While working on my car at night I've seen/heard the ignition coil sparking from the center HT connection to either the positive and negative terminals.

At first I thought the silicone protector boot may have been dirty and caused it to conduct but once removing it, it turns out the spark jumps from the HT center terminal THROUGH the plastic to either the + or - terminal on the coil at random.

Has this happened to anyone else before? What causes it? How to fix it?

When I get a moment I'll try and replace the coil with another I have and see if that helps. I'll also try to replace the HT lead from the coil to the distributor in case it has high resistance or something (only reason the spark would rather jump a 15mm gap over a 1.2mm spark plug gap is resistance (in the HT lead?!))

Hi diymark

It may be the coil it self leaking spark or might be cracked coil cap which going to the distributor ? check any crack on those two probably it will be the coil

thanks
Regards
sumith

Yeah its definitely the coil cap that leaks. Must be cracked as it shorts from the negative terminal to the center (high voltage terminal). You can see how the arcing has turned the edges of the cracks to like powder.

Looks like another coil it is - which sucks because this one was a brand new $50 Bosch coil with only 500Km put on it!!!

ive had that problem before! a few years ago now.

I replaced the coil and it still did it, replacing the leads did the trick!

I think somebody else posted a question about this problem not long ago.

Hmm, while tuning my carbs and doing WOT runs I could have revved the engine and the extra voltage put out by the alternator could have "over voltaged" and caused the crack - so one forum I read tells me...is this even possible - doesn't make sense to me.

I will check/adjust my voltage regulator.

EDIT: Does any one have readable (1200 wiki ones are hard to read) instructions to adjust the voltage regulator?

Now you mention it, when I tried my old (circa 1979 coil) the car barley ran (bad coil) but it did in fact still short out too.

So, I will try new leads first as they are cheaper than a coil (I was thinking of getting new ones soon anyway) - but if I have to, I'll buy a new coil in the end.

yeah i changed everything, Coil, points ballast resistor and the last thing was the leads and it fixed the problem, give it a go and let me know.

Ok, a new rotor, cap and leads later the car worked great and idled higher too (old leads were pretty bad).

However, the coil constantly sparked the to (-) terminal with a faint spark and sparked occasionally to the (+) terminal with a big thick spark.

Then all of a sudden the engine died and as it turned over slowing down it would spark to the (+) terminal from the HT terminal with huge full power sparks.

I put a DMM on the coil and I get 13.8K and 1.3

So now looks like I need a new coil - anyone have any ideas of a "performance" one to use?

Hi diymark

I use LUCAS Cold color barrel type ignition coil, no matter it is now about 5 yrs no problem, and also i have heard LUCAS cold color coil is used in high performance cars and rallying too, but i don't know exactly.

the voltage ratio is bit high than stock coil on this as i remember

thanks
Regards
sumith

i have a bosch GT40 coil and it works great ,and they arent too bad on price ,mine is the GT40R which is the resistor type

and plus it says GT40R so its sounds fast!!