Fouled Spark Plug

Changed out the plugs today in my 2003 Yamaha f225. I Noticed that the number 3 plug was severely fouled. The others looked good, with the number 1 looking a little dirty, if not for the number 3 being so dirty I wouldn't worry about it, but maybe its a coincidence? I run non-ethanol, with ring free and stabile.

What do you guys think caused this, and how can I correct it? Thanks.

How many hours on the plug and did any of the others on that side look even near that bad? Was it running bad? Things to check: Make sure that plug is getting fire. Have the injectors checked. If others in that side look fairly bad too then lastly, check/change thermostats.

Shawnee, there was one other plug in that same side. The number 1 cylinder, which is right above it. It was about 1/4 as dirty. I was leaning more towards a bad piston ring, or a valve seal. I'm hoping your right, and I'm wrong. I'm not sure how many hours are on the plugs.

I know on mine when they hit 100 hrs they start going down hill. 100 hrs is the service change out on these. I also had an issue with my port side thermostat hanging open a few years ago and it caused loss of power and fouled plugs. It also makes them start "making oil" and you will see oil level going higher from unburnt condensation in cylinders going to oil. That's why I mentioned that part. These engines run on the cold side even when the thermostats are working properly according to my tech. This is why it's good for them to run a WOT for a few minutes everytime out to heat them up and clean the cylinders and plugs off. At least that is what I've been told. Hopefully it's not the big stuff like rings. Good luck.

Thanks for the advice, I haven't had the boat in the water since August last year. All I have done is run it in a barrel in the driveway for 20 min at a time. Maybe that might have something to do with it. But, I,would think that all the plugs would look bad, not just one. I'm going to put it in the water today and run it, the recheck.

You could check compression and leak down test if needed. Have the injectors been cleaned

YDS software will pull any codes, testing is done with OB on and off, and time at various rpm history

How are the plug wires? Plugs getting juice?

Could be a bad plug. Does it spark?

Well I ran the boat Saturday (first time since August). I got back to the house, and pulled the brand new plugs to inspect (2 hours run time). The plugs on the port side of the engine looked like new, no discoloration. The plugs on the stbd side looked like normal slightly tan, with the number 3 plug having approximately one drop of oil on it.

Not only am I concerned with the oil on the #3 plug, but also the fact that the stbd side plugs look so much different from the port side plugs. As of right now, my plan is to do nothing and just continue to monitor. Hopefully the motor just needed to be ran up and exercised.

Do you use Yamaha Ring Free or Yamahalube? You may want to hit it with a shock treatment so to speak. Directions on bottle.

I have used ring free and stabile with non-ethanol the past 6 years. maybe a little over-kill, but oh well.

Admitting I know little about modern outboards, I'd look at the #3 plug wire and coil first. Does Yamaha run separate coils? if so you could swap the coil and wire from another cylinder on the other side to see if the problem moves. If not, compression test. All easy. Good luck...

I have never seen a center spark plug electrode like in the posted pic.

Yes, the coil packs are separate, 1 pack for 2 cylinders. So my #3 plug on the stbd side is linked to the #2 cylinder on the port side, if my memory serves me right. I'm definitely going to run a comp check to see what's going on. I don't know what else to do without spending $$$, other than continue to monitor.

Ok, sounds like you can swap coil packs and run a compression check, all free. Good luck, let us know what you find.

cutch9138":3qb77x2v said:

Yes, the coil packs are separate, 1 pack for 2 cylinders. So my #3 plug on the stbd side is linked to the #2 cylinder on the port side, if my memory serves me right. I'm definitely going to run a comp check to see what's going on. I don't know what else to do without spending $$$, other than continue to monitor.

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If that were my motor I would definitely have it checked out before I continued to run it. You could spend $$$ now....or $$$$$$$$$$ later.

I agree
coils and plug wires, etc can be tested and replaced if needed
good luck. first buy a real Yamaha manual
m2cw

Sent from my SM-G930V using Tapatalk

Thank you all for the advice, but I don't see how a coil pack or plug wire has anything to do with oil getting into the cylinder on the plug. I spoke with a highly respected technician for this area, he felt that my valve seal was acting up so he suggested that I run "mercury quickleen 2" through the fuel system at double the dose. I had around 60 gallons of fuel in the tank, so I added two bottles. I ran the boat this last weekend, putting a few hours on the motor. I checked the plugs when I got home, and the #3 had just a minute bit of oil. I am going to continue to monitor and keep you all updated.

You are right, we are arm chair mechanics and compression test should be considered

cutch9138":5myc08pn said:

Thank you all for the advice, but I don't see how a coil pack or plug wire has anything to do with oil getting into the cylinder on the plug. I spoke with a highly respected technician for this area, he felt that my valve seal was acting up so he suggested that I run "mercury quickleen 2" through the fuel system at double the dose. I had around 60 gallons of fuel in the tank, so I added two bottles. I ran the boat this last weekend, putting a few hours on the motor. I checked the plugs when I got home, and the #3 had just a minute bit of oil. I am going to continue to monitor and keep you all updated.

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There is always some degree of blow-by past the rings, a failing ignition system can fail to burn the normal deposits off the plug. You're looks a bit more than normal. Swapping coil packs, wires, etc is always a easy, free way to at least rule those out as being the point of concern. Suggest you run a compression test, if you don't have a set of quality gauges you can likely borrow them from many auto parts stores. Very simple to do on an outboard, not so much on a 427/428/454 FE motor in an early Mustang. LOL Good luck

The problem is fixed. After lots of head scratching and help from you all at classicparker, here is how I got it figured out:

Like I said in the previous posts, I continued to monitor the engines RPM and spark plugs in hopes that the problem would eventually reveal itself and it finally did.

The initial steps that I took were, compression and leakdown tests. These tests all passed, I don't remember the numbers.
I also replaced the spark plugs. I put a couple of hours on the new plugs (Max rpm 5500). I got home and checked the new plugs. the stbd bank had dirty plugs, while the port bank was super clean and barely looked used. I also looked into the cylinders and noticed that the port bank looked brand new, and the stbd bank looked dirty, just like the plugs. This made me think that my injectors were either bad or dirty, because the port bank was getting flooded with fuel.

Couple of days later I decided to run it again, this time 5100 max rpm. I got home did my normal routine, check plugs, cylinders and oil. the plugs and cylinders looked the same, but the oil had risen. So it had started to make oil as well. The fact that it was making oil, confirmed to me that the cylinders were getting flooded. (port bank) The gas from the flooded cylinders was running passed the rings and into the oil pan, thinning the oil. (stbd bank) The gas thinned oil was able to travel pass the rings on the combustion side and foul the plugs on the stbd bank.

So, I pulled my injectors, VST filter, and engine mounted fuel filter. I took my injectors and VST to local shop and had them cleaned. While they were being cleaned I decided to go ahead and change out thermostats. Low and behold the port thermostat was stuck open. I know that a stuck open thermostat will cause an engine to run cold and flood the cylinders, so this could have been my initial culprit. I got the injectors, and VST back from the shop and the shop said they were all super dirty especially, but they were all able to be cleaned.

So I reinstalled the cleaned injectors, VST, new thermostats, new fuel filter on engine, new 10 micron filter, removed all of the old gas, and changed the oil as well. I was finally able to take it out this past weekend and run it. She ran like a champ, 5800 rpm and the plugs looked great.