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Thread: TPS Alignment, Idle Speed Adjustment: Beyond Zero=Zero

  1. #16
    Registered User roger 04 rt's Avatar
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    Oct 2011
    Florida & Massachusetts
    i received a PM which asks the question, where does the 250 mV at 0 (zero) degrees come from. I mentioned it at the start of the thread but the answer is that 250 mV comes from the Bosch TPS data sheet below.

    The TPS is specified as a voltage divider Ua/Uv, where Ua is the output voltage going to the Motronic and Uv is the input voltage coming from the Motronic. You can measure Uv on pin 2 of the TPS, it is 5V. At zero degrees rotation, the TPS spec shows a voltage divider ratio of 0.05, which calculates to a voltage output of 250 mV.

    It's not surprising that Bosch designed the TPS this way. Since good accuracy is critical at small throttle angles, it is appropriate to move the wiper of the potentiometer off its end of travel.

    The diagram below also shows that the first potentiometer in the TPS reaches the end of its range at 23 degrees. It is conjecture on my part but I believe that the reason for rotating the throttle twice after a Motronic reset is to allow the Motronic to use the more accurate fine wiper to measure the starting point of the less accurate coarse wiper. It may also be useful in measuring the end of travel for determining WOT.


  2. #17
    Registered User roger 04 rt's Avatar
    Join Date
    Oct 2011
    Florida & Massachusetts
    May 2017: Outline for Zero=250 mV added.

    Although most everyone in this forum has a good procedure for synchronizing their R1150's throttle bodies, I recently reviewed the full BMW Repair Manual procedure, used it recently, and found it excellent for achieving good balance and proper cable tension.

    The main problem with the BMW procedure is that it’s written for someone with a BMW test station. Below is the procedure, directly from the manual but with edits for clarity and to replace BMW specific and outdated terminology. There are also some Ed. Notes that I’ve added with practical clarifications.

    BMW R1150RT Repair Manual
    Procedure 13 60 110
    Checking throttle-cable play, checking and adjusting idle speed and throttle-valve synchronization

    - Notes and Attention (in red) from BMW Repair Manual
    - Ed. Notes and other edits by me for clarity--e.g. Choke changed to Fast Idle Lever, Carburetor changed to Throttle Body
    - Headings (e.g. STEP 1, …) added by me for clarity

    STEP 1: Preparation
    - Test-drive the motorcycle until the engine is warm.
    - Remove the left side panel.
    - Remove the right side panel.
    (Ed. Note: BMW Manual indicates remove small access panel in fairing but mine is glued in)

    Oil temperature: least 90 C (194 F)

    Ed. Note: Adjuster is at the Handlebars
    - Push back rubber caps on throttle and fast-idle cables.
    - Use the adjusting screws to increase the play of throttle and fast-idle cables.
    (Ed. Note: Two turns will create about 1 mm.)

    Fast Idle cable free travel: ........................................approx. 1 mm (0.0393 in)
    Throttle cable free travel: ........................................approx. 1 mm (0.0393 in)

    Ed. Note: Adjuster are at the Throttle Bodies
    - Turn the adjusting screws to increase the play of the cables for the left and right throttle valves.
    Throttle valve cable free travel: ....................................... approx. 2 mm (0.0787 in)
    (Ed. Note: Two turns of the TB adjuster is about 2 mm.)

    Ed. Note: STEP 1.5: Zero=250 mV Procedure
    -Resetting the throttle stop screws is specifically cautioned against by the BMW procedure.
    -Procedure might be useful if someone has already tampered with TB stop-screw adjustment.
    -This should be considered a last resort to solve other TB sync problems.

    Simplified Zero=250 mV Procedure
    --Loosen all throttle and fast idle cables
    --TBs and BBSs must be clean
    --Set TB BBSs to 2.5 turns (just a starting point) and make them equal.
    --Center and fully close both TB butterfly valves
    --Set TPS to 250 mV and lock TPS screws (no further adjustment of TPS required)
    --Open left TB and count stop screw turns after contact until TPS reads 340 mV. Lock left stop screw (no further adjustment).
    --Set right TB stop screw open same number turns as left.

    --Start engine, warm up to at least 3 bars.
    --Balance at idle using only right TB stop screw, do not touch BBS. RPM does not matter
    --Lock right TB stop screw.

    --Follow remainder of this procedure

    STEP 2: Adjust Idle Speed and Left/Right Idle Syncronization
    - Connect hoses of your throttle-body vacuum-synchronization tool (e.g. Twin Max, Harmonizer) to the vacuum ports on the left and right throttle bodies.
    - Start the engine.

    ! Attention: Do not allow the engine to idle for longer than is necessary, because the trim panels near the exhaust could be damaged.
    (Ed. Note: Use a fan to move air past cylinder heads and oil cooler.)

    - Adjust idle speed by turning the air bypass screws while checking that the throttle bodies are balanced.
    Idle speed: ........................................ 1,100 ±50 rpm
    (Ed. Note: A hot idle speed above 1100 rpm, results in leaner AFR readings during cold-starting, this based on data from GS-911 logs from several R1150R/GS/RTs.

    Note: Make sure that both throttle valves are closed.
    (Ed. Note: firmly resting on the throttle stop screws)

    ! Attention: Do not tamper with the sealed stop screws of the throttle valves, as otherwise the idle-speed volume flow will have to be reset by the manufacturer.

    STEP 3: Remove Free Play from Throttle Body Cables
    - Carefully turn the adjusting screw of the left throttle valve and reduce play until the reading of the vacuum synchronization tool changes.
    - Turn the adjusting screw very slightly in the opposite direction until the reading returns to its original value.
    - Tighten the locknut to secure.

    Note: Make sure that the reading does not change when you tighten the locknut. Adjust throttle cable play at throttle valve so that no play is perceptible, but the throttle valve reliably contacts the stop screw (no strain on cable).

    - Adjust the right throttle valve in the same way.

    Note: Zero play can cause the throttle valves to rattle.
    (Ed. Notes:
    -One quarter to one half turn of the TB adjuster results in 0.25 to 0.5 mm slack.
    -Considering this warning, and the instructions above to "adjust so that no play is perceptible" if the throttle cable adjusters on the throttle bodies require adjustment later in Step 5, either the left or right (as appropriate) should be turned clockwise, so as to not remove the "imperceptible play”.
    -The BMW procedure says to use engine rpm or engine vacuum-balance to indicate when the throttle cables are fully tensioned and have started to move. A much more sensitive indication can be had by monitoring the TPS voltage between pins 1 & 4. When the voltage starts to increase, the throttle is moving. This will work for the left TB, Fast Idle Lever and Throttle Twistgrip. Because the adjuster for the right TB doesn't move the TPS, it won't work for that adjustment.)

    STEP 4: Adjust Throttle and Fast Idle Lever Free Play
    - At the right handlebar, use the adjusting screw to adjust play of the throttle cable.
    Play of throttle cable: .....................................approx. 0.5 mm (0.0197 in)
    (Ed. Note: One turn of the adjuster is about 0.5 mm.)
    -Push the rubber cap into position over the adjusting screw.
    (Ed. Note: Remember to secure the locknut.)

    - At the left handlebar, use the adjusting screw to adjust play of the fast-idle cable to zero.
    - Push the rubber cap into position over the adjusting screw.
    (Ed. Notes:
    -Remember to secure the locknut.
    -Some fast idle cables have stretched to the point that zero play cannot be achieved. A spacer can be fabricated and added between the end of the cable and bottom of the adjuster ferrule.
    -This results in the throttle-valves being opened about 4 degrees and results in a TPS voltage of about 1000 mV in the mid-detent position. Based on many R1150 GS-911 logs, most Fast Idle Levers are not adjusted this tightly. It is quite common to see as little as 0.96-1.28 degrees of throttle advance with the Fast Idle Lever set, which may explain many cold-starting problems.
    -You may find that the mid-detent idle speed it too high with no slack. If so, add slack to suit your preference.)

    - Move the handlebars all the way from left to right and check the settings. Make sure that engine speed does not vary when the handlebars are moved in this way.

    STEP 5: Check and Adjust Left/Right Synchronization at Off-Idle Throttle Positions
    - Repeatedly open the throttle gradually and increase engine speed from idle to approximately 2,500 rpm to check throttle-valve synchronization. (Readings shown by synchronization tool must increase and decrease together). If necessary, correct by turning the adjusting screws of the throttle-valve cables at the throttle body.
    (Ed. Notes:
    -As mentioned above, either the left or right adjuster should only be turned clockwise, otherwise the adjuster will be over tensioned and play will be reduced to zero.
    -Determine which adjuster to turn clockwise as follows: if the vacuum-balance tool shows more vacuum toward the left throttle body, turn the right TB adjuster clockwise. Likewise, if the vacuum-balance is toward the right TB, turn the left TB adjuster clockwise.
    -When you tighten the locknut, the TB cable will be tensioned a slight bit more, anticipate this by slightly under-adjusting the tension.)

    Note: Make sure that when the throttle grip is released both throttle valves return to their fully closed positions.

    STEP 6: Completion
    - Tighten the locknuts and recheck throttle body balance.
    - Seal off the vacuum bores or reconnect charcoal canister purge hoses.
    - Reinstall Left/Right Fairings, assembly is the reverse of the disassembly procedure.
    (Ed. Note: I love that BMW phrase, “assembly is the reverse of the disassembly procedure.”)

  3. #18
    Registered User Blacque Jacque Shellacque's Avatar
    Join Date
    Nov 2005
    Pickering, Ontario
    Thanks Roger, awesome write up.

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