Boat engine miss

[TexaRican]

Hoping I don’t have to go join some boat repair forum lol. 2003 mercruiser 5.0 with thunderbolt V ignition. When the boat is hot like after running several all miles WOT, I’m getting what I think is a miss every few seconds or minutes at medium to high RPM. Initially it was only at really high RPM. I changed the cap and rotor which were really corroded. Wanted to do plugs but mine are so hidden behind the exhaust tanks that is beyond my capability.
Test run this afternoon started out awesome. Boat fired right up and just purred. Ran halfway up Granbury from the dam at 38mph which is the best this boat has ever done. About halfway home the miss started again. This was backed down just under 3000rpm and maybe 30mph. I’m not sure what to try next.


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[Oleman]

Sounds like a misfire of the plugs after they get hot. Be the first thing I would try. JMO. as I am not a mech...LOL

[Walker]

Sounds to my like ignition coil is breaking down when it gets hot.

[TexaRican]

Yeah, I may have wimped out on the plugs. Maybe with enough extensions and swivels I can figure it out. Would be cheaper to try that before replacing a coil - that is until I break one off in the block.


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[Tommyh]

Ford engine? Electronic ignition?

[TexaRican]

Ford engine? Electronic ignition?

Yes. Crazy that it was even running. The rotor was corroded and the points inside the cap were absolutely caked up.




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[Kingfisher789]

Fuel injection or carb?

[TexaRican]

Fuel injection or carb?

Carb


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[gfulton]

Plugs or wires?

[TexaRican]

Took another look today with the phone. I can’t get my body down there to see but I can reach all the plugs by feel and think I can get a socket on them all with a swivel extension. One looks and feels like it might be a bear. Also found out the coil is relatively cheap so with the warmer weather this week I will tackle both and see if that helps.




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[Tommyh]

Yes. Crazy that it was even running. The rotor was corroded and the points inside the cap were absolutely caked up.




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Just a heads up. The firing order should be 15426378. Youve got a chevy order written on there.

[TexaRican]

Boat engine miss

I have no idea why that was on there. The caps are marked and didn’t match that. I put the new one on exactly like the old and like stated above, ran great until it got hot. Even with the miss it is still able to get me where I want.




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[TexaRican]

Boat engine miss

Ford engine? Electronic ignition?

Not sure how I missed this but it’s a Chevy 305.


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[Rotag]

Coil or wire is going bad.


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[Tommyh]

Not sure how I missed this but it’s a Chevy 305.


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Coil or module in the distributor. Coil is easier to change out lol