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Thread: M70 DK feedback resistance material repair possible?

  1. #1
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    M70 DK feedback resistance material repair possible?

    My wrenching buddy has an Alpina B12 E32 with the M70 engine. Idle is not the best, the rest is fine, nothing to complain about the power. We just finished re-sealing the intakes and re-setting the timing, new spark plugs, new fuel hoses in engine bay, new ignition wires, new ignition coils, new fuel pumps, new fuel regulators, fuel injectors tested, new engine ground cable, tested CPS, CID, MAF etc pp.
    All is fine except the idle, it goes slowly up and down.
    Having read about the throttle valves, we also cleaned them up as good as we could. But we assume the problem could be the black stripes of resistance material where the wiper makes contact with the resitance material, especially in that area where the wipers run most of the time, idle position.
    MWrench writes:
    The black stripes are resistance material that is deposited on a substraight. Attached to the throttle body shaft is a set of wipers that make contact with the resistance material. The wiper position is preset at the factory. As the throttle plate moves, the wipers also move along the resistance material and the resistance value changes.
    Major concern on this DK set is the amount of wear on the resistance material. When the wipers wear thru the resistance material, the resistance readings sent back to the EML will not longer be correct or may fluctuate wildly during throttle plate movement. This certainly would set off the EML light and may initiate “limp home” mode More here, see especially the last pic http://www.mwrench.com/Whitepapers/DKMotorcleanup.pdf

    Easiest would be to replace the throttle valves, we have plenty on stock, but that would be too easy, we would like to find a way to repair this area of resistance material.

    Did somebody already do that? How? Which material and procedure?

    Test procedure for the DK is on my website in German and English, someone on the German forum got these data from Bosch in Germany years ago, see http://twrite.org/shogunnew/topmenu.html reference data >>>>control systems>>DK input details, there is a small pdf file
    Last edited by shogun; 07-24-2018 at 05:50 AM.
    Shogun tricks and tips for the E32 series are HERE!

  2. #2
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    Shogun, this is what I specialize in when rebuilding the throttles.
    It's the main problem with these DK motors, anyone can clean them up but that does not help when the feedback from the open encoder is wrong.
    My approach is to move the encoder whiskers fraction of the mm at a time so they hit unused encoder surface then re test each time to see if the fluctuation was reduced till they are close to factory spec as possible.
    It's a precise and time consuming procedure to say the least but it works.
    That said throttles can be rebuilt this way only once, no replacement surface material works, I tried several, it's not hard enough and wears fast. I have commissioned an encoder manufacturer in the past to reverse engineer this open encoder design with the Bosch spec sheet you have in your post, after much back and forth it was not worth doing financially.
    Last edited by dragon850; 05-05-2018 at 09:47 AM.

  3. #3
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    Thanks, the way you do it is exactly what has been proposed more than 10 years ago on the German forum and we have done that already on some DK's before to move the encoder whiskers a fraction of the mm at a time so they hit unused encoder surface.
    That works, but I hoped meanwhile someone had found a solution to replace the surface contact material with a long lasting material.
    Shogun tricks and tips for the E32 series are HERE!

  4. #4
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    Here is a company which replaces Ferrari DK wiper material carbon track with a contactless system: Fixing the Maserati's Throttle Body - Wheeler Dealers https://www.youtube.com/watch?v=w2FMq5DEvQU
    The website of the company http://www.maseratished.co.uk/

    That might be the solution.
    Reminds me of the installation of an electronic contactless ignition in 2CV Citroen, also https://www.youtube.com/watch?v=wBvt1SbEFes
    Shogun tricks and tips for the E32 series are HERE!

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