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Results 1 to 8 of 8
  1. #1
    Join Date
    Aug 2008
    Location
    Charlotte, nc,
    Posts
    82

    Default merc 1988 5.7 350 no spark/ how to check ign module for replacement?

    5.7 350 merc iv thunderbolt ignition. 1988 I replaced ignition coil and I still have no spark. How would I trouble shoot the ingnition module (they are expensive). trouble is it worked fine the last time I fired it up. Also the rotor looks fine and i have replaced the sensor about a year ago and it hasnt had hardly any run time. I have checked my grounds and all wire connections look fine. I am getting a 24v reading from the coil. Help please

  2. #2
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    2,753

    Default Re: merc 5.7 350 no spark/ how to check ign module for replacement?

    with key in the on position you should read 12V at the + side of the coil
    5.7 thunderbolt igitition no spark prob help - iboats Boating Forums

  3. #3
    Join Date
    Aug 2008
    Location
    Charlotte, nc,
    Posts
    82

    Default Re: merc 5.7 350 no spark/ how to check ign module for replacement?

    Quote Originally Posted by Bt Doctur View Post
    with key in the on position you should read 12V at the + side of the coil
    5.7 thunderbolt igitition no spark prob help - iboats Boating Forums
    sorry it was 12v. I did the following based on the book
    1. power from coil = yes
    2. power from red/white while connected =yes 5.6v
    3. power from green/white while connected = yes 5.6
    now book reads as follows.
    a. if no votage is noted (well i get voltage)
    b. if voltage in noted, replace ignition sensor.
    (The way i understand it if you get power from the previous step, then you skip to section 6.

    section 6. if battery votage is present at white/red disconnect coil wire and provide spark gap, then strike the green/white wire against ground. (i get no spark at this stage). I have replaced coil so book says its the ignition module. Sound like this is the problem??

  4. #4
    Join Date
    Oct 2009
    Location
    archer city, texas, us
    Posts
    186

    Default Re: merc 5.7 350 no spark/ how to check ign module for replacement?

    if that is the case get ready to spend some $$$$$$ been there done that good luck

  5. #5
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,329

    Default Re: merc 5.7 350 no spark/ how to check ign module for replacement?

    Tests for Thunderbolt Ignition:


    W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!


    Check the kill switch first!


    #1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

    #2 - If 12 volts are present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

    #3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

    #4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced.

  6. #6
    Join Date
    Aug 2008
    Location
    Charlotte, nc,
    Posts
    82

    Default Re: merc 5.7 350 no spark/ how to check ign module for replacement?

    Quote Originally Posted by Bt Doctur View Post
    with key in the on position you should read 12V at the + side of the coil
    5.7 thunderbolt igitition no spark prob help - iboats Boating Forums
    BT your thoughts on my latest post??

  7. #7
    Join Date
    Aug 2008
    Location
    Charlotte, nc,
    Posts
    82

    Default Re: merc 5.7 350 no spark/ how to check ign module for replacement?

    Sunday Bump

  8. #8

    Thumbs up Re: merc 5.7 350 no spark/ how to check ign module for replacement?

    Quote Originally Posted by danthemancarolina View Post
    sorry it was 12v. I did the following based on the book
    1. power from coil = yes
    2. power from red/white while connected =yes 5.6v
    3. power from green/white while connected = yes 5.6
    now book reads as follows.
    a. if no votage is noted (well i get voltage)
    b. if voltage in noted, replace ignition sensor.
    (The way i understand it if you get power from the previous step, then you skip to section 6.

    section 6. if battery votage is present at white/red disconnect coil wire and provide spark gap, then strike the green/white wire against ground. (i get no spark at this stage). I have replaced coil so book says its the ignition module. Sound like this is the problem??
    Hi guys I had some experience with 5.0 1990 Bayliner 27' thought I did everything right in checking spark but ended with a bad ignition switch. no spark while cranking. I pulled my hair out because it kept pointing to expensive ignition module or amp. Crazy huh. Got new ignition switch problem solved. Even when you have 12v at + side of coil when in on position.

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