Mercruiser 470, Help me understand this solution

[a1nowell]

I have an '84, 470 pushing a 24' JC Tritoon. Over the last couple of weeks I have been doing my Spring maintenance, oil & filter change, lube all the grease fitting, new fuel/water filter etc. I also changed my plugs, wires, dist/cap & rotor. (Petronics ignition) The engine ran like a top on the muffs and 2 short trips in the water. This past weekend we went on our annual mens retreat at Lake livingston, Texas. After launching the boat and now out on our first long boat outing, the engine started to miss pretty bad after about 10 minutes into the trip. I decided to go back to the dock and was able to make it but the engine was missing pretty bad. After docking and letting the engine cool (it never got over 160 degrees) I check to make sure all my wires were good and tight, checked inline filter good & clean etc. After about an hour, fired the engine up again no miss, running smooth, took her out again and after about 10 minutes, same miss and rough running. I repeated this event with the same results several times. I spoke with a friend who is a shade tree mechanic, told him all this and what I had replaced and he suggested my coil could be going bad. Seeing how I had replaced everything else electronic I thought what the heck, there is a NAPA 20 minutes away so I got a new coil and installed it, problem solved, we spent the rest of the weekend putting more than 12 hours on the boat with nary a miss. I would think a coil would work or not work. How does a coil screw up like this, do I really have my problem solved?

I would appreciate any thoughts on this.

Thanks,

Larry

 

[Bondo]

Re: Mercruiser 470, Help me understand this solution

How does a coil screw up like this, do I really have my problem solved?

Ayuh,.... Donno if ya solved the problem or not, but heat does funny things to electrical parts,...

What voltage ya feedin' the coil,..??

While readin' yer story, I was thinkin' fuel tank vent restriction...

You usually find the answer, by lookin' at the Time of the Issue,...
Is there spark,..??
Is there fuel,..??

 

[mpdive]

Re: Mercruiser 470, Help me understand this solution

Coils can definately deteriorate over time. It can sometimes be caused by improper gapped plugs, bad wires, bad rotor, etc. This can cause the premature failing of the coil insulators. Glad your up and running. Dont know much about your engine, but is an auto coil ok to use? Don or Bondo would know this. Not sure if it needed to be marine.

 

[stonyloam]

Re: Mercruiser 470, Help me understand this solution

I would think a coil would work or not work. How does a coil screw up like this, do I really have my problem solved?

Sometimes a coil will develop a crack or just be dirty or pitted from arching due to poor contact with the center wire. The high voltage spark is always looking for the path of least resistance to ground which is not always through the plug wires. If you still have the old coil, take a real close look at the top to see if there is any evidence of pitting or burning or "tracks" from the spark. Another problem could be the wire + - terminals, high resistance there could reduce the coil deficiency and produce a weak spark.

Maybe, time will tell

 

[a1nowell]

Re: Mercruiser 470, Help me understand this solution

Thanks to everyone for the rapid replies. What I bought was an automotive coil that operates with an external resistor. I need to investigate what kind of electronic ignition I have. Looking on line I saw there were several coils throwing different voltages depending on the type of ignition you have.

Thanks for the imput.

Larry

 

[Oldrod 47]

Re: Mercruiser 470, Help me understand this solution

If you are runnning Pertronix ignition system go to their web site or call their tech. line and ask what their recommendations are for a coil. I am running a Pertronix II and it reguires a 12 v. source, no resistor for the coil. The best place to go for information is the mfg

Most part counter guys now days can't find anything that is not in the computer. ( Go to any big box auto parts store, tell them you need a rotor for a small block chevy- what year and model parts guy asked- answered 40 Ford-parts guy " its not in computer" It happened)