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I am concerned...motor issue?

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Old 07-09-2006, 11:39 PM
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Default I am concerned...motor issue?

I have a 496HO. When I start it for first time in a 24 hour period, all is fine. However, when I run her and retart her within an hour of the last run, I get this black smudge from my exhaust pipes (I have rubber flaps to prevent water from backflowing in if this matters). It is a bit hard to explain - will get a pic however looks like a combination of oil and soot that just sits on the top of the water. At times, it is excessive, making a line about 1" wide across the entire width of the back of my boat.

Any ideas?

Last edited by Ca$hed Out; 07-09-2006 at 11:43 PM.
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Old 07-09-2006, 11:43 PM
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Default Re: I am concerned...motor issue?

merc calls this trailering effect it is common on boats with intergrated swim platforms they do have a current reprogram bulleten on it but still does it but the update does help a little
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Old 07-10-2006, 12:53 AM
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Default Re: I am concerned...motor issue?

Shawn, do you have Captain's Call or Corsa Switchable exhaust? Sounds like the bit of water that sits in the tubes after you run for a bit dissolves some of the soot inside the exhaust, and oozes it out when you are bobbing.

Get ahold of a Merc Dealer and run your ECU's serial number through the system. There have been about 5600 different reprograms for the 496s. I had mine reprogrammed via a ECU swapout, and mine leaned out a bit and gained a little fuel economy; much less transom soot as well.
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Old 07-10-2006, 08:20 AM
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Default Re: I am concerned...motor issue?

Newer Merc's like the 496HO run quite rich in their stock form. There is a bulletin on this soot, and I think all they do is reprogram the ECM to eliminate it. My Baja with the 496 would do the same thing - after a day out, my transom would be covered in soot.
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Old 07-10-2006, 09:57 AM
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Default Re: I am concerned...motor issue?

More then likely they have to much startup enrichment in the higher coolant temperture tables. Common on cammed GM cars and trucks too, I usually adress that in the warm startup enrichment tables by taking away some fuel. I am sure they adressing it in the same way with the new flash.
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Old 07-10-2006, 07:34 PM
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Wink Re: I am concerned...motor issue?

Another thing to keep in mind here. Stock 496Mag's and HO's are setup to run on 87 octane fuel. If you run them on 91 octane or higher you are actually slowing down the burn and losing a little power which will increase the soot you are describing and cost you some power.

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