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Bad coils or am I missing something?

UnorthodoxCreations

Jet Boat Junkie
Messages
202
Reaction score
193
Points
137
Location
Hanover, PA
Boat Make
Yamaha
Year
2005
Boat Model
AR
Boat Length
23
I've had my 2005 AR230 for 5 summers and have had my share of issues

Year 1, ECU went bad, sent off for repairs.
Year 2, other ECU went bad, bought a new one
Year 3, previously repaired ECU went bad, sent off for repairs along with the one I never repaired from year 2.
Year 4 was awesome. We had no issues and got to use the boat more than ever and go new places. I also now have an extra ECU just in case.

We are now on year 5. We used the boat for a day in June and had no issues. We took it to my in-laws for a long weekend and I noticed the STB engine being down 1000 rpms or so compared to the PORT at times. It wasn't all the time but occasionally. We left the boat at my in-laws and I decided I would bring fresh plugs for both engines since it was probably at least 2 years since they were changed. We don't put a lot of hours on the boat in a season but I didn't know what else to do. The tips of the old plugs looked fine but I changed them anyway. Honestly the boat seemed to run worse after changing plugs. It was down RPMS more often. I tried to diagnose with YDS software but my laptop died before I could do that and I didn't have a charger. I decided to put in the my spare ECU. I also pulled the plugs on that engine to double check my work and look for any other symptoms. After doing that the boat ran perfectly.

We have a big family vacation next week so I decided I want to double check everything at home where I have more tools, availability to get parts and resources in general versus being at my in-laws in the middle of nowhere. I also wanted to change the oil in case it was contaminated with fuel. I trailered the boat 5 hours home and Monday night my dad and I started checking it out. I started by swapping in the ECU I had pulled out. I then tested all injectors. All the injectors worked fine. None were sticking open like what happens with an ECU failure. This was somewhat of a relief but also puzzling. Something was definitely wrong but ECU/injectors were testing fine and their was no gassy smell or signs of gas in the oil. I didn't change the oil yet but the oil level is normal.

I then decided to check the coils. All the coils fire off good with spark but I was noticing some were sparking out the side of the coil body if they didn't have a plug in them. That shouldn't be the case right? I could get 3 of the 4 coils to spark through the side of the body and it was a bright spark. I'm thinking this is my issue. When running, especially under load some of the coils are sparking out the side causing RPMs to drop. I have a car with a vented hood that allows water to get in the spark plug holes when it rains. It ruins the plug boots and causes them to arc out and lose power, especially under load and this seems like a similar situation. I have new coils coming tomorrow that I'll put in. I also put together that both times I messed with the coils, it changed the running condition. When I changed the plugs at the beginning of the weekend it actually ran worse and when I changed the ECU/checked plugs it ran better.

Does it seem like I'm on the right track or am I missing something or is there something else I should be checking? I'm really hoping it's not an early ECU failure that isn't showing up with the computer because I caught it early but all signs point to the ECU being fine.
 
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