Modifying Engine Computer for External "Smart" Ignition Coils

Discussion in 'Automotive Electronics' started by SliM3, Sep 30, 2016.

  1. SliM3

    Thread Starter New Member

    Sep 30, 2016
    2
    1
    Hello all:

    I have an '06 BMW M3 and am trying to run smart coils from the engine computer, which was originally set-up with embedded IGBT's. Basically I removed all 6 IGBT's from the board and ran the smart coils corresponding 5v and logic ground wires to the base and emitter pads. The primary coil grounds are batched together and run to a common ground stud in the engine compartment. I also jumped all the collector pads to the common coil ground source as well. My intention was to try and fool the DME into thinking it's still running the stock set-up, but have been unable to get a clean start. I'll get an occasional "bump" when starting, but no sustained run.

    I also hooked up my multimeter to the 5v signal and a common ground to see what the trigger voltage was, and I read between -0.92V to -11.28V. Needless to say my basic thinking is not enough to get my set-up running, so I'm seeking some guidance on how I could possibly get this to work? Any ideas? Thanks in advance for the assistance.



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  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    And what do you expect to gain from running a smart coil Vs the stock one?

    Until now I have never heard of a smart coil.
     
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Wouldn't yous till need the IGBT's of the ECM to switch the coils on and off in the correct sequence? Don't most ECM's work as a low side switch?
     
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
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    From what I can see from a bit of online reading is the smart coils use the stock ignition drive output of the MCU to trigger them so removing the stock MCU based IGBT devices serves no purpose. If anything it may be now either inverting the output signal or more than likely sending a 12 volt feed back from the Smart coils directly to your 5 volt logic drive since the stock system used a current sinking ignition coil drive system which is what the Smart coils are designed to work with.

    Seems like a purposeless and possibly MCU destroying mod to do.

    That and at $100+ a coil that's a pretty expensive mod to do unless there's a Nitrous system or other higher level engine mods in play that actually require the high output CDI power at the spark plugs.
     
    shortbus likes this.
  5. Papabravo

    Expert

    Feb 24, 2006
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    Did you come up with this on your own or are you following some random suggestion? Hope you didn't toast your ECU.
     
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  6. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I'll be surprised if he ever comes back. :(
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    Ummm. The narcissists are getting testy -- eh?
     
  8. SliM3

    Thread Starter New Member

    Sep 30, 2016
    2
    1
    Hey all, thanks for the replies and my apologies for not responding quicker.

    As for the "smart" coil analogy, it basically refers to ignition coils that have the transistors built-in. The engine has gone through an extensive rebuild, with the purpose of forced induction, hence the selection of a high power ignition system. The coils I'm trying to install have near CDI type output under the right dwell condition, so a huge jump in mJ output compared to the pencils. I also have a full complement of internal engine coatings, including thermal barriers on the pistons, combustion chambers, valves, ports, etc. Therefore I want to take advantage of running best rich torque AFR's while ensuring a complete burn and low HC emissions output.

    This has never been accomplished on the stock BMW DME, so this was also a bit of challenge to myself in trying to get them to work. We've made tremendous strides over on the ///M forums, backwards engineering our DME's and have full tuning capabilities now, which was once only reserved for the specialized tuners.

    So far I have not destroyed the DME, though I do have three of them laying around.

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    Last edited: Oct 2, 2016
    tcmtech likes this.
  9. tcmtech

    Well-Known Member

    Nov 4, 2013
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    WOW! Best follow up reply relating to 'Why are you doing this?' ever! :D
     
  10. jasone

    New Member

    Nov 2, 2015
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    Do you have a link to your ignition coils? I am familiar with how Toyota and a few other brands controls there coils. Coil has 12V, ground, a 5V command, and a 5V confirm circuit correct?
     
    Last edited: Oct 3, 2016
  11. jasone

    New Member

    Nov 2, 2015
    21
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    [​IMG] This is your current setup before the mods correct? I am not a BMW tech but I do work on cars everyday. Only thing I can think to compare you smart coils to is the Toyota style I have a few scope pictures and other info that sounds similar to what you have going on. I can post that info if you'd like.
     
  12. jasone

    New Member

    Nov 2, 2015
    21
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    [​IMG]

    I cannot find a known good scope pattern on an m3 but I did find one on a 330i. It has the multi spark at low RPMs. Could this be effecting your coils output if the M3 uses the same control? Is it possible your new coil cannot "keep up"? I can only think of simple (dumb) 2 wire coils that run the multi spark control.

    ...........Its a slow day at work and I have nothing better to do.
     
  13. bwilliams60

    Active Member

    Nov 18, 2012
    725
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    Have you looked at AEM or Performance Electricals controller?
     
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