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What would cause a coil to do this?

livid4dirt

livid4dirt

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No wonder i could not get my carb to tune:eek1:. What would cause the coil to burn out like that? It is a older coil, i guess i should have bought a new one when my old dizzy took a crap. Next question would this have damaged anything else in dizzy?
Thanks.........Roger
 
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Those coils need either the metal ground strap or ground wire. Because the coil is mounted in a plastic distributor cap it needs a path to ground which the strap or wire provides.
 
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Yes it did have a ground, you can't see it in photo. It had a connector on it to use one of the mounting screws for coil. I was assuming that if it was hooked up this way it should ground through the dizzy, correct?
 
On second thought, it still would not be grounded. Because the screw is going into the plastic on the cap. Why would they make them that way?
 
Ok got it now, did a part search for the ground strap. Now i see how that ties everything together...........thanks guys!
 
livid4dirt said:
Ok got it now, did a part search for the ground strap. Now i see how that ties everything together...........thanks guys!
Click to expand...

So did yours have the ground strap or wire as described?

Another thing i like to do is apply a liberal amount of die electric grease to the coil cover so to keep moisture out of the coil.
 
No it did not have the ground strap. The PO must have figured he did not need it. And I never had any problems with an HEI setup before so i never had to dig deep and find a problem until now. But i thought it was kind of odd that the connector from dizzy had three wires in it, and there were only two spades in the cap. Of course it ran w/o strap but i always had a funny little something amiss, until it burnt through and then it sounded like chitt. Thanks for the help.... good tip on the di-electric grease for the coil cover!
 
I know the problem has been solved, but a shorted tach wire(negative side of coil will blow them also. That was a new one on me.
 
I read that some where also. (Short story) My nieghbor was so tuned in to my project when i was doing my gauges he thought he would be nice and donate an older in dash Sun Tach to the build. I thought "wow that's cool" so i mounted it tied the wires together and he stops by and replys "that looks good but i don't know if it works or not" WTF? Sure enough it did not work and i unhooked it rite away. Now i still want a tach but that will have to wait awhile.
 
Not because I need one :whistle:but for future usefulness of this thread can you post the part description or number?
 
Ground Strap for HEI coil (photo)

As requested, here's a pic of the ground strap. The end with the small diameter hook goes under the coil, attached with the coil hold down screw. The blade or spade end goes in the slot between the Batt. spade and the Tach. spade on the side of Dizzy cap, thus hooking up to the three wire connector from dizzy.
 
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Did bad coil damage the ICM?

Got the new coil and ground strap installed, and a new set of plugs. Plug wires are nearly new with high heat wire covers installed on them, so i would say plug wires are good (ya i know, one should not assume anything) but it ran great before the coil problem. Fired her up and now instead of barely running (like it was with the bad coil) now it seems to be hitting on about 6 cylinders. Timing is good, firing order is correct. Could i have damaged the ICM when the coil burnt out? I tested the pick-up coil and its fine.
 
Recheck the firing order 3 times. :D You wouldn't believe how many times people accidently get it messed up. 1-8-4-3-6-5-7-2 in a clockwise rotation and make certain that the rotor is pointing to the number 1 wire when the engine is at TDC of the compression stroke.
 
Ok update on the problem: Took dizzy out went and had everything tested checked out good (ruled out that problem). Got her back up to TDC rotor was pointing at #1. Checked firing order at least twice, fired her up and now i think i got it narrowed down to some plug wires.......evidently when that coil fried it must have messed with the resistance in the plug wires somehow, or is that possible? I took the #2 wire off and did a ohm meter test and according to my Haynes manual it was past the high range tolerance as far as length and resistance goes. So it looks like tomorrow it will be all new plug wires.
 
Still not running like it should........

Been scratching my head for a couple of weeks on this one. After the shorted coil ordeal, installed new coil with proper ground strap. She ran better but not good. So re-checked TDC, purchased new wires, plugs, cap and rotor. Had ICM checked out it's fine, did all the tests for the pick-up coil with the trusty Multi-Meter that tested good. Hooked everything back up checked firing order over and over. It starts very easy and will idle but it's not getting a strong burn on all eight, #'s 2,4,6 and 8 header tubes are nice and hot, #'s 1,3 and 5 don't seem quite as warm as the even number's but they are firing somewhat, when you pull each plug wire you can tell a difference. # 7 is luke warm and when you pull that plug wire you can't tell much difference. The exhaust has a very erratic sound to it also. This motor ran great before the coil went south. With #7 acting the way it is i checked compression on #7 and it was good. So i don't know what could have happened. All of the internals are new and were broke in properly, so this is very frustating :doah:. Any help or direction would be awesome!
Thanks.........Roger
 
Have you checked for a possible vacuum leak.
Its sounds like you've got a misfire problem.
 
Yeah checked for leaks ( sprayed just about everything that would fire ) all around and no difference, new carb gasket, vacuum hoses are new. I did pick up a donor dizzy that i will try just in case i am getting some misfire from the ignition, haven't tried that yet i'm hoping this weekend depending on the weather. Would the sudden loss of ignition cause a valvetrain issue? I was not getting on it, no strange noises (rattle,clang or bang). I was driving normal to see if the tv cable was adjusted correctly. So it wasn't a high rpm event.
So that's why im having a hard time with this.
 
have you pulled the valve covers to settle your own question regarding the valvetrain issue? Not related to the actual distributor failure but maybe you've got a flat lobe on the cam and #7 is just not opening and therefor not leaking compression etc. ? Just a suggestion.
 
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