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Results 1 to 14 of 14
  1. #1

    Default mercruiser 5.7 coil wire

    my 5.7 doesn't start,
    I am not getting spark to the distributor.
    since my tester is after the coil wire I decided to put my multimeter on that wire.
    I get no continuity, which maybe is expected? I read in other places that that may be the case?
    I also, get infinite resistance? how can that be?
    does anyone know what the resistance of that wire should be?
    (honestly before googling I would have expected zero)

  2. #2
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    5,531

    Default Re: mercruiser 5.7 coil wire

    Your description leaves a lot to the imagination...you might try adding some details...remember - we can't "see" what you can so we only have your posts to go by...

    If you are referring to the high voltage coil wire, it should have electrical properties like the spark plug wires...depending upon their vintage, they should show a resistance around 4000 ohms/foot.

  3. #3

    Default Re: mercruiser 5.7 coil wire

    thanks for the reply about the coil.
    I had thought that was just a wire.

    as for my other issues.
    I am reaching my limit.

    when I turn the key on - I get the normal beep, and the fuel pump turns on.
    I do get fuel pressure at the throttle body.
    boat will not start - even with starting fluid.
    I get no spark.
    I have checked my fuses - all were and are fine.
    I get 12V at my coil and at my ignition sensor
    I have replaced the ignition sensor in the distributor...
    if I manually ground the coil via the purple wire going to the ignition sensor the coil will fire (to ground with a spark tester)
    If I put a spark tester inline between the coil and the distributor - I get nothing
    and nothing at the spark plugs themselves.
    I have tried a new coil, which made no difference, so I left the old coil on.

  4. #4
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    6,963

    Default Re: mercruiser 5.7 coil wire

    The Merc Thunderbolt ignition coil is proprietary.
    These values may not be correct..... but this will give you an idea of how/where to test.
    See your OEM service manual for these values.














    Last edited by RicardoMarine; 08-03-2013 at 08:01 AM.
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  5. #5
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    2,621

    Default Re: mercruiser 5.7 coil wire

    "if I manually ground the coil via the purple wire going to the ignition sensor the coil will fire (to ground with a spark tester"


    The purple wire is what supplies the 12v and goes to the + side of the coil. ,so how are you getting a spark?
    green/white and red/white come from the dist, there is no purple going to the sensor. there are 2 grey wires on the neg side of the coil. 1 goes to the ign module ,the other goes to your tach. tach
    could be bad or the shift interupter is activated killing spark.
    Last edited by Bt Doctur; 08-03-2013 at 09:15 AM.

  6. #6

    Default Re: mercruiser 5.7 coil wire

    We want a year, and ignition example: thunderbolt ?

    We now know you have throttle body.

    So remove the 2 grey wires. You just want to start the engine right now correct. Put water to the drive the impeller will last most 30 seconds with no water going to the drive.

  7. #7

    Default Re: mercruiser 5.7 coil wire

    the boat is in the water... so no worries there
    its a 2000 thunderbolt ignition

    there is only one white wire going to the negative side of the coil.
    I have read a couple times to remove the tach wire from the coil - but there isn't one?

    I have heard about the shift interrupter, I don't have one on the block where the shift cables from the drive connect with the shift cables from the teleflex drive unit.
    is it possible that I dont have that switch? is there anywhere else it could be?

    there is a procedure in the manual for testing the coil.
    the procedure is to remove the coil wire from the distributor and put a spark tester on it attached to a ground.
    then disconnect the green/white wire from the ignition sensor. then with the wire that the green and white wire were connected to (i think its purple) tap it to ground - when I do that, the coil does fire.

  8. #8
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    2,621

    Default Re: mercruiser 5.7 coil wire

    the boat is in the water... so no worries there
    its a 2000 thunderbolt ignition

    there are 2 types IV and V

    There is only one white wire going to the negative side of the coil.
    I have read a couple times to remove the tach wire from the coil - but there isn't one?

    If you have a tach, theres a wire for it

    I have heard about the shift interrupter, I don't have one on the block where the shift cables from the drive connect with the shift cables from the teleflex drive unit.
    is it possible that I dont have that switch? is there anywhere else it could be?

    Is your drive a Alpha ,(uses one) or Bravo(does not use one.

    http://www.boatfix.com/merc/Bullet/94/94_02.pdf

    engine serial number , type of drive, type of ign system is it carb, MPI,TPI ,ECM controlled
    Last edited by Bt Doctur; 08-03-2013 at 02:33 PM.

  9. #9

    Default Re: mercruiser 5.7 coil wire

    not sure which thunderbolt type, how can I tell?

    so the white wire from the negative side of the coil joins 2 wires in the harness.
    1 goes towards the ecm
    1 to a connector which it appears connects to a gray wire - there is a gray wire at my tach.
    I am hesitant to cut that wire...

    its a bravo 1 drive, throttle body, ecm controlled.

  10. #10
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,278

    Default Re: mercruiser 5.7 coil wire

    The year of the boat should tell us what you have...TB IV is from the 80-90s. It will have the amplifier attached to the port exhaust manifold. Not sure when it became TB V. I think its module is attached to the side of the dist.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

  11. #11
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    2,621

    Default Re: mercruiser 5.7 coil wire

    Makes a big difference knowing that info.

  12. #12
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    2,621

    Default Re: mercruiser 5.7 coil wire

    A word of caution, dont try any testing untill you have the correct manual .ECM `s are expensive and some are NLA ,shorting, grounding, applying 12V or using the wrong type of test light
    will bite you in the wallet.

  13. #13

    Default Re: mercruiser 5.7 coil wire

    based on this - it's a thunderbolt IV
    http://www.boatfix.com/merc/Servmanl/18/18B4R2.PDF

    it's a 2000 boat...

  14. #14
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    2,621

    Default Re: mercruiser 5.7 coil wire

    Last edited by Bt Doctur; 08-03-2013 at 10:03 PM.

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