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  1. #1
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    2011 Mercury 115 4 Stroke - bogging down at mid/high throttle

    I have a 2011 mercury 115 HP four stroke serial number 1B843908

    Started with having problems with bogging down at speed. It would troll all day long but sometimes and only sometimes at increased speed it just does not want to go.

    Where I have gone so far........
    1) Had the old foam style air filter, replaced with newer mesh style
    2) Since it was fine at slow speed’s I was thinking it was not getting enough gas and changed both fuel filters
    3) Change all spark plugs
    4) Drained fuel pump separator to check for sludge...nothing
    5) Check fuel lines for collapsing, look good.
    6) Its an EFI so I put a new battery in.

    Ive run it in between each step to test. Yesterday was the newest test with the battery. Started right up, idled perfect at the dock while I parked the truck. Backed up and sounded great, hit the gas and instantly knew it wasnt right. Backed off and she shut down, wouldnt restart. Back to dock with the trolling motor. Took it home and put muffs on. I can get her started again but doesnt stay running. Seems Im headed backwards, not closer to a solution.

    Any ideas?

    Thanks,
    Dave



  2. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #2
    Try a portable fuel tank with it's own separate fuel line, connected DIRECTLY to the engine.

    Do not use any portion of your CURRENT fuel supply system (components outside engine cowling).

    See if the problem persists.

    If it does, need to monitor FUEL PRESSURE and record what is happening.

    Also- what's the Maintenance History?


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #3
    something positive today
    I decided to go back through everything again. After trying to start a couple of times and hearing the fuel pump kick in I disconnected the first fuel filter just inside the motor. It had no gas. This tells me the fuel pump wasn’t sucking it up or there was a clog. Disconnected the fuel line between the motor and the deck where it leads to the main fuel tank. When I tried to blow through the line I couldn’t. Nothing getting through. Replaced the fuel line and bingo! Fuel pumped sucked up gas and she fired, ran good. No clue how I missed this before.



    Back to the launch, started and ran well but not superb. Was able to run all the way to full throttle and did for around 30 minutes up and down the river.
    BUT..... I’m not getting the acceleration or top end I’m used to. RPM are a good 800 ish short of what it will normally do and overall speed was 5-7 mph short of normal.


    Back home and pulled the plugs. All have a decent amount of carbon build up, 3 tips are white and one totally black.


    I’m getting somewhere but not home free yet! I keep looking.
    To be continued.....

  4. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #4
    I'd go back and replace ALL fuel line, direct from the tank to the engine. Also replace FUEL FILTERS (all).

    Install the new plugs and report back.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #5
    Quote Originally Posted by EuropeanAM View Post
    I'd go back and replace ALL fuel line, direct from the tank to the engine. Also replace FUEL FILTERS (all).
    Install the new plugs and report back.
    The boat is a 2011 Lund Tyee.
    The hose from the rear deck fitting to the motor was the one I replaced, it was that lighter weight gray Mercury hose about 4ft long.
    On the other side of the fitting to the tank maybe quite a bit tougher to get to and is the heavier black in a larger diameter.
    I replaced both fuel filters in the engine and have new plugs already. I dont think there is a filter in tank.

  6. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #6
    Roger that. Make sure the new line was heated at the ends (piping hot water in a coffee cup works well) so as not to grab and damage the inner liner when installing.

    See how it does after the plugs are replaced.


    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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    #7
    Quote Originally Posted by EuropeanAM View Post
    Roger that. Make sure the new line was heated at the ends (piping hot water in a coffee cup works well) so as not to grab and damage the inner liner when installing.
    See how it does after the plugs are replaced.
    Thats exactly what I did with microwaved water. The update from Saturday was with the new line and new plugs.

    I’m not getting the acceleration or top end I’m used to. RPM are a good 800 ish short of what it will normally do and overall speed was 5-7 mph short of normal.

    Back home and pulled the plugs. All have a decent amount of carbon build up, 3 tips are white and one totally black. That was kinda strange

  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #8
    How does the engine idle? Seem to be loading up or smoking at all?

    First item that comes to mind is the pressure regulator reference hose.


    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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    #9
    Quote Originally Posted by EuropeanAM View Post
    How does the engine idle? Seem to be loading up or smoking at all?

    First item that comes to mind is the pressure regulator reference hose.
    Ive been praying I dont have to get into that FSM!! I was thinking my first step would be to add in some SeaFoam or Quickleen and run a good few gallons of gas through her. That hose jumped me so far from where I was that Im wondering if she needs a good cleaning. Cant hurt

  10. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #10
    Perhaps... but if the problem is the reference hose, cleaning won't help.

    Can you answer the first sentence of Post #8?


    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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    #11
    Quote Originally Posted by EuropeanAM View Post
    How does the engine idle? Seem to be loading up or smoking at all?
    Ok, just ok. Now as smooth as usual. No smoking. Im not sure what "loading up" means. I have a couple videos of it running both on the water and at home on muffs but dont see a way to load them here

  12. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #12
    You would need to post them to a hosting site (such as Youtube), and then provide a link.


    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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    #13
    Quote Originally Posted by EuropeanAM View Post
    You would need to post them to a hosting site (such as Youtube), and then provide a link.
    It took a little doing but I got it!

    First time idol to full throttle Sat 6-16



    Another idol to full throttle after about 15 minutes of running



    In Driveway After Test Run Sat 6-16

  14. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #14
    Dave:

    Failed to see anything abnormal in the videos- other than perhaps not running very smoothly at idle (which is hard to distinguish via video/speaker).


    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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    #15
    Quote Originally Posted by EuropeanAM View Post
    Dave:
    Failed to see anything abnormal in the videos- other than perhaps not running very smoothly at idle (which is hard to distinguish via video/speaker).
    What would be your next move if you were me? Do you think running some good fuel system cleaner through it and time on the water would be worth it?

  16. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #16
    I think it would be a good idea to go back to the basics.

    -Compression Test

    -Spark Test (also confirm what brand, part number, and gap spark plug you're using). I know you said you replaced the plugs- be SURE on this.

    -INSPECT coils/boots for damage

    -Fuel Quality, Pressure and Delivery Tests.


    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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    #17
    Quote Originally Posted by EuropeanAM View Post
    I think it would be a good idea to go back to the basics.
    -Compression Test
    -Spark Test (also confirm what brand, part number, and gap spark plug you're using). I know you said you replaced the plugs- be SURE on this.
    -INSPECT coils/boots for damage
    -Fuel Quality, Pressure and Delivery Tests.
    -Confirmed proper recommended plug and gap are being used
    -Fuel is good now and pressure seems good
    -coils and boots look like brand new.
    -the whole motor really looks like brand new

    the one question I had is on the high pressure fuel filter. The manual says “should only be serviced by an authorized dealer” but I went ahead and changed it. Just pops out with the clips. I think they say that because under pressure a little gas can spew out but I just wrapped an old rag around it before I popped it out.

    Is is there more to that than I thought and maybe I did something there?

  18. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #18
    No- it's pretty straightforward to replace, as long as the fuel pressure is relieved.

    Lots of items "look like brand new" but don't function that way.

    Have you performed a loaded spark test, compression test, and/or leakdown test?


    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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    #19
    Quote Originally Posted by EuropeanAM View Post

    Have you performed a loaded spark test, compression test, and/or leakdown test?
    No I have not. 6 week wait at the shop

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    #20
    Quote Originally Posted by EuropeanAM View Post
    No- it's pretty straightforward to replace, as long as the fuel pressure is relieved.

    Lots of items "look like brand new" but don't function that way.

    Have you performed a loaded spark test, compression test, and/or leakdown test?
    I went and bought a compression tester.
    Top to bottom as follows:
    #1 148
    #2 150
    #3 148
    #4 150

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