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Johnson J25 ELCTD keeps burning out top coil

C

c-dubb

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Does anyone have an idea as to why this motor may be burning out the top coil only? I purchased this motor a few years ago and within a week the top coil went out. I replaced it with the CDI replacement coil and it went out after about a month. I then replaced it with the Sierra replacement coil which lasted about 1-2 months. I then replaced it again with the CDI coil and it lasted about a year and now it is out again. Any help would be appreciated.
 
Ground wire and coil body must be completely grounded with star lock washers, brother. I use anti seize also. Use dielectric grease in plug/boots. Should last 20 years.
 
Replaced the bad coil and still couldn't get it started. Tested compression and got 0 psi on top cylinder, so I pulled the head and found a blown head gasket. I'm thinking that this engine was overheating the whole time and the coils were getting damaged from the heat. I pulled the lower unit to inspect the water pump and it all looked good to me but I ordered a new water pump (housing and all) to go with the new head gasket. The thermostat is not yet a year old and I will be testing it for proper operation while it is torn apart. I was getting a good stream of water from the tell tale, but not right away. It seemed as if I wouldn't get a stream until the thermostat opened.

Are there any other things that I should be looking at while it is torn apart?
 
How could it have been eating the top coil? Overheating? Unlikely. The head gasket now, did it burn across to the water jacket? This would have been a slower process and you would have noticed loss of power and disruption of water flow ask bubbles get into the water. This, of course would cause hot and cooler spots in the powerhead, but not likely hot enough to score the affected cylinder. I have run into this before. 0 compression is hard to imagine in this scenario. For me, it just doesn't add up very well. We can plead to other techs here to see what they think.
 
timguy said:
How could it have been eating the top coil? Overheating? Unlikely. The head gasket now, did it burn across to the water jacket? This would have been a slower process and you would have noticed loss of power and disruption of water flow ask bubbles get into the water. This, of course would cause hot and cooler spots in the powerhead, but not likely hot enough to score the affected cylinder. I have run into this before. 0 compression is hard to imagine in this scenario. For me, it just doesn't add up very well. We can plead to other techs here to see what they think.
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Both coils had been oozing a clearish yellow sticky film since before i purchased the boat. I always just assumed maybe age was a factor until the top one kept going out. The metal ring on the head gasket did burn across to the water jacket and coincidentally in the same area as the coils are mounted.
 
Coils can take lots of heat. I have seen them partially melted where they contact the head. The motors got so hot, they are toasted......scored piston. I have cleaned up and reused the coils. Worse situation is when they get cracked and ground out. You can check them with an ohm meter. CDI, through this marineengine site, has a great diagnostics manual, free for us to use. That's why I purchase CDI components. I really can't put a finger on the cause of your coil failure yet. Any other techs out there?
 
My experience with this particular coil, however, has been if its hot enough to damage the coil, it will also overheat the piston and cylinders to the point of destruction. If this has been a continuous overheating, over the course of years (according to the outboard owner/operator)........sorry, but my feeling is that the powerhead itself is damaged quite severely.
I, just last year, rebuilt a Merc 25 2 stroke that overheated to the point of almost catching fire. It was actually froze up when presented to me. The coils were badly melted on the surface of contact. I cleaned them up and reused them.........cutting away the melted plastic coating. The pontoon is still running great, I gave him a full, unconditional one year warranty on the rebuild.
 
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Update: Installed new water pump kit and head gasket. I now have 120 psi on both cylinders and it fires up immediately, hardly having to turn the key at all. It has never started and idled so good since I’ve had it. I’m not sure about the water flow from the tell tale now as I don’t have near the pressure coming out as I did with the old water pump, but it is still a steady stream. I will likely pull the lower unit back off. Old head gasket was very deteriorated and it seems as if it had been causing the side of the head with the coils on it to get hotter than the other side judging by the signs.
 
Excellent job, could be that the compression leaking in at certain points before, added some pressure in a way that forced more water out the pee hole. What do you think of that theory? You can tell that it is not too hot by feeling the cyl. head area and count to three or so without burning your hand.
 
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Just ran it in the lake and still not much water from tell tale, almost no water coming out at idle one time but plenty coming out while running WOT. Wondering if I’m losing pressure somewhere, maybe the supply tube at the power head? Should it have had an O-ring or something on it?
 
Idleing in a drum with water barely dribbling out of the tale tell it will be hot enough that I can hold a finger on it for a few seconds. I am gonna pull the lower unit back off in a little while just to check things out.
 
Pulled lower unit and found that the water pump housing wasn’t sealed very well and was in fact losing pressure. Put everything back together and she is pumping water like a boss.

Summary:
It appears that the head gasket was deteriorated so badly that it was causing uneven heating of the head and cylinder walls. This heat seemed to be concentrated to the area where the coils were mounted causing heat related damage to the coils. It also was a contributor to the hard starting and poor idling until it got bad enough to lose nearly all compression on the top cylinder.
 
Great job. Maybe now you can get some fishin' done. I'm going out today with my 1956 5.5 hp I intend to outfish my wife, but that NEVER happens.
 
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