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Thread: M70 DK throttle valve cleaning DIY with test data

  1. #1
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    M70 DK throttle valve cleaning DIY with test data

    http://twrite.org/shogunnew/fixes/throttle.html

    another write-up sent to me by by George Fontes, see refurbish DK motors

    and here I added in English and German language
    DK input details : small PDF file

    click here>>
    http://twrite.org/shogunnew/data/controlsystems.html
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  2. #2
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    I went through all this on a 1989 E32-750iL Highline because it has such a shitty idle even though I had the intake manifold gaskets done and all other potential false air intakes removed.
    So I finally decided to check the vacuum on both sides and found a massive difference. About 500mBar one side vs. 700mBar on the other side.
    Running out of ideas I swapped the DKs from left to right and vice versa and the vacuum switched as well. So it is clear that it is not an engine air leak but the DKs themselves.
    To cut a long story short:
    I found that the throttle butterflies leave a more or less large gap in fully closed position and the synchronization is obviously not able to take care of this. I ran the specific procedure plus drove the car for almost 200km and still the same. I put in another set of used DK motors and the vacuum difference is less but still there and also here I found one DK unit with a rather large gap while the other one appears to be 100% shut. To me it seems the butterflys themselves wear and I'm now having a set of DKs re bored and a new set of butterflys made. I hope this will cure my problem.
    Has anyone made similar experiences?

  3. #3
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    I was thinking about refubishing mine butI have a slight problem.

    My DK's are not put together with torx or phillips screws, but this strange tamper proof type I have not seen before, and I do not have a tool to open them.
    I was searching the internet but could not find a picture.
    -Egil (my name)

    2012 ///M550xd touring
    1990 850Ia Hartge Supercharged.
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  4. #4
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    Quote Originally Posted by Noggie View Post
    I was thinking about refubishing mine butI have a slight problem.

    My DK's are not put together with torx or phillips screws, but this strange tamper proof type I have not seen before, and I do not have a tool to open them.
    I was searching the internet but could not find a picture.
    Egil, itīs a one-way-screw to be opened with a (good) pipe wrench.
    Then replace it with stainless steel torx screws.
    Last edited by 8Harry8; 03-27-2010 at 02:11 AM.
    to register your 8 @ www.8coupe.com!

    Best regards from good old Germany Harry!

  5. #5
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    Quote Originally Posted by Noggie View Post
    I was thinking about refubishing mine butI have a slight problem.

    My DK's are not put together with torx or phillips screws, but this strange tamper proof type I have not seen before, and I do not have a tool to open them.
    I was searching the internet but could not find a picture.

    Egil, those the "tamper proof" bolts that BMW used. You can get them off with a good set of pliers. After you get them off, simply go to a nut & bolt store to match the thread and get the head in desired style (mine is allen key style). Just bring in all of the bolts from one DK motor, they are not all the same length or size.
    CB01718 850i Lagunengruen Metallic / Silbergrau Leder

  6. #6
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    Quote Originally Posted by Noggie View Post
    I was thinking about refubishing mine butI have a slight problem.

    My DK's are not put together with torx or phillips screws, but this strange tamper proof type I have not seen before, and I do not have a tool to open them.
    I was searching the internet but could not find a picture.
    I have the same on one of mine, and it looks like it can be screwed but not unscrewed, I've seen this type of screws on various ac/dc transformers. I managed to open the other one, but it looked new, commutator, gears and everything else.

  7. #7
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    here is another write up with more pics
    http://www.e38.org/e32/throttles/BMWThrottles.htm
    and the one from MWrench
    http://www.mwrench.com/Whitepapers/DKMotorcleanup.pdf
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  8. #8
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    bunch of broken image links in your latest write up...

  9. #9
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    that is not my write up, unfortunately the site does no longer work, that is what was saved, but still enough and good info
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  10. #10
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    Quote Originally Posted by wokke View Post
    To me it seems the butterflys themselves wear and I'm now having a set of DKs re bored and a new set of butterflys made. I hope this will cure my problem.
    Has anyone made similar experiences?
    I have found this to be a very usual condition, together with potentiometer wear.

    It is also probably THE most common cause of the tranny being set to 'limp home mode' because wear or dirt causes the throttle valve angles between the sides to differ more than they should, according to the very conservative engine management software in these old cars :-).

    I haven't actually seen so much wear of the valves or the bores. I have seen some pivot shaft wear but most problems come down to the intake being gummed up, so a good clean often solves the problems.

    That said, the carbon tracks in the potentiometers start to get worn out, and connector oxidation is becoming a real problem, not only in the engine compartment but all over these overly complex cars.

    I've just spent two days repairing an RM 1 relay module. It had several faults caused by humidity, including rusted relay return springs and corroded IC legs. I had to rebuild part of the PCB (corroded away) as well as replacing several ICs - plus of course all the electrolytic capacitors - something I do routinely each time I service a computer module.

    The quality of the connectors and wiring used in the E31s is not fantastic considering the type of car this is. I mean, the 850s are the best cars ever manufactured by BMW - perhaps they didn't realise it at the time.

  11. #11
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    the missing pics from the one linkI posted above are now on my website on the left under new and updated 09/10
    special thanks to revtor who saved them. He also stripped all layout codes from the HTML file. The original was created with Microsoft Word (the horror) and couldn't be read in a modern browser without images overlapping text and such. The cleaned HTML should work everywhere.
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  12. #12
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    Very interesting, thanks for sharing that info. Great to see someone repairing modules rather than swapping.
    Last edited by shogun; 05-11-2019 at 10:44 PM.

  13. #13
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    Just another trick to remove the "one-way" screws on the DK throttle bodies:
    Use a Dremel tool with the small cutting wheel and cut a slot straight across into the top of the screw head - then you can use a straight-blade screwdriver to easily remove the screw. A small hack saw will also work to cut the slot.

    Mark in mid-MO
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  14. #14
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    Any info on DK cleaning for the M73? Its a Siemens not Bosch design.

  15. #15
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    Quote Originally Posted by SanDiego850 View Post
    Any info on DK cleaning for the M73? Its a Siemens not Bosch design.
    If meanwhile someone has some info on the cleaning of Siemens DK's for the M73, let us know. Pics are of course always welcome.
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  16. #16
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    Quote Originally Posted by shogun View Post

    If meanwhile someone has some info on the cleaning of Siemens DK's for the M73, let us know. Pics are of course always welcome.
    I am working on one, if successful will post, however I have tried in the past with no luck. Siemens went out of their way to make sure these are not serviceable. M70 Bosh tried this also with tamper proof screws but thats as far as they went to make sure owners purchase new assembly at $1500 rather than try to refurbish...

  17. #17
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    More interesting stuff on throttle valves http://mastertechmag.com/pdf/1997/08...le_control.pdf by Lester Bravek

    DRIVEABILITY CLINIC - Electronic Throttle Control
    The EML
    BMW's fly-by-wire, EML throttle control was introduced in 1988 with the 750iL BMW and its 12-cylinder M70 B50 engine. The same engine is found in 850 models, also with EML (electronic throttle control). Although simple in concept—open throttle
    to speed up engine, or close throttle to slow down engine_electronic throttle control is in reality quite complex. It is linked to various controls units which interact with the EML computer to control throttle angle. These control units are: DME, EML, ABS/ASC+T, and EGS. The instrument cluster is also connected to the EML because it supplies a vehicle-speed signal. Integration of these control units provides total vehicle control during driving. The EML system is involved in the following operations:
    • Automatic throttle synchronization of both engine cylinder banks, throughout the engine speed range,
    • Integration with ASC to control vehicle stability,
    • Idle-speed control via throttle-plate-opening angles,
    • Cruise control without extra linkages or ECU,
    • Throttle-opening curves to match the EGS-program selection switch, and
    • Emergency failsafe operation.
    The EML computer controls the throttle-actuator motor based upon engine temperature, climate control, road speed, engine speed, braking input, ABS/ASC+T torque request, transmission shiftpoint directional current flow through the throttle motor
    winding opens or closes the throttle valve. During opening operation, the throttle motor is always working against closing pressure from the return spring. The mechanical closing force of the return spring provides failsafe operation in the event of a failure in the EML control system. The EML unit also employs sensors for feedback to monitor pedal position, throttle angle, and brake pedal activation. The EGS unit provides a low volt age signal to the EML unit whenever the "Sport" program switch is selected. The EML unit then adjusts throttle-opening curves to match the transmission's sporty shift characteristics. EML also plays a part in overall vehicle stability, by controlling maximum engine speed and vehicle speed. EML limits the engine speed to 6000 RPM by
    controlling maximum throttle-opening angles. Vehicle speed is also limited by closing the throttle valve before the maximum allowable speed is reached. The DME unit provides the TD signal for engine-speed limiting, while the instrument cluster
    provides the vehicle-speed signal. Note: depending upon the model year, the vehicle speed input may be provided either by the instrument cluster or the EKM (electronic body module).
    BMW Glossary of Terms
    ABS /ASC- Antilock brake w/automatic stability control
    ASC - Automatic stability control
    ASC+T -Automatic stability plus traction control
    DK - Throttle motor
    DKE -Engine output torque (throttle increase)
    DKR -Drag torque (throttle decrease)
    DME - Digital Motor Electronics (fuel injection)
    EGS -Electronic transmission control
    EML - Electronic throttle control
    FGR - Cruise control
    LL - Idle contact signal
    PWG - Pedal position switch
    TD - Engine speed signal
    Ti -Injector ON time
    VL - Full load contact signal

    Using two current probes across each wire to the idle motor shows a 1 msec current pulse through the DK valve at 5 amps peak. The current probe is set to lOmV/per amp, and each pulse shows a maximum of 50mV. Two current pulses are visible
    because current flow in a series circuit is the same amount through all parts of the circuit. The "on time" of this 5 amp pulse determines the opening force of the throttle valve. A gear reduction unit allows precise movement of the throttle plate.
    The heart of the system is the throttle-motor actuator (DK), located on each bank of the V-12 engine. The motor uses bi-directional current flow to open and close the throttle, according to various inputs received by the EML computer. Synchronization of
    both DK valves is carried out by the EML computer at idle. Based upon injector opening time (ti), the DK valves are positioned to have no more than 1.7° difference in throttle angles. The idle motor and harness connector terminals are gold plated.
    To open the throttle, power is supplied to one side of the DK motor (Channel B), while a 1 msec pulse to ground reaches the other side of the DK motor (Channel A). This forward current pulse works against the spring pressure in the DK motor. To close the throttle valve, the direction of current flow is reversed. Channel B is then supplied with a pull to ground pulse, while Channel A becomes the supply voltage to the DK motor. The reverse current flow works with spring closing pressure.
    The pedal-position sensor (PWG) is located above the brake pedal, near the steering linkage, and is connected through a linkage to the accelerator pedal. There's no direct connection between the accelerator pedal and the throttle plates, so a pair of dual-return springs inside the PWG sensor mimic the "feel" of a mechanical throttle-actuator. The EML unit monitors the accelerator pedal position via an internal potentiometer, a 9° switch and a safety switch wired to the brake switch.I have tested the position of the 9° switch by plot ting it versus the PWG potentiometer. Most throttles travel approximately 90° from a closed to open position, so I used an "if, then" statement to test for accuracy. If a throttle travels 90° in 400 msec, then 9° of throttle movement takes 40 msec. By using the PWG potentiometer readings in the guide, I was able to show the range of pedal travel as related to throttle travel and their relationship to the 9° switch. Formula: 90°=400 msec as 9° = 40 msec.

    The PWG sensor is really three sensors in one. The PWG potentiometer and the 9° switch give constant feedback of accelerator pedal travel to the EML unit. The EML unit provides a low voltage signal to DME units whenever the PWG voltage is low
    and the 9° switch is inactive. As an additional safety feature, the idle contact circuit is wired through the brake pedal switch. This is to ensure a hard to the DME units for fuel cutoff actuation, thus limiting engine speed.
    The brake-activation switch contains two switches in one housing, and is located near the PWG sensor underneath the dash. The EML monitors a switch that activates the brake lights when the pedal is depressed. The other switch works in conjunction
    with the released PWG pedal switch to provide an additional brake-pedal depressed/idle-contact input to the EML/DME control units. The voltage on the brake light input switch goes "high" while the brake pedal depressed voltage goes "low."

    The waveform above is the injector "on time" (ti) from one bank of injectors controlled by the DME unit. The EML unit is wired to the injector output stage from one bank of each of the DME units. By looking at the actual ti "on time" from each DME
    unit, the EML can reposition the throttle plates individually to achieve a balance between both sides of the" V-12 engine. The V-12 is treated like two separate 6 cylinder engines, each having its own DME control unit.

    It's a natural connection for the EML unit to also be responsible for cruise control. The EML helps eliminate the separate linkage or control unit found on non-fly-by-wire systems. The cruise control switch (FGR) is a two-wire, five-position control switch.
    The switch contains various resistor values for each position selected on the switch. The FGR is supplied with 5 volts and the EML unit recognizes the voltage drop across the selected resistor as a separate input function.

    The 3-tenninal sensor in the foreground is a dual-NTC thermistor. Separate sections of the thermistor are connected to each DME unit. The third terminal is a return ground. The NTC sensor in the back ground is used by the EML unit to determine
    engine temperature. One of the criteria for achieving throttle-valve synchronization is a coolant temperature that is 80° C or greater. The other function of the coolant sensor is to provide increased throttle response with colder engine temperatures.

    Always pull fault codes from the EML or DME computer(s) before starting on any driveability complaint. The AST 5510 provides fault-code access to both DME units, as well as the EML unit. The EML provides throttle-position information to the DME units. A fault code in the DME units for idle- or full-load contact could be traced back to the EML unit. A defective DK potentiometer angle or inoperative DK switch would be the root cause for a idle or full-load fault in all three units.

    The EML performs a self check when the ignition switch is first turned ON. The EML warning light illuminates for two seconds as a bulb check. If certain hard faults are detected, the EML warning lamp will stay on with a fault code stored in memory. Substituted values are provided for engine temperature, engine speed, and vehicle speed. Vehicle speed from the instrument cluster is sent to the EML unit. This signal is used for cruise control, vehicle-speed limiting, and idle-speed regulation.

    The ECU compartment box (e-box) is located behind the right-front shock tower. The EML unit uses a 55-pin connector similar to those found on DME 1.1 through 1.3 systems. Also located inside the e-box are both DME units, EGS unit and ABS/ASC control unit. This 1991 850i used an 88-pin connector on each DME control unit. A break out box was used to check the various signals going in and out of the EML unit (a JGM Automotive Tooling breakout box is shown here).

    The EML unit sends and receives signals to and from various control units, as it controls engine speed as related to overall vehicle stability. No matter how strong the engine is, you won't be able to do any smoky burn-outs by flooring the accelerator
    pedal. The EML unit determines the proper throttle opening to keep engine torque within acceptable levels. The ABS/ASC systems also send requests for torque reduction to the EML unit during cornering and braking to maintain vehicle stability.

    The above signal (DKE) is from the ABS/ASC control unit to the EML unit on the same 1991 850L It is a pulse width modulated signal from the ABS/ASC, requesting the EML to increase throttle angle (DKE). This signal was taken with the key ON, engine OFF, and is a 100HZ fixed frequency signal with a variable duty cycle. The DKE and DKR sensors both send fixed frequency variable duty cycle control signals to the EML unit from the ABS/ASC control unit.
    Last edited by shogun; 07-21-2016 at 07:15 AM.
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  18. #18
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    Thanks for bringing this to the top again. I was going to clean them this spring, and you saved me some searching (very nice write ups by the way).
    My Cars - 1991 BMW 850i - mine for fun, 1993 Saab 900c - mine for fun, 2008 Lexus is250 - my daily driver, 2003 Dodge Durango - my wife's, 1994 Acura Legend - gave it to kid

  19. #19
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    and here on Johan's site, Reconditioning BMW E31/E32 - M70 / 750il, 850i Throttle Assemblies http://bmwe32.masscom.net/moswald/75...ies/index.html

    from the E32 forum: M70 Dk Feedback Resistance Material /alternatives - Here is a company which repairs/modifies Maserati wiper material carbon track with a contactless system
    Contactless is the only way to go in future in my opinion, as the original system wears. Works basically similar to the contactless ignition systems which are offered for older cars nowadays. One day we will run out of used/traditionally rebuilt DK's.
    Might be worth to contact them, if they are interested to design such system also for the Bosch throttle valves for the M70 engines in E32 750 and E31 850. More business for them for sure than for the few older Maserati.
    https://www.bimmerforums.com/forum/s...l+carbon+track
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  20. #20
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    I was toying with the idea a few years ago (before life got in the way) to use an optical encoder and some simple electronics to replace what is basically a potentiometer. it'll last forever and will not lose calibration.

    power is already in the loom, it'll be plug and play.

    i still have the project notes somewhere... I'll just need to get off my ass... and find myself a cnc....

  21. #21
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    Thanks for the Write up Questions on Bolt Sizes

    Quote Originally Posted by Jenya View Post
    Egil, those the "tamper proof" bolts that BMW used. You can get them off with a good set of pliers. After you get them off, simply go to a nut & bolt store to match the thread and get the head in desired style (mine is allen key style). Just bring in all of the bolts from one DK motor, they are not all the same length or size.
    Great Write up Thanks

    Used Vise Grips to get the bolts out.

    Went to the HW Store and all they had for M6 Bolts was 1.0 Pitch which these definitely were not, Any Idea what size and Pitch and Length for all the Bolts

  22. #22
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    They are 6x40mm, 6x25mm, and 4x12mm - all 1.0 pitch, according to John Patterson (who successfully replaced them).
    '91 Dinan 860 Stage III (new 6L engine)
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  23. #23
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    I will verify the pitch in next day or two but M4 only comes in a .70 and a .50 pitch so I'm pretty sure they were .70 that I used. The M6 are 1.0 but I will verify that also.

  24. #24
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    On the German E31 forum there is a throttle valve DIY, under picture 5 there is mentioned that he replaced the old bolts with inbus bolts each 2x M10x40 and 4x M6x12, no pitch mentioned http://www.8series.eu/images/technik...pen_ueberholen
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