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  1. #1
    Join Date
    Sep 2016
    Location
    Ashtabula, ohio
    Posts
    18

    Default Mercruiser 5.7 running on 7 cylinders

    Hi, I have a 1990 larson san marino with a mercruiser 5.7 in it. Bought it last year in the fall and just got the plugs changed on it this week and the shop said it's running on only 7 cylinders. They said they are not getting and spark from the cap for that cylinder. They tried new wires and nothing. Any thoughts on what it could be? Thank you.

  2. #2
    Join Date
    Jun 2006
    Location
    Spotswood, NJ, USA
    Posts
    4,337

    Default Re: Mercruiser 5.7 running on 7 cylinders

    if its the flat dist cap, replace it

  3. #3
    Join Date
    Sep 2016
    Location
    Ashtabula, ohio
    Posts
    18

    Default Re: Mercruiser 5.7 running on 7 cylinders

    I'll have to check it out, it's still at the shop haven't decided if I was gonna have them go thru it or work on it myself

  4. #4
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    10,196

    Default Re: Mercruiser 5.7 running on 7 cylinders

    Quote Originally Posted by Jsucci View Post
    Hi, I have a 1990 larson san marino with a mercruiser 5.7 in it. Bought it last year in the fall and just got the plugs changed on it this week and the shop said it's running on only 7 cylinders. They said they are not getting and spark from the cap for that cylinder. They tried new wires and nothing. Any thoughts on what it could be? Thank you.

    The ignition coil doesn't know which spark plug wire it is sending spark to.
    The sensor unit doesn't know or care either.
    The distributor cap does have an important involvement....... has the cap been replaced?
    If this is a Merc TB photo-eye triggering system....... the photo-eye wheel may be defective..... has anyone checked this?


    If this is truly an issue with NO spark being delivered to #7 cylinder, and yet you have good spark to all other cylinders...... and if this shop cannot figure out why........ I would quickly find a new shop before they end up replacing everything at YOUR expense!



    .
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  5. #5
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    15,708

    Default Re: Mercruiser 5.7 running on 7 cylinders

    Damn good advise!

    Jeff

  6. #6
    Join Date
    Jun 2008
    Location
    Island Heights, NJ,
    Posts
    2,918

    Default Re: Mercruiser 5.7 running on 7 cylinders

    re: " and if this shop cannot figure out why........ I would quickly find a new shop before they end up replacing everything at YOUR expense! "

    I would amend this to say... "If they could not figure it out the first time....I would quickly find a new shop." I would not give this incompetent ( kindest comment) or dishonest shop another shot.



    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280
    1972 22ft Bristol
    Honda 7.5HP 4 stroke Long shaft

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