What would make a coil fail? How to diagnose? MSD dizzy & Blaster 3 coil

[67resto-coupe]

My car had a really rough idle and sometimes had problems starting. Once running, exhaust smelled really rich/gassy. Found to be an ignition short and I believe I tracked it down.
The 12v wire running from the green/red ign wire to the + terminal on the coil had a loose quick splice connector.
No problem - ran a new wire with a new quick splice connector and I thought I was good.
However, upon restart, the car still has a rough/intermittent idle and seems sputtery.....albeit, much better than before.
Checked timing and we're good there. Also checked for any vacuum leaks and no leaks.

Question is, someone mentioned that the coil may be bad. How can you test it? Maybe I should check the plugs? I think this ignition short may have fouled the plugs due to poor spark.
But other than fouled plugs, how would you determine if a coil has gone bad? MSD billet ready-to-run dizzy and the Blaster 3 coil.

Thanks.

 

[tarafied1]

I had a weak coil that made my car hard to start. I thought I had a carb problem cuz it would start if I squirted starter fluid. anyway, it got to the point it would not start at all. I used my timing light to check if I had spark. I did but it was weak and I didn't know it. I kept thinking it had to be in the carb until I tested the coil. Try this:

check the resistance between the side terminals of the coil. Do this with all of the wires to the coil disconnected. You should see 0.75 to 0.81 ohm of resistance. Then check the resistance between either side terminal and the center high tension terminal. The reading should be 10,000 to 11,000 ohms. Any significant deviation from these numbers would indicate that the coil is defective.

 

[buckeyedemon]

i have an MSD blaster coil 2.

i media blasted it yesterday so i could paint it to look "stock".

i noticed some weepage of fluid around the top. it appears to be filled with a liquid dielectric. i was wondering last night how long it could take for this dielectric to leak out (especially if mounted upside down or sideways) to the point that arcing internally could occur. measuring resistance is one way to test, but i'm not sure it would reveal a problem if there was arcing occurring from one side to the other, just as an example...

 

[67resto-coupe]

meh - i'll check the plugs today and borrow a meter. before i fixed the ignition wire, there would be a splash of black sooty exhaust on my driveway.
after the fix, no more crap on my driveway and the exhaust is not as rich, but it won't idle well, nonetheless.

last time i had it like this, the plugs were fouled pretty bad. good thing my NFL team is on a bye this sunday...