I have never fogged my efi ski boat engines, but has anyone ever run a winterization cocktail(non ethanol fuel, two stroke oil, marvel mystery oil and fuel conditioner) through their ski boat engines. I have done this for years on my mercury racing engines. What you do is disconnect the fuel supply ahead of the fuel pump mix the winterization cocktail in a separate gas can,run a hose from the fuel pump to the can and run the engine on it for several minutes. It lubricates the cylinders and the fuel injectors/fuel pump and ensures there is no ethanol in the engine fuel system.
I have been hesitant to do this with my cat PCM 6 liter because of the 02 sensors and the cats themselves. My racing engines have never had cats or 02 sensors and really don't know if this would be harmful to them. It is recommended by Mercury, Volvo marine etc