'08 Mercruiser 4.3 runs rough - stalls and won't start in the water

[JackBronson]

Hello
2008 Chaparral with Mercruiser 4.3 TKS, serial no 1A313653

Had an issue coming home, upriver against the tide for about a 25 minute ride, engine wasn't hot or anything, boat lost power and stalled. got it started right back up and kept going, it stalled a couple more times 10 minutes later including as i was about 10' from the trailer.

Brought it home, pulled and cleaned the fuel filter which had nothing in it anyway. Ran it 3 times in the driveway and it starts right up and ran it for probably 20 minutes total. But this boat and motor is new to me, so I'm not sure how this thing is suppose to feel and run.

Brought it to lake, start pulling away from dock and there's no power and its running rough then it dies. and won't start. and we get towed.

Get it home, and it starts up and runs, and I pull and replace distributor cap and rotor they were original and cap contacts had corrosion and build up.
Now it starts and will idle, but something is still not right. the engine isn't smooth. at 1800 rpm running on the muffs its got a rough feel to it, its not a smooth acceleration as I slowly increase the throttle to that point.

Prior to all this happening I had run it for 30 minutes on the lake at various speeds and the thing was sweet. I put Sea Foam into the tank before that run. 25 gallons of fuel is from last year. to this I added another 10 fresh gallons and more Sea Foam so i don't think it's a fuel issue.

If you were me, what specifically would you check next?

Thanks in advance

 

[Rick Stephens]

Me thinks you do have a fuel problem. Seafoam is mostly a waste of money. It does not fix fuel problems. Makes you feel better maybe. First thing first is make sure you are getting fuel to the carburetor and that that fuel is clean. Pull the line off the carb, stick it in a plastic soda bottle and crank a bit... do you get plenty of fuel flow?

No? Work your way to the tank and replace filters, make sure you aren't sucking air anywhere.
Make sure the antisyphon valve isn't crudded up.
Pull the filter and dump the contents in a clear jar - clean, no water, no crud?


Yes - you got clean fuel at the carb?
Pull the screen out and make sure it is clean.
Rebuild the carb.

All of the above isn't the issue? - drain and replace the fuel. You can also try a gas can as a fuel source to make for sure and certain your fuel is the problem.

 

[achris]

First thing I would suspect is the TKS system. Make sure the diode is still good, make sure the fuse is not blown and that the temperature switch and oil pressure switch are all working as designed.

 

[JackBronson]

Chris, I checked everything except the oil pressure switch, which I gave up trying to locate. In fact, I've given up trying to fix this myself. I've been chasing this for 3 weeks now, its July 4th and I should be boating. So, tomorrow I am stopping by a highly recommended mechanic and telling him to save me from myself.
I'll update this post with the cause in case it will help someone down the road.

Thanks to you and Rick for the advice.

 

[JackBronson]

To close the loop on this, turns out it was the coil. Cold it would work fine, as it heated up to operating temperature (not 'hot' because the engine never got hot) it was malfunctioning. Next day when it was cold again it was fine, Mechanic tested it, put a new on one, and the boat runs awesome. Thank God.

 

[achris]

... Thank God.

Nah, thank your mechanic....

Happy it worked out for you. And you are the one person in a hundred who does/did have a coil problem.

Chris........

 

[Rick Stephens]

To close the loop on this, turns out it was the coil. Cold it would work fine, as it heated up to operating temperature (not 'hot' because the engine never got hot) it was malfunctioning. Next day when it was cold again it was fine, Mechanic tested it, put a new on one, and the boat runs awesome. Thank God.

Righteous! Like Chris said, almost never the coil. Happiness is.