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  1. #26
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    Dumb question maybe but do these engines have acoustic knock sensors? If they do I'd expect some false positives under these high load conditions from the DMFW.

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    Click here to enlarge Originally Posted by ajsalida Click here to enlarge
    Dumb question maybe but do these engines have acoustic knock sensors? If they do I'd expect some false positives under these high load conditions from the DMFW.
    Yes, they do. But it's misfire --not knocking -- that is being detected.

    Neil

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    Add in the people who used sprung clutches with OE DMFW and theres another spung system to add to the mess.

  4. #29
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    Click here to enlarge Originally Posted by Sered Click here to enlarge
    You're misunderstanding what I'm saying; I'm quite aware that its a single spinning mass. It is still two masses separated by an insulator (that's called a capacitor) spinning over a stationary mass (the engine block).

    And the two masses are joined by springs? Not sure I follow you.
    it may.. kinda be what a capacitor is, but it won't have electrical capacitance (considering it's grounded).. and if it were, it's a problem that would happen on stock turbo cars (considering it's entirely RPM dependant)
    .. and the masses aren't totally separated (like... floating..) in the flywheel if that's what you are saying, they're still connected... so no the stock DMF isn't anything like a capacitor.. i'm very confused by what you're trying to say now

    - that's what i mean.

  5. #30
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    Click here to enlarge Originally Posted by rudypoochris Click here to enlarge
    I am pretty sure its just the flywheel "bottoming out" at a specific frequency the ECU determines to be a misfire. If you have stock DMFW and 16+ psi of boost with high timing below 3500 you will hear a pretty loud drone at WOT in gears 4-6. I believe this is the DMFW transmitting noise and vibration as its springs are being compressed and decompressed against the excursion limit. Once this limit is hit the two pieces of metal are essentially banging against each other which is then read as a misfire at some rpms. With stock turbos its very rare you will carry that much torque to 5500+ where this happens. On SMF this noise no longer exists since there are no springs to compress (besides the disc). That is my best guess anyway.
    Click here to enlarge Originally Posted by ajsalida Click here to enlarge
    Yes with all the associated issues of resonances of coupled spring-mass system, driven by a forcing function with lots of harmonics at firing rate, and then on top of that limited travel of the masses and them maybe bouncing off of each other at max min limits of travel. It is not surprising to me at least that you push HP/TQ more than double stock that such a system begins to get too noisy. Think of 6 hammers pounding twice as hard on a rotating shaft @ 6500 rpm and those poor little coupled dual masses bouncing around, it's going to start getting confusing trying to pull a reliable CPS signal off of it. Also there is a guibo further down the line and it has elastic torsional resonances too. Lot of wiggling going on.
    yeah, that's what my thinking would be, if the two flywheel masses bottom out rather aggressively, sensors would see the shock similar to a knock.

    this makes a lot more sense to me now (how a DMF could cause misfire sensors to go off).. at low speeds/power it dampens excellently, at higher speeds it's overwhelmed?

  6. #31
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    If I google "misfire cause" I get a lot of results regarding Powertrain. Saying that the OBDII system is fooled by vibrations and stuff.

    One of the drawbacks of using a crank sensor to detect misfires is that it can sometimes be fooled by normal powertrain vibrations. Driving on a rough road, for example, may produce variations in crank speed that seem like misfires but are not. Some OBD II systems monitor inputs from the ABS wheel speed sensors to tell when a vehicle is driving on a rough road, and disable misfire detection until the road smoothes out.
    Powertrain Misfire
    Sometimes, the engine has nothing to do with a misfire. One common cause for "jerky" performance that feels like a misfire is a problem in the transmission and its ability to properly up- or down-shift. If the misfire occurs during higher speeds, it could be a problem with the operation of the overdrive gear or a chattering clutch in the Lockup Torque Converter. If the vehicle jerks or feels like it is "missing" during deceleration, it could be due to harsh transmission downshifts, badly warped rotors, out of round brake drums, and/or sticking brake pads or brake shoes.
    One article says that tourque variations can cause the DME to trigger misfire codes because the DME thinks with the same amount of fuel and air there should be the same power output.
    BMW 335i xDrive MT
    COBB Stage2+|Wagner FMIC|CPe-Downpipes|BMW Performance Exhaust

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