Broken Spark Plug

[ratchetdu]

I noticed one engine wouldnt get up the same rpm as the other one last time out. Boat has been out 4x this year and seemed fine prior . I noticed more soot on the transom than usual when i pulled it out of the water. When starting it in the driveway, it sounded rough, and I noticed white smoke coming from the cooling pee holes as well as exhaust of port engine. Checked spark plugs, and the very first one (closest to the bow/front of engine) is missing the center electrode/ceramic around it and must have broken off somewhere in the cylinder. All others fine. Replaced with another plug, and still running rough. Ran on hose for a few minutes and still rough and smoking. Checked plug again and it seems fine, but a little wet. My friend who is a mechanic, and has been on my boat many times, thinks its a stuck injector that caused it and recommends replacing and starting with that... $150 for new one and im not 100% sure thats my issue. YDS test says operating normal. Can hear clicking during test and while motor running. He says if its stuck open during load, these stationary tests could still show fine. Ive searched here and found some info regarding stuck injectors and ecu problems being common? Not sure which I may be experiencing. Ive had the boat for 10+ years problem free with new spark plugs every year... Looking for your thoughts and assistance.

Thanks in advance as always...

 

[seadude]

You've got two motors - time to start swapping parts (if you're up to it)!

 

[Cobra Jet Steering LLC]

If you have a stuck injector your oil will overfill and be very obvious when you check it with the dipstick overfilled oil that will end up destroying your air filter element very fast as it clogs it, not allowing the engine to get enough air, thus causing the engine to run really bad and smoke. That sounds familiar!!! The concern if you have not done it yet is a compression check on the cylinder that lost the spark plug end to be sure it did not damage the piston and rings etc, when something solid is inside your cylinder bouncing around it is obviously not good, however it could have just been pushed out an exhaust valve and disappeared. Hopefully that is what happened. A bore scope would be good to inspect the top of the piston .

 

[Gym]

If I read your post correctly you believed the center electrode broke off somewhere in the cylinder? If that's true were you able to remove it from the cylinder before you ran the engine again? How old were these plugs?

Any foreign material inside a running motor will cause damage. If my assumption is correct you may likely have damaged a valve. Before tearing into the injectors and the ECU I would do a simple, no cost, compression check of all cylinders on that motor so you can compare #1 with the rest.

If I did misunderstand your post or you did remove any foreign material you can swap ECUs or injectors to try to isolate the issue. An injector can have a bad spray pattern due to carbon buildup causing a rough running motor.

 

[ratchetdu]

If you have a stuck injector your oil will overfill and be very obvious when you check it with the dipstick overfilled oil that will end up destroying your air filter element very fast as it clogs it, not allowing the engine to get enough air, thus causing the engine to run really bad and smoke. That sounds familiar!!! The concern if you have not done it yet is a compression check on the cylinder that lost the spark plug end to be sure it did not damage the piston and rings etc, when something solid is inside your cylinder bouncing around it is obviously not good, however it could have just been pushed out an exhaust valve and disappeared. Hopefully that is what happened. A bore scope would be good to inspect the top of the piston .

Ok, thanks. Oil is fine, not overfilled on dipstick and looks normal. Air filter also in perfect condition. I have not done a compression check yet, and i guess i'll start with that. Best way to do that without a tool?
Also hoping damaged end of plug got pushed out of the engine through exhaust, which seems likely from discussing with others.

Thanks again.

 

[ratchetdu]

If I read your post correctly you believed the center electrode broke off somewhere in the cylinder? If that's true were you able to remove it from the cylinder before you ran the engine again? How old were these plugs?

Any foreign material inside a running motor will cause damage. If my assumption is correct you may likely have damaged a valve. Before tearing into the injectors and the ECU I would do a simple, no cost, compression check of all cylinders on that motor so you can compare #1 with the rest.

If I did misunderstand your post or you did remove any foreign material you can swap ECUs or injectors to try to isolate the issue. An injector can have a bad spray pattern due to carbon buildup causing a rough running motor.

You read correct. Electrode broke off inside cylinder. I did not find it to remove it and hoping it got pushed out through exhaust. Only ran engine briefly in driveway and on hose for about 10 minutes, but was running for about 20-30 minutes on the water the day i noticed loss of power. Assumed something very small was stuck in cleanout as it sounded normal on the water. (Actually, the day before i did pull a piece of plastic glow stick out of the cleanout on the bad engine). The plugs are new this season and changed every year to the NGK Iridiums.

How to do a compression check at no cost? is this something i can do myself at home? I do have the YDS software as mentioned if that helps in any way?

I think i'll try swapping before i get new parts. And after the compression test...

Thanks.

 

[Cobra Jet Steering LLC]

You may be able to rent a compression tester and do some reading up on how to use it properly check with a place like N A P A auto parts etc be sure you have the throttle open to get a good reading and you will need the correct end to go down in your spark plug opening unless you have one of the type that you hold against the opening but those are usually not as effective.

 

[rkluck]

You can get a compression tester pretty cheap, maybe rent one or worst case take it someone. If you know anyone that works on engines they will have one. There is a good chance something that size in the cylinder will cause damage. You mentioned the plug you put in was wet which indicates the cylinder is not firing. I hope the compression test says you are OK.