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  1. #1
    Member
    Join Date
    Nov 2015
    Location
    NW Georgia
    Posts
    17

    90HP 4-Stroke Acting Up

    I have a 2015 90 HP Merc 4-Stroke, 2B187022, that began losing power and running rough at cruise and WOT. After nursing it home, I can put the shifter IN NEUTRAL and rev to 2,500 rpm and the motor will shake violently but no alarm. But I can also put it IN GEAR and rev all the way to 5,000 rpm with no shaking, perfectly smooth. This is obviously not under a load since the boat is not in the water. I originally attributed the rough running to bad fuel so I replaced the low-pressure in-line fuel filter with the same results. Does 90 4-stroke have a rev limiter that kicks in around 2500 while in neutral only? If not, why would the motor run smoothly now but only in gear? Thanks for your insight!

    Bob
    Last edited by HighRez; 07-31-2017 at 04:48 PM.

  2. Member
    Join Date
    Jan 2006
    Location
    Saint Louis
    Posts
    1,245
    #2
    Yes, it has a Neutral rev limiter to protect the engine and do not run it at high RPM's unless in the water. My first thought would be the Fuel Supply Module (FSM). But I'm pretty sure they got those issues fixed with the later years. Take it to the dealer and let them figure it out. Should be under warranty. (Also responded to your other post in the Merc section).



    Rick

  3. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,941
    #3
    +1... never accelerate unless you are IN THE WATER and IN GEAR (going somewhere).

    Have your Spark Plugs ever been replaced? What other Annual Maintenance has been done?


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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