Check Engine Light on, then beeps, then engine running rough...

[bruceb58]

Nope. These were pulled right when I got home from the situation I stated in my first post. I idled on them for maybe 10 minutes... guessing? Before that though, yes, it was some WOT runs for a few minutes on a night cruise. Probably about as close as I could get to pulling them after a hard run, but not pulling them with the boat in the water.

That's why they may have a little more carbon on them.

[stifflkd]

"with 10% ethanol"

There is a well-known problem of ethanol sometimes causing such vibrations and rough running. I don't understand the technical chemistry, but the upshot is: Ethanol can cause a layer of water at the bottom of the tank and can cause debris loosening, which then clogs up the fuel system.

That only happens when the amount of water reaches a level of saturation in the ethanol which causes phase separation. The amount of water needed to do that is HUGE! If you had 10 gallons of 10% ethanol fuel left in your tank, you would need over 6 ounces of water in your tank to cause phase separation.

If you are getting that much water in your tank, you have a bad gasket around your fill cap or a faulty venting system.

I fully agree. You can actually support the case that E10 is beneficial. Prior to phase separation, any water in the fuel system will bind with the gas molecules and burn harmlessly. The amount of water is minimal and will not effect the octane. The process is the same as using dry gas back in the day.