3.0 Engine issue at Idle - started out of the blue

[viper1216]

Hey guys,

Got an issue I ran into this morning. 2010 Mercruiser 3.0TKS. I was out fishing in the bay...boat was running great. Was trolling around for a while....hit the gas and cruised along the bay at speed. Got to the no wake zone at my channel, dropped the throttle and boat started running like crap. Mis-firing like crazy. Was able to goose it in and get tied up to the slip. Popped up the motor cover and at idle, the engine is jumping around like it's going to jump out of the boat and run down the street due to mis-fire. Pop it in neutral and gave it throttle and she revs right up...but back at idle skipping like crazy again. Didn't have any tools with me to really look at, and it started raining anyway, but heading back tonight after to work to take a look. I put brand new plugs (DELCO) in it at the beginning of April. Gauges were all reading fine. Not over heating and have oil pressure. Fuel was 3/4 full from last year (Marine fuel) and added in about 5 gallons of regular gas before launching it a couple of weeks ago. Had Stabil additives in gas before winter. I have had it out at least 5 other times prior to this issue and she has ran like a champ. Always starting right up. Any thoughts on what it could be? Engine has about 150 hours on it if that means anything.

Thanks!!!
Dave

 

[Bt Doctur]

manifold and elbows are 7 years old, so pull the spark plugs and check for water

 

[viper1216]

Will do. When I pull them, anything in particular that would show as water or just look for a wet plug? Will it still be wet if it has been sitting for about 4 or 5 hours, or do I need to run it up again first?

 

[Bt Doctur]

pull the plugs and see is they are wet, then leave them out and crank the motor. If theres water, you will definitely see it come out. and not risk a hydrolock

 

[viper1216]

Ok, will do. Thanks!! Just out of curiosity, if they were wet with water, wouldn't that be present during advance in throttle as well? Seems like it smooths out when I do that and only really skippy during idle

 

[Bt Doctur]

could just be a small bit of moisture fouling #4 plug and clearing itself.Whatever plug has water on it the color will be snow white because the water will vaporize the carbon deposists

 

[viper1216]

Makes sense. If that is what I discover, what is the fix for something like that? Is there gaskets at the exhaust or something that gets replaced? And something that can be done with the boat in the water? Thanks for all the info!!!

 

[viper1216]

Another quick question....when I replaced the plugs I replaced them with the ACDelco's since I think those are factory. It had NGK's in it when I replaced them. Should I pick up a set of the NGK's and put them in instead, since I'm taking the plugs out again anyway?

 

[viper1216]

Ok, so update. Went down and started it up...when it was cold, ran like a champ but started skipping again as it got warmer. Pulled the plugs and nothing really looked out of the norm. I changed them to the NGK's since I had them out anyway, but they were not wet and sign of fouling or water. I'm going to try replacing the wires. They look to be original. I had bought a set to bring with me, but they ended up being wrong. I have a 3.0 LX with the Delco ignition. Which of course local doesn't have. But the store an hour away has them, so road trip in the morning apparently.

 

[Maclin]

The distributor cap and rotor should be on your list also.

 

[Grub54891]

If it still misfires after the above suggestions, check for water in the fuel. Or the carb idle circuit got plugged up.

 

[viper1216]

Funny you mention the water in the fuel. I was wondering that as well. I do have a Racor water separator on there, but I did not change the filter this year, I did it beginning of last year. However I have a little less than a half tank of fuel and our weather the last couple of days has gone from cool/cold to really hot. Wondering if maybe some condensation may have built up. I have a drain on the bottom of the filter so will pop that open tomorrow morning and take a look at what comes out.

 

[Bt Doctur]

Thats not exactly legal for I/O`s

 

[viper1216]

Didn't realize they weren't legal, was already on there when I bought the boat. Fixed the issue, ended up being the distributer cap, Tons of corrosion on it. Changed that out as well as wires and she runs like a top now.