200HPDI carbon build-up

[tonynorie]

The motor is a 2001 200hpdi and the problem of carbon build up has been going on for a long while. After only 5 or 6 hours of running the plugs have wet buildup. Here's what I've done so far:

Replaced water/fuel separator, VST filter, strainer filter, paper filter. Cleaned O2 sensor. Thorough decarb with Seafoam. Replaced plugs.

I run E-10 and have always used Ringfree at the recommended dilution rate.

The motor seems to be running well but I'm concerned about the carbon doing long term damage and I want to get it resolved. Is it time to take it to a mechanic and have it diagnosed, or is there another approach that I can take on myself?

Thank you!

Tony

[robert graham]

Maybe motor is running too cool, never reaching normal operating temperature, causing a continual rich mixture.....Check thermostats.

[tonynorie]

Thanks Robert for your suggestion. I neglected to mention that I replaced the thermostats about 100 hours ago. Do you think I should pull and test them with that little bit of service on them?

Tony

[robert graham]

Well it wouldn't hurt to double-check the thermostats/engine running temperature, because that's an item that will cause a rich, wet, carbon-fouling condition. Does your motor run well at wide open throttle, say 5500RPM's? How much smoke? Good Luck!

[tonynorie]

Yes, it seems to run good throughout the range, up to and including 5500 rpm. A while back I went to a 21p prop and that size on the Pathfinder 2200 seems to get the desired rpm's. There is what I consider to be excessive smoke at startup, especially after an extended run at higher rpm, but otherwise it's ok.

[bumperfood]

Have you tried using a different brand of oil?

[rodbolt17]

have you actually TESTED O2 sensor output vltage?
have you checked high pressure fuel system?
what color are the ign coil primary connectors?
what plugs are you using?

[tonynorie]

From a previous post I know that the plugs are the correct one for my motor (can't actually check coil wire color as I'm not where the boat is). No, I haven't checked high pressure fuel system. Is that something a DIY'er can do himself and does it require special tools? And although I cleaned the O2 Sensor I did not check voltage and will try to find the procedure on doing that. Thank you!