Coil Arcing Question

[Alumarine]

Hello again. Was getting ready to fire my 74 mercruiser 140 for the first time since re-ringing it. Removed the coil wire and cranked it for 10 seconds a number of times to build oil pressure. I could hear what sounded like an arcing sound. Turned out it was my coil arcing from the metal electrode to the top of the insulator. In the enclosed picture the arc was going from one end of the red line to the other.<br />Is this normal or does it indicate a problem with the coil? BTW I'm not just pillaging. I've been trying to help others with the really easy questions.<br />

 

[Don S]

Re: Coil Arcing Question

It could be a crack in the coil tower, look and see if you can see a crack or some carbon tracking.<br />The best thing to do is to put the coil wire in the coil and ground the other end to prevent all the arching, or disconnect the wires on the + terminal of the coil while cranking the engine.

 

[Alumarine]

Re: Coil Arcing Question

Thanks again Don. So i'm not sure now. Should it be arcing? I'll remember to ground the coil in the future.<br /><br />Hey Don, I may not know much about boats but if you ever have computer questions let me know. I also know a bit about 4runners.

 

[Dunaruna]

Re: Coil Arcing Question

The coil output will look for the easiest path to ground, if everything is in good condition, the easiest path is the tip of the spark plug. In your case (with the coil lead disconnected) it found it through imperfections in the tower. No mystery here, just electrics 101 <br /><br />Aldo

 

[Alumarine]

Re: Coil Arcing Question

Ok should I buy a new coil?

 

[Dunaruna]

Re: Coil Arcing Question

Clean it, look at it. Any cracks? If the answer is no then your good to go. If it's cracked, replace it.<br /><br />In reality, it's a sign of a strong coil and correctly operating ignition circuit.<br /><br />Aldo

 

[rodbolt]

Re: Coil Arcing Question

yep<br /> if you remove the wire from the coil end and the system is in decent shape it can generate a voltage in excess of 30Kv. it has to go someplace. always dissconnect and ground or attach a sparktester to the dist cap end of the coil wire. that being said occasinally the coil will crack or carbon track and the secondary path will be from the tower to the coil primary.

 

[Alumarine]

Re: Coil Arcing Question

Thanks guys. I'll check my coil for any cracks.

 

[flashback]

Re: Coil Arcing Question

A good simple test for the high voltage ignition system is to crank it up at night and watch it, then you will be able to see any leaks in it. (sparks jumping around). good luck