strange spark plug problem

[wordmaster]

I have a pontoon with a 79 115 hp Johnson V4 on it. I took the boat out and was cruising along at close to top speed, motor running sweet and smooth. Suddenly it sounded like one will when it runs out of gas, spluttering and missing. I limped back to the dock, brought it home and pulled the plugs.<br /><br />I have not had the boat long and have put a total of 10 hours or so on it with the motor running fine. The plugs were two looked like they were a bit old, one looked oil fouled, and the other looked like it had been hit with a hammer.<br /><br />The one that was smashed was filled with metal particles and the electrode was dead against the tip. I looked in the cylinder and the piston was bright and clean, other pistons were black, but cleaned right up with solvent spray. The piston showed no sign of a crack or hole from hitting the spark plug.<br /><br />Go to http://www.perryelrod.com/spark/sprk.html and take a look at this plug. If anyone can be of help and tell me what is going on, I would very much appreciate it. I have seen many plugs in many different conditions, but have never seen anything like this. By the way, this plug was the same number as the other three, ie., Champion QL77JC4. My manual calls for L77J4 and I am not sure what the extra "Q" and "C" mean on these plugs. Help??<br /><br />Thank you for your answers. I don't have a compression guage, so I put new plugs in and cranked it with muffs. Removing the wire of the plug in the pictures made no difference in the running. Removing the wire from any of the other three would cause it to run worse.<br /><br />After running a few minutes, I pulled the plug in question and it was full of water. Is this a head gasket? A head gasket and a ring? Considering the way the plug was bent in, can anyone give me any ideas on what it might need and what it might cost or if it is worth fixing? BTW, it looks like carbon fouling in the pic, but it was actually metal particles in the plug.

 

[ob]

Re: strange spark plug problem

It doesn't sound good.You've got some mechanical interference in that cylinder either from a failing rod bearing or ring fragments.I suggest pulling the head cover for a better looksy.

 

[12Footer]

Re: strange spark plug problem

This plug is heavily carbon fouled,and plug 3 shows signs of water (couple beads visable.<br />My guess is a major ring failure on #3.<br />I would run a compression test, then,regardless of readings, pull the head to see what condition the cylinder walls are in.<br />If they are ok, and your compression test passed, go ahead and bolt it back together.<br />but the water present still bugs me. Perhaps a blown head gasket or exaust port plate gasket if so equipped.<br />???

 

[wordmaster]

Re: strange spark plug problem

One other thing that might help the diagnosis. When I put the new plugs in and tried to crank it, it would not crank. I looked it over, and because of a crack in the plug boot, I remembered that on the head in question, the wire from the top coil was hooked to the bottom plug and the bottom coil to the top plug. <br /><br />I re-did the wires this way, as they were originally, and the motor fired right up, giving the symptoms I put in the edit of the original message. Does this make any sense?<br /><br />If it might make a difference, the cylinder giving the problems is the one on top, on the left side as you are facing the back of the motor. The plug wires on the right side are hooked up normally, top coil to top plug.<br /><br />Thank you again for your answers. I would love to get this boat on the lake, running right. You people are great!

 

[Chinewalker]

Re: strange spark plug problem

Hi Wiz,<br /> The bottom line is, someTHING smashed the plug. There aren't supposed to be things floating around inside your motor, so it must have come from somePLACE. That being the case, you'll have to dig into the motor, starting by pulling the cylinder heads and port covers. It's possible you started with a blown head gasket, which allowed that particular cylinder to essentially be steam-cleaned of any lubricants, resulting in a broken ring/piston/etc. No easy way around it, you're in for a rebuild. How indepth the rebuild needs to be you won't know until you get it apart...<br />- Scott