MisFire above 4000RPM after 20 min

Discussion in 'Sterndrives' started by Beech2000, May 1, 2007.

  1. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member


    Check the coil for for hairline cracks and Megger the coil. I've had this problem in a car, and it was a real head scratcher.
     
  2. Beech2000
    Joined: Jul 2006
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    Location: Atlanta, GA (USA)

    Beech2000 Senior Member

    Excellent idea. Strange if it ends up being the coil since the previous engine
    had no misfire at power.

    I guess this engine is could more demanding of ignition parts though. I will let you know and thanks
     
  3. Beech2000
    Joined: Jul 2006
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    Location: Atlanta, GA (USA)

    Beech2000 Senior Member

    Mothers day disastor

    Replaced coil Friday and ran perfect all day Saturday. Today; not so lucky.

    Running up river for about 30 min on between 3500 and 4200. All was fine and then she shut down ending the day early.

    My first inclination was to reinstall the old coil. Unfortunately it was in such bad shape from leakage that I tossed it. So no backup on lake with no open parts stores at marina's.

    Getting 11 volts to the coil but no spark.

    Then I checked to make sure rotor rotate while cranking and it was. I should have known it was turning as I have oil pressure reading while cranking.

    The manual say's if 10 to 12 volts at + side of coil then check for grounding of - side. With ignition switch turned off I read .9 meg and fluctuating. suspect the tach was the reason for fluctuations. A

    Anyway the manual then say's skip to step 7 which is to check the coil.

    The replacement coil resistance was in limits per the seloc manual. 1 ohm between low side and over 2K on high. I assume this is true.

    The only item left is the sensor inside of the distributor. The ignition system is thunderbolt 4.

    Has anyone had these sensors go bad?

    I pulled device out and inspected. There are no signs of overheating or anything obvious. I checked distributor once again to make sure it was free of oil and again dry as a bone.

    Any details on Mercruiser’s thunderbolt 4 ignition system are greatly appreciated.

    Oh by the way I inspected the cylinders on Friday using borescope and no metal to metal contact as previously discussed. I don't know what detonation looks like but don't see any anomalies. How can I post the pictures on this forum?
     
  4. StianM
    Joined: May 2006
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    Location: Norway

    StianM Senior Member

    You can use a service like photobucket.com to upload your photos and then you use my pictures adress [IMG/]

    The ignition sensor send some kind off signal out. I gues you can see some kind off object that pases the sensor at certain intervals during a revelution.

    Try to use a multimeter Ohm on the sensor wile you try to simulate the sensor and see if you get a reading. If no try again using mV. I gues it't digital and will give 1 signal as long as it's not activated and 0 when it is or the other way around, it could also be generating a low voltage when it's pased by a magnet.

    I'm no expert on ignition systems, but I would asume this is the way to do it from my previous experience on other electrical systems.
     
  5. Beech2000
    Joined: Jul 2006
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    Location: Atlanta, GA (USA)

    Beech2000 Senior Member

     
  6. Gilby
    Joined: Sep 2006
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    Location: MA

    Gilby Junior Member

    Still have the ping problem? Check out the starter partially engaging at high rpm.
     
  7. StianM
    Joined: May 2006
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    Location: Norway

    StianM Senior Member

    I looked trough your pictures and I really can't see annything wrong, but I wonder what that suff in your cylinders are. Oil?
     
  8. TerryKing
    Joined: Feb 2007
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    Location: Topsham, Vermont

    TerryKing On The Water SOON

    So, I understand the main difference here was a new coil, is that right?? That's believable, given the noise / situation you described originally, and we should have suggested that possibility. Is it true this was also on 89 octane??

    Let us know how she runs with a (new, new) coil....

    The plugs look OK, but a little light / hot. A nice even light tan is the usual objective...

    Let us know what you find next!!
     
  9. Beech2000
    Joined: Jul 2006
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    Location: Atlanta, GA (USA)

    Beech2000 Senior Member

    Sensor turned out to be good.

    My dead ignition was a bad ECM from the wrong PN coil sold to me at Mercruiser dealer. Just my luck!! No returns on electrical parts at all. So the faulty ECM was the dirty culprit that left us stranded two weeks ago with many humiliation tows.

    Mercruiser thunderbolt IV ignition works well but obviously sensitive to the parts and very expensive. Replacement ECM's are $460.00 USD. Wow. Crooks!! LOL..

    Anyway, back on the water. I replaced the entire thunderbolt ignition system with performance MSD marine version components. (i.e. distributor, coil cap rotor, etc.) This turned out to be less money than buying replacement ECM and best part? “No more high RPM missing”.

    I am convinced the original coil was the source of misfire and reason for the noise at high RPM. I found traces of arcing on port valve cover. I guess this would explain my term air hammer on valve cover.

    The vessel is now noise free and runs great. Knock on wood.

    I have a complete thunder bolt IV ignition system (less ECM) that I will be posting for sale in the near future.

    Many thanks to all for your help.
     
  10. Beech2000
    Joined: Jul 2006
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    Location: Atlanta, GA (USA)

    Beech2000 Senior Member

    I posted many photos. 4 pages of them.

    I suspect it ran into #7 spark plug hole from disconnected hose from exhaust manifold water source.

    Any concern?
     
  11. Beech2000
    Joined: Jul 2006
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    Location: Atlanta, GA (USA)

    Beech2000 Senior Member

    Never would have guessed that one. Run accross this?
     
  12. TerryKing
    Joined: Feb 2007
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    Location: Topsham, Vermont

    TerryKing On The Water SOON

    OK, one more to add to our catalog of symptoms VS causes!

    Have fun out on the water....
     
  13. stonebreaker
    Joined: May 2006
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    Location: Shiloh, IL

    stonebreaker Senior Member

    OK, see how clean and white your insulators are on your plugs? You're running lean. And how some of them have little flecks that look like pepper imbedded in the insulator? You're detonating. BADLY. Not catastrophically, but those little flecks are often pieces of aluminum off the tops of the pistons. Have you tried re-jetting the carb?

    Also, looking at your plugs, it looks like the first couple of threads are sticking into the chamber, based on their color. Are you sure you're using plugs with the correct reach for those heads?
     
  14. Beech2000
    Joined: Jul 2006
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    Location: Atlanta, GA (USA)

    Beech2000 Senior Member



    No. Where do I aquire jets for Carter AFB? What jets do I buy?


    Plugs are what Mercruiser Calls for for both 5.0 litre and 5.7.
    Not sure what I would replace them with.

    Thanks Stone
     

  15. stonebreaker
    Joined: May 2006
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    Location: Shiloh, IL

    stonebreaker Senior Member

    http://store.summitracing.com/egnsearch.asp?N=700 400415 115 4294920710

    Before you start replacing jets, how much do you know about carbs?

    http://store.summitracing.com/partd...rt=SAD-SA11&N=700 4294924480 115&autoview=sku

    I'm more of a fuel injection guy, myself - the only vehicle I've ever owned with a carb was a 1980 camaro I had in high school. But if you don't have a buddy that can teach you how to tune a carb, these books can do a pretty good job - I learned most of my hotrodding from gearhead books.

    On the plugs, it looks like the threads are a little long - the first couple of threads look like they're sticking into the chamber. That may just be because of the extreme closeup pics, though.
     
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