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  1. #1

    Default 1989 50 HP Force Voltage Drop

    Hey everyone,

    I've been working on this engine for years on and off in my freetime, and I'm learning as I go. Yes, years. Every time I make progress, I run into another problem, but i'm not stopping until my engine is purring.

    Heres the current problem. When I try to start the engine my starter spins, and turns the flywheel, but doesn't turn it very quickly. It turns about 3/4 of a full rotation, then struggles to go the last 1/4 of the way (I guess because its harder to turn as the pistons are compressing) and then the cycle starts again. I've recognized the problem as a voltage drop, and in troubleshooting i've replace my battery, battery cables, and starter solenoid.

    Before those replacements, I was getting a drop of about 12.6 v down to 8ish volts upon turning the key, and with each subsequent replacement and cleaning of wires over time, the voltage would inch up by half a volt of so. I'm now at about 9.8v. I'm measuring this voltage at the starter solenoid on the post the battery is connected to. For the life of me I can't figure out what is causing the drop. Every component up to the point im measuring is new.

    Could it be the other wires that are connected to the starter solenoid? Theres the wire that sends the starting signal to the post the battery is connected to, theres a wire (called the interlock switch wire apparently) thats on a side post, and theres the cable that goes to the starter itself. Theres a tiny bit of corrosion on the starter cable, but it doesn't seem too bad and I was thinking it couldn't be the problem because I was testing the flow before the current reached that point. Now I'm starting to be more suspicious of that thought. If its not that, does anyone have any thought as to what it could be? (Also I forgot to mention that the starter itself is new as well.)

  2. #2
    Join Date
    May 2010
    Location
    Sebastian ,Fl
    Posts
    3,085

    Default Re: 1989 50 HP Force Voltage Drop

    Very FIRST thing you do is a compression test.
    The uneven comp on one cyl. can do exactly
    what you describe.

    The gearcase: if the bearings are corroded??
    Then it can do this too

    Lastly the battery if it has a dead cell?
    Or the cables bad or not grounded or
    the connections not tight.
    Again the same problem.

    Post the compression results???
    PLEASE,NO PERSONAL MESSAGES IF THE QUESTION CAN BE ASKED ON THE OPEN FORUM
    88 Bayliner with 2002 225 HP Mercury
    Buy American made Cars and Trucks!!!Towing insurance,get it.
    In Scenic Beautiful Sebastian by the sea Florida

  3. #3

    Default Re: 1989 50 HP Force Voltage Drop

    Thanks for the reply Jerry,

    I did a compression test and the results were kind of inconsistent, but the average for each one was around:

    Top Cylinder: 75PSI
    Bottom Cylinder: 60 PSI

    It may have been a fluke but on one of the first tests I did on the top cylinder, I got two or three full, fast flywheel rotations and the PSI gauge read approx. 125 PSI, but I couldn't replicate it.

  4. #4
    Join Date
    May 2010
    Location
    Sebastian ,Fl
    Posts
    3,085

    Default Re: 1989 50 HP Force Voltage Drop

    How was the test performed?
    You need to remove both plugs and
    use a screw in type pressure tester.
    Push the throttle all the way forward.
    If you use the key to turn the motor
    over? the plug leads need to be
    grounded and the Neutral safety
    switch jumpered.
    I added a pic of the octopus I made
    for grounding the plug leads.

    Easiest way: If you use the solenoid and jump it
    from there, you don't need the octopus
    or ground the leads.
    Attached Images Attached Images  
    PLEASE,NO PERSONAL MESSAGES IF THE QUESTION CAN BE ASKED ON THE OPEN FORUM
    88 Bayliner with 2002 225 HP Mercury
    Buy American made Cars and Trucks!!!Towing insurance,get it.
    In Scenic Beautiful Sebastian by the sea Florida

  5. #5

    Default Re: 1989 50 HP Force Voltage Drop

    For the test I unscrewed both plugs, and used a screw in compression tester.

    I'm not sure if this was implied well enough in my OP, but the engine doesn't run.

    Do I push the throttle forward while I'm turning the key? I thought the controls had to be in neutral to start? Is that what jumpering the neutral safety switch allows for?

  6. #6
    Join Date
    May 2010
    Location
    Sebastian ,Fl
    Posts
    3,085

    Default Re: 1989 50 HP Force Voltage Drop

    Throttle all the way forward and yes jumping
    the N safety allows the key to be used.
    Very important to ground the plug wires.
    They say that you can blow the packs if the
    leads aren't grounded.
    Or jump it at the solenoid.
    That way the plug wires don't need to be grounded.
    The throttle all the way forward doesn't really
    need too done either(my opinion) it makes no
    difference.
    If the readings aren't above 125 on one cyl?
    Then find another gauge and try again.
    PLEASE,NO PERSONAL MESSAGES IF THE QUESTION CAN BE ASKED ON THE OPEN FORUM
    88 Bayliner with 2002 225 HP Mercury
    Buy American made Cars and Trucks!!!Towing insurance,get it.
    In Scenic Beautiful Sebastian by the sea Florida

  7. #7
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    8,515

    Default Re: 1989 50 HP Force Voltage Drop

    Don't forget the negative side connections while looking for your voltage drop....another thing to consider is making voltage drop measurements across each item in the high current (starter circuits) paths. Using a single reference point will help in eliminating false measurements.

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