed. Broken paint marks and obvious scratch from screwdriver.

The diagnostics that a was using did not have data logging and graphing of live data for further analasis. It also not have feature to manually lock the idle stepper motors and at the same time watching other parameters like temp, idle steppers position. injection period and lambda factor. It was quite difficult to track changes in values just looking the numbers while the engine had erratic idle and stalls. So I installed some desktop screen recording software to record the changes which unfortunately ended with corrupted video file. If I remember correctly the right cylinder was pulling more vacuum and had about 0.1 lambda factor grater then the left cylinder. Maybe 0.92 over 0.82, but not sure. I don't remember the position of stepper motors.

Because I could not lock the steppers I started adjusting the stop screw like described in previous post with stepper motors on. What was interesting is that lambda factor fluctuates around present value with +/- 0.05. I turned the right stop screw to match the lambda of the left cylinder and stabilize the erratic idle behavior. From that point on I started adjusting both stop screws little by little. When turning the screws, lambda factor was in fact changing and it will stay in position when not turning the screws. There was little +/- fluctuation as temperature raised, but not significant change as that when turning the stop screws All this with TPS removed from the TB and fixed in position. While lambda factor was rising the stepper position was dropping in % to compensate. The representation of stepper position was in %. Starting from 100% with engine not running, about 85% after cold start and it will drop as the engine temperature rises. After the adjustment I ended with Lambda factor fluctuating around 1 on both cylinders and steppers with position around 20% on both cylinders. While doing this I was also watching the TB sync tool which ended with around 6 to 8 mbar differential vacuum.

I don't really know if these values are the target. I'm also a little bit skeptic, especially for the stepper position which I think with 20% left , much of the adaptation range has been used. That is why I'm asking if someone have these values from another bike. Positions of the steppers, lambda, injection period related to the engine temperature.

Related to the butterfly valves, I'm pretty sure they start raising at the same time. This is controlled by the cables after proper cable adjustment if you referring to that.

Do you have any experience in adjusting stop screws on camhead or hexahead models with stepper motors. I have not come across any solution posted on internet.

Referring to the TPS reset, I have seen that procedure at a dealer after software upgrade of one R1200GS camhead. There was no specific command to start this procedure but the diagnostic software itself instructed this. I think it was called something like manual stepper calibration, but the technician said that it was TPS teaching procedure. There was no instruction how much time to wait but the software itself was telling when to hold and release the throttle and when to switch on/off ignition, but time intervals were 10-15 seconds. Also here http://www.rexxer.com/fckimages/BMW-TPS-Reset-PDF.pdf

Last edited by 14TLC; 10/18/17 12:00 AM.
#999202 - 10/18/17 12:43 PM Re: Possible way to adjust messed up TB stop screws [Re: 14TLC]  
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David R Offline
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It seems you could turn the key off, then to on allowing the steppers to reset then unplug them. They should be even at every key on.

Then adjust the vacuum to match both sides ignoring everything else.

This is after making sure valve adjustment in in spec.

Correct me if I am wrong.

David


'76 R75/6 67,000 miles
2000 R1100RT 137,000 miles. (retired)
11 Versys 11,000 miles
12 R1200R!
#999203 - 10/18/17 01:11 PM Re: Possible way to adjust messed up TB stop screws [Re: David R]  
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14TLC Offline
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Originally Posted by David R
It seems you could turn the key off, then to on allowing the steppers to reset then unplug them. They should be even at every key on.

Then adjust the vacuum to match both sides ignoring everything else.

This is after making sure valve adjustment in in spec.

Correct me if I am wrong.

David

If it was so simple :-) When steppers are disconnected, the BMSK will run with predetermined fueling map and making the adjustment useless when connected again. You can adjust matching vacuum at any TB butterfly position. But which is the correct one that will allow specified air volume with range for steppers for correction.

Disconnected and parked steppers are different things altogether.

#999204 - 10/18/17 01:13 PM Re: Possible way to adjust messed up TB stop screws [Re: David R]  
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dirtrider Offline
The Oracle
dirtrider  Offline
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Originally Posted by David R
It seems you could turn the key off, then to on allowing the steppers to reset then unplug them. They should be even at every key on.

Then adjust the vacuum to match both sides ignoring everything else.

This is after making sure valve adjustment in in spec.

Correct me if I am wrong.



Morning David

You have the basic idea but it won't work that easy. Depending on engine temp the steppers won't do a key-on reset to curb idle counts but will reset to engine starting counts which are well above the basic hot engine curb idle counts.

If a person could fool around with the idle RPM & get each stepper to settle in at the required hot engine idle count, THEN, disconnect each stepper at that exact count then your method should work. (or at least be a good basis for a baseline to start from then match the actual running counts vs curb idle vacuum delta vs throttle plate initial lift point


D.R. ___
Sent from my rotory dial wall phone!
#999206 - 10/18/17 01:21 PM Re: Possible way to adjust messed up TB stop screws [Re: 14TLC]  
Joined: Jun 2010
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dirtrider Offline
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dirtrider  Offline
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Originally Posted by David

If it was so simple :-) When steppers are disconnected, the BMSK will run with predetermined fueling map and making the adjustment useless when connected again. You can adjust matching vacuum at any TB butterfly position. But which is the correct one that will allow specified air volume with range for steppers for correction.

Disconnected and parked steppers are different things altogether.


Morning David

I don't believe this to be true--- On the BMW 1200 the steppers are 4 wire steppers so there is NO direct feedback of stepper position or operation to the BMS-K. Therefore it should still run in closed loop with dynamic fueling correction even with the steppers disconnected.


D.R. ___
Sent from my rotory dial wall phone!
#999207 - 10/18/17 01:23 PM Re: Possible way to adjust messed up TB stop screws [Re: 14TLC]  
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14TLC Offline
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@ dirtrider

Do you know what is the count range of the steppers as per GS-911 so I can relate with percentage readings that I have.

#999209 - 10/18/17 01:35 PM Re: Possible way to adjust messed up TB stop screws [Re: 14TLC]  
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dirtrider Offline
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Originally Posted by 14TLC
@ dirtrider

Do you know what is the count range of the steppers as per GS-911 so I can relate with percentage readings that I have.


Morning 14TLC

Lots of variables on this one as it depends on engine oil viscosity, altitude, air density, alternator loading, alcohol content in the fuel, transmission gear oil thickness (if running in neutral with clutch engaged), miles on engine, engine compression, etc.

I do have some trapped 1200 camhead idle count data (possibly with altitude numbers) but I am not near that data at the moment as it is on my shop computer.


D.R. ___
Sent from my rotory dial wall phone!
#999210 - 10/18/17 01:43 PM Re: Possible way to adjust messed up TB stop screws [Re: dirtrider]  
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14TLC Offline
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14TLC  Offline
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Originally Posted by dirtrider
Originally Posted by 14TLC
@ dirtrider

Do you know what is the count range of the steppers as per GS-911 so I can relate with percentage readings that I have.


Morning 14TLC

Lots of variables on this one as it depends on engine oil viscosity, altitude, air density, alternator loading, alcohol content in the fuel, transmission gear oil thickness (if running in neutral with clutch engaged), miles on engine, engine compression, etc.

I do have some trapped 1200 camhead idle count data (possibly with altitude numbers) but I am not near that data at the moment as it is on my shop computer.






Thanks. This would help for better understanding.
I was also referring to the complete range as steps end to end positions. To make relation for example 100 counts in GS-911 to percentage in my readings.

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