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  1. #1

    Question 1994 Mercury 175 HP EFI Dropping 3 Cylinders

    I have a 1994 Mercury 175 HP EFI outboard that has an intermittent problem where it seems to be dropping 3 cylinders. It is not reliably repeatable. I have taken it to a dealer 3 different times and they cannot get it to act up long enough to find any problem. The symptoms are that it happens when being started, it will accelerate slowly to a plane and run that way for a couple of minutes then it will suddenly kick in on all 6 cylinders and take off. While it is running on 3 cylinders it runs hotter than when it is running on all 6. It does not happen everytime it is started. It does not happen repeatably after sitting for several days of after being run and shut off. It has never dropped to 3 cylinders after running on all 6. Needless to say it idles poorly when it is on 3 cylinders. Compression on all 6 cylinders is good. The fuel system has been replaced. I feel like it has to be an electrical parts issue. Any ideas?

  2. #2
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    5,559

    Default Re: 1994 Mercury 175 HP EFI Dropping 3 Cylinders

    Stator or switchbox..Need to check and see which side when it acts up..
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  3. #3

    Default Re: 1994 Mercury 175 HP EFI Dropping 3 Cylinders

    Quote Originally Posted by faztbullet View Post
    Stator or switchbox..Need to check and see which side when it acts up..
    Thank you. I suspected the same.

  4. #4
    Join Date
    Apr 2008
    Location
    Northwood, New Hampshire
    Posts
    20

    Default Re: 1994 Mercury 175 HP EFI Dropping 3 Cylinders

    Quote Originally Posted by berrymr View Post
    I have a 1994 Mercury 175 HP EFI outboard that has an intermittent problem where it seems to be dropping 3 cylinders. It is not reliably repeatable. I have taken it to a dealer 3 different times and they cannot get it to act up long enough to find any problem. The symptoms are that it happens when being started, it will accelerate slowly to a plane and run that way for a couple of minutes then it will suddenly kick in on all 6 cylinders and take off. While it is running on 3 cylinders it runs hotter than when it is running on all 6. It does not happen everytime it is started. It does not happen repeatably after sitting for several days of after being run and shut off. It has never dropped to 3 cylinders after running on all 6. Needless to say it idles poorly when it is on 3 cylinders. Compression on all 6 cylinders is good. The fuel system has been replaced. I feel like it has to be an electrical parts issue. Any ideas?
    I have the identical problem but it’s not dropping an entire bank. Last time it was doing it it was 2 cylinders on one bank and one on the other. I pulled the plug wires and have spark to all cylinders. Plugs are new this year. Any suggestions?
    Last edited by matt_moore; 09-25-2022 at 09:19 PM.

  5. #5
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    5,559

    Default Re: 1994 Mercury 175 HP EFI Dropping 3 Cylinders

    What year? What HP and how did you find it was 2 on one side and one on other?
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  6. #6
    Join Date
    Apr 2008
    Location
    Northwood, New Hampshire
    Posts
    20

    Default Re: 1994 Mercury 175 HP EFI Dropping 3 Cylinders

    Quote Originally Posted by faztbullet View Post
    What year? What HP and how did you find it was 2 on one side and one on other?
    1996 175 EFI

    I know that it was two and one because I pulled the plug wires while it was running on 3. Could hear which ones dropped and which ones didnít. But could hear spark jumping to the plug on all 6.

    Last night I ran it for about 10 mins and it never ran on 6. Itís usually only a 30 second to 1 min problem. Clears up randomly on its own.

  7. #7
    Join Date
    Apr 2008
    Location
    Northwood, New Hampshire
    Posts
    20

    Default Re: 1994 Mercury 175 HP EFI Dropping 3 Cylinders

    Ran it tonight, seemed fine for about a mile and then it dropped cylinders at WOT. It’s never done that before. Issue seems to be getting worse by the day.

  8. #8
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    5,559

    Default Re: 1994 Mercury 175 HP EFI Dropping 3 Cylinders

    Stop running it!!! If you have clogged injector those not firing are also not getting oiled! Need to check fuel pressure the send injectors and ECU to Brucato to have cleaned and tested.
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  9. #9
    Join Date
    Apr 2008
    Location
    Northwood, New Hampshire
    Posts
    20

    Default Re: 1994 Mercury 175 HP EFI Dropping 3 Cylinders

    Quote Originally Posted by faztbullet View Post
    Stop running it!!! If you have clogged injector those not firing are also not getting oiled! Need to check fuel pressure the send injectors and ECU to Brucato to have cleaned and tested.
    The oiling point is such an obvious point that I completely ignored. Thank you for the blunt reminder. Guess itís time to take it out of the water and get to pulling parts. Any rough idea of cost for the Brucato services you noted?

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