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  1. #1
    Join Date
    Aug 2008
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    Charlotte, nc,
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    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
    5,131

    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,
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    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
    10,396

    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.

  9. #9

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

    Quote Originally Posted by danthemancarolina View Post
    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


    My symptoms were the same and the ignition module was plugged in but the purple wire and gray wire to it were not plugged and the engine ran . I cannot figure that out please comment thank you P

  10. #10

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

    I did the cheks on #1 I am onlygettin 11.2 volts everything else is new sll no fire is t the ingnitr..??


    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.
    [/QUOTE]

  11. #11

    Default 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??
    yes that would point to ignition module per the merc manual . They are pricey but the Tbolt ignition is otherwise a very good system, with very hot spark.

    when I repowered my boat a couple years again I bought two of the 5.0 alpha modules and sold my old v6 module for about $200 each. I think with a lot of cracked blocks you end up with otherwise good used modules. If you can test it out right away you can see if it works.

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