Page 1 of 3 123 LastLast
Results 1 to 20 of 58
  1. #1
    Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167

    1997 Mercury 200 EFI Misses Intermittently

    1997 Mercury 200 EFI
    Serial number OG570955

    This motor has run nearly perfectly for many, many years. I recently came across a broken down boat and towed them 3 miles back to the dock. I could only tow at 7 mph at 80% throttle the entire way. After dropping them off was the first sign of trouble, the engine was difficult to start and smoked more than usual once we got going. The smoke cleared up quick but the motor missed a few times for just a second at a time running about 40 mph. After that trip I changed the spark plugs and fuel filter and the next two trips had no trouble at all. I figured the plugs just loaded up from the tow. On the third trip the engine began to miss again while on plane and this has been randomly happening ever since over the past couple trips. I have about 8 hours on the engine since the tow. It can miss at low rpm too and has felt like it was bogging down for just a second or two only at low rpm. 90% of the time it runs perfectly well but then it starts to miss again. The miss is only for a brief second and full power comes right back so it feels electrical but it may do it 4 or 5 times in a row then not do it for the rest of the day. In retrospect, I should have towed them in at lower speed or maybe it was just a coincidence that the problems started then. So where is a good place to start diagnosing this issue given how it only happens intermittently? I generally do all my own maintenance and have the shop manual. Thanks!

  2. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #2
    What plugs did you use?


    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).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  3. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #3
    NGK 6431 BU8H. These are the same plugs I have been using since 2006 when I purchased the boat and motor

  4. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #4
    I pulled the new ones yesterday just to see how they look. All six were similar to the two pics below
    IMG_2508.jpgIMG_2513.jpg

  5. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #5
    Might be a good idea to remove and photograph the actual plugs that are in the engine. "New" does not (necessarily) equal "good".


    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).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  6. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #6
    Those are the actual plugs from the engine. By new, I meant the ones that have a maximum of 8 hours on them. They were installed 6 weeks ago after the towing incident and the engine began to act up.

  7. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #7
    Just to be clear, I regularly change the plugs and always use the NGK 6431 BU8H as specified in the shop manual.

  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #8
    No problem with the plug you are using. I suspect you may have some of them misfiring due to lines apparent (see one of the pictures exhibits this).


    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).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  9. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #9
    First, I appreciate you spend the time to help so many people on this board. Thanks!
    Do you mean misfiring because the plugs themselves are bad or because of another problem like maybe the ECU is not working properly?

  10. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #10
    I would be looking at the plugs themselves. Specifically lines formed in the porcelain of the surface-gap area.


    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).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  11. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #11
    Here are cylinders 1 through 6 in order. I did wipe them up a bit with a clean rag.
    Cyl 1.jpgCyl 2.jpgCyl 3.jpgCyl 4.jpgCyl 5.jpgCyl 6.jpg

    Looks like cylinder #5 does have an issue. This next pic below is another photo of the plug from cylinder 5 before I wiped it with the rag. The line shows up a bit better.

    Cyl 5 before rag.jpg

    Plugs 1, 2 and 3 look ok to me but I am not so sure about 4 and 6. I will just replace all six and see how it goes.
    Thanks again for all your help Don.

  12. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #12
    That's what I would recommend. Make sure you've got Quickare and Quickleen in your fuel as well... a tow like you did is really good for building up extra carbon.


    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).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  13. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #13
    Just picked up Quickleen and Quickare. I will report back
    Thanks!

  14. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #14
    First day out after replacing all six plugs with NGK 6431 BU8H and adding Quickleen and Quickare to the fuel, the motor still had the same issues. It was bogging down intermittently for just a second or two each time and then would run well for 5 miles and then do it again. I am going to bring out a portable fuel tank, hook it to the engine and see if it still has problems.

  15. Member
    Join Date
    Mar 2012
    Location
    Pelham, GA
    Posts
    2,004
    #15
    Sounds like a good idea, also if you have someone with you to use a timing light to check for spark when it’s sputtering, if it can be done safely. But sounds fuel related. It would be also great if you can find a known good ecu to use and see if that is the problem, bad fuel drivers etc in the ECU are not uncommon.
    Mercury 2002 200hp Carbed Saltwater
    OT566776
    2002 Cape Horn 22' Bay

  16. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #16
    Thanks for the tips leonreno

  17. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #17
    Additionally, take a real close look at the TRIGGER harness. Look for deterioration of the wiring, or the sleeve the wires run in.

    You can do a resistance test on the trigger- during each connection/test, move the throttle from idle to WOT and back to idle (slowly) several times, while monitoring for any significant changes (which could indicate a compromised trigger lead/wire).


    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).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  18. Member
    Join Date
    Nov 2006
    Location
    Sacramento
    Posts
    167
    #18
    Quote Originally Posted by EuropeanAM View Post
    Additionally, take a real close look at the TRIGGER harness. Look for deterioration of the wiring, or the sleeve the wires run in.

    You can do a resistance test on the trigger- during each connection/test, move the throttle from idle to WOT and back to idle (slowly) several times, while monitoring for any significant changes (which could indicate a compromised trigger lead/wire).
    I am still experiencing the same issues except the missing and bogging down is getting more extreme. Don I will perform the Trigger tests as soon as I am back on my feet following surgery. I hooked up a remote fuel tank and fished an entire day with it but the motor issues where still there so that eliminates some things. Last trip the engine bogged down at low rpm for a good 90 seconds before it would catch and quickly power up. With the throttle engaged the motor would quickly oscillate between full power and severely bogging down with my hand completely off the throttle. Eventually it would catch and then ran mostly trouble free for 10 miles or so while fishing several different spots. Then on my way back in the same thing happened all over again. I am wondering if the Trigger tests are normal should I be suspecting the ECU and think about sending it in for testing?

  19. Member Hez's Avatar
    Join Date
    May 2017
    Location
    Apopka, FL
    Posts
    2,886
    #19
    Quote Originally Posted by mac18 View Post
    I am still experiencing the same issues except the missing and bogging down is getting more extreme. Don I will perform the Trigger tests as soon as I am back on my feet following surgery. I hooked up a remote fuel tank and fished an entire day with it but the motor issues where still there so that eliminates some things. Last trip the engine bogged down at low rpm for a good 90 seconds before it would catch and quickly power up. With the throttle engaged the motor would quickly oscillate between full power and severely bogging down with my hand completely off the throttle. Eventually it would catch and then ran mostly trouble free for 10 miles or so while fishing several different spots. Then on my way back in the same thing happened all over again. I am wondering if the Trigger tests are normal should I be suspecting the ECU and think about sending it in for testing?
    I just went through similar issues with a 1996 175 hp EFI and it turned out to be the ECU needed to be rebuilt. My mechanic said these are notorious for having the fuel drivers come loose.

    Wishin' I was fishin'...


    1990 Ranger 374v
    1996 175 HP Mariner - Magnum EFI
    25p Tempest - A45 model
    80 lb 24v MinnKota Maxxum
    Humminbird Helix 10
    Humminbird Helix 7
    Garmin EchoMap 106sv w/ LS
    Dual 8' Power Poles



  20. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #20
    This oscillating RPM change: Was it consistently rhythmic or totally random?


    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).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

Page 1 of 3 123 LastLast