What would cause a coil to fail?

bkedman · 03-23-2010, 11:24 AM

My buddy at work has an '07 I/O 4.3 190HP (carb) that every 2nd or 3rd trip the coil is burnt. Any clues what would cause so many coil failures?

TIA

MattPark · 03-23-2010, 11:39 AM

A voltage spike would be my first guess.

Maybe I should ask you what you mean by "burned"

bkedman · 03-23-2010, 12:18 PM

It arcs between terminals and as soon as it travels like that the coil is dead and the motor won't start. No juice.

What would cause a voltage spike?

Orca · 03-23-2010, 12:20 PM

Overvoltage (alternator regulator out, or incorrect coil used)
Heat
Ignition left on without engine running

And if engine does not run well:
Plug wire resistance too high, or wire broken
Bad (cracked) distributor cap

Quote:

Originally Posted by bkedman

It arcs between terminals and as soon as it travels like that the coil is dead and the motor won't start. No juice.

What would cause a voltage spike?

Hmm, coil terminals are like 2 inches apart. One source says 30kV/cm for breakdown in air to form an arc, so how about someting like 150kV to arc across the terminals. The primary side (those terminals) should be run by 12V, so no way I can see that they should be arcing. Maybe secondary side (coil wire) to one of the terminals? Now that could be fatal to the primary, but even then, where is the 150kV coming from to arc from the tower to one of the terminals? Something is very wrong!

Califbill · 03-23-2010, 09:29 PM

Wrong coil. One with out an internal resistor or the ballast resistor or resistance wire is bypassed. Check to see iif it is 12+ volts at the power terminal when the engine is running. If external resistor, should be about 9V.

Fishnchips · 03-24-2010, 05:52 AM

Most likely left on too long without engine running or ballast resister is not present.

bkedman · 03-24-2010, 07:34 AM

Quote:

Originally Posted by Fishnchips

Most likely left on too long without engine running or ballast resister is not present.

Thanks guys for all the input. He's really frustrated and doesn't trust his boat anymore since this is the 3rd coil in less than a year.

What is a ballast resister and where would it be found?

Califbill · 03-24-2010, 10:11 AM

It will either be a ceramic thing about 3" long with a wire connector on each end, normally on top the engine. Or a wire, forget which color, with a tag on it saying fusible link, or resistor wire.

Orca · 03-24-2010, 11:40 AM

I would get the manual to verify what coil voltage the engine desires. It is newer, and I would think would have electronic ignition and 12V coil, but a check of the wiring diagram would be good. If it indeed has a resistor wire or ballast, then you want to make sure it is pressent and the voltage at the coil is the 8 - 9V, rather than 12 - 14V.

Here's a ballast resistor - http://www.amazon.com/Mallory-700-Pe.../dp/B000BWE37I .