2003 Utopia 185 running on 5 cylinder

[mdauth]

I have a 2003 Utopia 185 Mercury 240 EFI. Last week the alternator belt broke while pulling the kids so I didn't notice it, just the alarm would go on time to time. when getting to the dock the alarm was staying on longer and it bogged on me. Once I got home I checked if I had water in my fuel filter so I took it off and it was clean so put it back on. Then notice the belt was broken. Today I took the boat out with the new belt and the engine was missing like running on 5 cylinder, I took the plugs out and one was black and wet so not sure what to start looking for. Bad plug, Bad coil or blocked injector? I would appreciate some feedback before I start buying parts.

Thanks, Mike

 

[Tim75]

Start with compression test, all plugs out, WOT.

Spark plug tester (or 6). Find out which plug is not firing. Swap a known good coil for the dead one. Did the bad spark condition change with the coil? If yes, replace the bad coil. If no, there are other issues. You probably need the service book, avail to d/l here.

Check the fuel pressure. (the tire valve on top of the VST.) Should be 36 psi.

Broken alternator belt? Twice? Does the alt. spin easily? Does the idler pulley spin easily? Is it worn? Is the bearing bad? Are the belt grooves rusty and chewing the belt? Is alt. or idler out of plane?

If you have water in the filter, where did it come from? You have water in the tank.
Check your fuel tank vent on the side of the boat. When you store the boat, do you store it with a full tank of gas? If not, the tank "breathes" over a 24 hour period, bringing in moist air. The water condenses on the inside of the tank.