Evidence of damage

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The effects of high-voltage that can't go to ground the proper way...
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Below are pictures of two coils that were ruined by high-tension voltage that had nowhere to properly go.

Mike Pardee's son cranked the engine over with the distributor cap removed, ruining the coil. Oops. The yellow arrow indicates the burnt spot. High voltage current now goes to ground through the coil body instead of through the distributor rotor terminal, so there is no spark (or a very weak spark) at the plugs.

Says Mike:
"I took a picture of the coil from my son's '94 Integra after he used the starter to bump the distributor around when the cap was off. He should have visited your site first! Anyway, by adjusting the photo and lighting I got a good picture of the "zap" spot that resulted (at the bottom of the coil, near the center). The spot is barely noticable in normal lighting."

Reader Danny supplied his own picture of the dead coil in his '96 Civic.

This coil exhibited the correct resistance when measured with a multimeter. Pushing three volts through it with a multimeter does not create the same sort of stress that pushing 20,000 volts does in regular use, so shorts like this are unlikely to show up in the shop manual-specified resistance test.

Keep in mind that high voltage can go through ANY sort of material, even the stuff you might normally think of as an insulator!

Ben Bunk has kindly provided some fairly dramatic photos, shown below. I didn't think to ask him at the time, but it would have been nice to have corresponding images of the inside of the distributor cap, which would have been the target of the devastating internal lightning strikes (and that's actually what they are) which are so evident in these pics.

	People tend to think plastic isn't electrically conductive. How wrong they are! All it takes is sufficient voltage and current. 20,000 volts as generated by a typical automotive ignition system can readily burrow its way through quite a few materials that you wouldn't think are conductive at all, such as the (ABS?) housing of your standard modern potted solid-state ignition coil. See that figure-eight, sort of rainbowy spot at the bottom of the black plastic coil housing? That's the origin of the lightning strike, where the current went to ground through the distributor cap. Once a ground is established, legitimately or otherwise, it does NOT go away. Each ignition pulse will forevermore wholly or partially ground through this unauthorized jump point, thus avoiding its intended jump point, the spark plug gap. Heat has everything to do with this. Older ignition systems that used large, cylindrical, oil-filled coils could withstand tremendous abuse. The oil acted as a very effective heat sink, something the newer light-density potted coils are not good at. Oil-filled coils could easily dissipate the energy from high-voltage pulses by heating up their own oil before those pulses had to actually arc somewhere. Sometimes "modern" isn't "better".
	Another view, another rainbow-colored short; another point of ground. This coil was arcing all over the place.
	We turn the coil just a bit to see on the other side of the steel... More arcing. Goodness.
	Even at the bottom of the coil! Not rainbow-colored here, but still... If you were tiny enough to be able to sit inside the distributor cap and witness the lightning storm as it happened, would you be hugely entertained or frightened to death? Or would you just end up being a handy point of ground? Do you really wanna know? Me neither. Ben says, "I had been driving with this fried coil for so long I got an amazing picture of how fried it can get. In comparison to the [other pictures] on the FAQ, mine looks like a nuclear blast went off in my distributor. This coil must of arc'd out in a fantastic display of electrical power because I have scorch marks the size of a silver dollar in some spots and as small as an eraser in other spots. All in all, there must be at least 5 spots where you can visibly see scorches. I thought you might want to add it to your site because it has reassured me to stick with OEM, because if OEM can keep running after as many times as it blew itself up, I'm positive I got my money's worth. Not only that, its a good comparison for anyone unsure what to look for in a fried coil because there is no question this guy is dead."

Last update: Nov20/08