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Ignition coil failure resulting in low compressiont

Ronnie

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Here is a link to the back ground on this


but for context my port engine was rev limited to 6k rpm last weekend, when I wen to change the spark plugs I found that the second ignition coil from the front of boat had disintegrated and the top of the spark plug had broken off. Today I took a closer look.

What I did and found:
I had to remove the valve cover to get to the remaining parts of the coil and plug.

The fist thing I noticed was that the rubber seal, specifically the part around spark plug 2, was cracked.

Using clamps and compressed air I was able to clean everything out of the spark plug hole.
When I finally got the plug out there wasn’t much left of it, the sight had me concerned.

I ran a compression check and it came back at 120 psi for that cylinder, 150 psi for the other three.
I went ahead and replaced all the spark plugs in the port engine.
I also moved the second ignition coil from the other/starboard engine to the problem/port engine and the port engine seemed to run fine, I only spun them up to 6k on a hose but both engines seemed to idle at between 1,300 and 1,400 pm.
Finally I noticed that the end of the second ignition coil from the starboard engine was deteriorating.
E24C7C38-6031-4C5C-8A72-39CDC6A4BE99.jpegB7852B4E-7EBA-4690-84B2-402FD1477276.jpegC170A16D-F595-4B0F-8A0F-4DAF76A67A30.jpeg9D9D6D94-6E8D-4391-BFBB-F08DCC85836B.jpeg

What I plan to do:
Order two more ignition coils (one for each engine, I already have another coil in the mail) and two valve cover seals, Install the new parts and take it for a test ride. I will decide how or if I should address the low compression after the test ride but follow up may include selling one of my waverunners and buying a used one with the same engine that my boat has.
 
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4x15mph

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Ronnie, sorry to hear this but you have a good plan. Would you say you change the plugs every 12 months like the service manual has (12 months or 100 hours whichever comes first).
 

Ronnie

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Ronnie

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And a few more:79D9805F-E209-4749-8B71-B3C9900B7F28.jpegAB6CD570-23CE-4AD2-A0C4-E35126D55FFF.jpeg74F8A912-F956-4E3C-8BB1-9E1F941E9C65.jpeg9E9BE4A0-FFCD-4510-B59F-B9406F079CDC.jpeg
 

Ronnie

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My theory is that the valve gasket leak allowed hot oil to come into contact with the ignition coil and over many thermal cycles and uses the coil deteriorated. I will purchased two new seals. The same damage on the starboard seal would confirm my theory for me, since the same coil on that engine is showing signs of deterioration. None of the other six coils are.
 

Neutron

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I would start using dielectric grease on your coil to spark plug connections, cant hurt.
 

Gym

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Good find @Ronnie. This is the second instance of ignition boot failure I've heard of in the last few weeks on this forum. It would seem to me that periodic examination of these valve cover seals would be a good idea.
 

Ronnie

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I just ordered two seals from my local power sports shop, $43 each, compared to $32 from sports plaza but I was there so screw it. I will shop online for the next two coils. Power sports shop wanted $240 a piece, sportsplaza wants $172, the first one I bought via amazon was $120 shipped.

I normally change the plugs every other year, the plugs I just replaced we just installed before this season around March. I will be buying and using dielectric grease from now on.

Should I be really concerned with the low compression? I expect and can live with a slight loss in performance but boating with a constant fear that that the low compression cylinder will suddenly devolve in to no compression cylinder would suck.

On the bright side I just started looking for a used waverunner with the same engine, my initial budget is $8k to $10k (and wondering if I can go with a supercharged model).
 

Gym

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I don't see the connection between the failed coil & broken spark plug and low compression. Unless pieces of the spark plug dropped into the cylinder scoring the cylinder walls.
 

Ronnie

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I don't see the connection between the failed coil & broken spark plug and low compression. Unless pieces of the spark plug dropped into the cylinder scoring the cylinder walls.
That is what I think happened as well. There is almost nothing left of the center of the spark plug and there is a small chunk of metal stuck/welded to the electrode. The rest had to go somewhere, I assume scoring the cylinder walls on the way out the exhaust. I was relieved that there was any compression at all but realize that a 20% deviation from the rest of the cylinders is not good. I also have some experience / have a good idea of what it will take to “fix” this/equalize the compression, a lot. Just more to consider for decision making purposes.

The coil I ordered earlier this week was delivered today, not a bad way to end the day.
image.jpg
 
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Cobra Jet Steering LLC

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My take on this unfortunate situation. The plug had a fracture in the porcelain, maybe at the manufacturing level or from some other unknown incident, even installing a plug can crack it if the socket is not straight during installation. Or just dropping it.
In any case I believe the fracture worsened and separated the plug parts causing damage to the coil during use . The broken plug was firing and that allowed compression and fire to exit the break in the plug until it just started failing to the point that you noticed it running poorly.
 

Cobra Jet Steering LLC

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I also believe the gasket going bad on that cylinder was due to the hot gasses from the combustion chamber blowing out of the broken plug and burning up the gasket
 

Looper7

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You may also want to put some dow 4 dielectric grease on when you reinstall the plugs and coil packs. It's just a good rule of thumb for all high performance engines
 

Ronnie

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@Cobra Jet Steering LLC , Jeff I’m convinced you correctly identified what happened. My mechanic and a gear head buddy of mine said the same thing.

Today after installing a new valve cover gasket/seal on the port engine, I went to replace the spark plug and ignition coil on the second plug of the starboard (good) engine because the end of the ignition coil was deteriorating/brittle/crumbling and found the the spark plug had failed.

In the pics the 2nd spark plug is the one that just came out of the starboard (good) engine. The plug on the left is the second plug out of the port/bad engine and the plug on the right is the third plug from the port engine, I just included it to illustrate what a good plug looks like. Anyway, I ended up replacing the valve cover gasket/seal on the starboard engine as well even though there didn’t seem to be anything wrong with the one I replaced, plus I replaced the second spark plug as well.

Tomorrow I will try to conduct a compression test on the starboard engine and replace the oil and filters on both engines.9D7E3C24-8622-4C52-B20C-44B9FE4FC17A.jpeg
 

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Cobra Jet Steering LLC

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Thank you @Ronnie Your cylinder will probably be fine Although the compression level is below the others it is still above the minimum needed and I suspect if you add some Yamaha ring free plus to your fuel a couple times it may go up a bit more .
 
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