no_radio

My '74 Corvette has ruined three coils in the 3000 or so miles I've driven it since I restored/modified it. The symptoms start with a hard start condition, and miss at part throttle, then I will see the oil leaking from the coil housing through the high-voltage wire plug. This has happened with one brand new Pertonix coil and two brand new Accel Super Coils. At least once I have felt the coil and it was pretty hot even though the engine was off and had cooled down. I am preparing to double check all the wiring and grounds, but I was wondering if anyone else had solved this problem so I could have a direction to follow.
It is the original 105K mile distributor, and has had two or three sets of points and a Pertronix Ignitor installed during the various times the coil failed. I am planning to install an MSD billet distributor and 6AL box, but want to solve this problem first.
Some possible problems I've thought of are poor ground to the chassis, poor ground within the distributor, poor connection at the starter, incorrectly wired at the starter, or maybe a bad starting switch at the base of the column.
Thanks in advance,
Jeff

rainman69

First thoughts: Pertronix units haven't been doing too well in Corvettes (from some board memeber's experiences). Also, the voltage going across the primary side of the coil is important. Should it be 12V or less (with a ballast resistor)?

Next, check the wiring to the coil. (+) should eventually go to the start/run side of the ignition switch. (-) should go to the points (I think...this is where I get mixed up, these two).

I'm running a 6AL, billet dsitributor (tach drive), and Blaster 2 coil. No problems with 6000+ miles so far. Well, except maybe for that ionization of the air around my spark plug boots, and the every once in a while arc from the secondary side through 3/4" of air to the primary side of the coil. (I think I need the tall tower coil...) :smash:

Jvette73

I fried one of my coils by leaving the key on overnight without the engine running. The coil overheated and was leaking out oil. My ignorance did not effect the ignitor though. Somehow it survived.

mrvette

OK, here is what' happening, the points or any other igniter circuit take the negative side of the coill to ground for a few degrees of rotation, positive being connected to what we call 12 volts....SO with points open and no current drawn, we measure 12 volts on both sides of the coil....NOW if we ground the coil negative wire....shorting out the points, like they were closed.....the + terminal o f the coil better see about 6-9 volts and not over....
IF it's over....you are in trouble,....reason is that there are TWO wires in fact going to the + side of the coil, regardless of how it looks, they may be picked up in the harness somehow....anyway, the RUN wire is in fact steel and is a resistor wire, saves a component.....and it drops voltage to the coil as higher currents are drawn, after the points are closed for about 1/2 the normal time....that allows the coil to saturate magnetically without shoving currents too high for the coil....NOW having said that about the RUN circuit...remember I said there are in fact two wires going there, ONE, goes to the battery nearly directly but in ONLY energised with the starter, either through the 'other' unused sometimes small connector on the starter solenoid...OR picked up through the ignition switch directly in the START mode ONLY.....NOW that supplies a very high spark energy under diminished cranking conditions....IE about 11 volts or so available anywhere....so the sparts are HOT for starting...better ignition....
but RUNNING it that way will fry the coil....

forget about any other troubles....

unless by chance your DWELL is way in hell over tight....in other words points are barely opening....I presume you checked that....

GENE

Garys '68

You've probably left out the ballast resistor resulting in a full 12V with the key in run (check coil + terminal with voltmeter with ingition in run). Add an external ballast resistor.
Or you've wired the bypass wire incorrectly from the starter solenoid to a 12V supply (should supply 12 volts only when cranking).
My $0.02
Gary

PRNDL

But if he has a Pertronix installed it should be ok to run fulltime 12 volts, right? I thought fulltime 12 volts fried the points, not the coil. One easy thing I would check first: Based on what you said about the coil being hot, I would make sure it is not getting current when your car is turned off. Sounds strange, but it could be wired that way - and it would be like you left your key in the "on" position which would fry your coil, as Jvette73 mentioned above. MJ


[Modified by MNJack, 11:14 PM 11/29/2001]

no_radio

I should mention that I removed the Pertronix because I thought it had caused the first coil failure, in hindsight it probably didn't...
I think the first thing I will check is that I have the two wires on the solenoid on the correct terminals...If they are reversed it would cause me to be running full 12-volts during normal engine operation, and probably cause the burnt up coils.
I have considered the possibility that the coil is receiving voltage even after the engine is shut off, but that puzzles me. I used to hot-wore my '71 Javelin, and that is how you do it, you run a 12-volt wire to the coil and you can't shut the engine off with the ignition. Essentially you bypass the whole ignition switch. So I don't understand how the coil could be seeing voltage when not running and still be able to start and shutoff with the ignition key...BUT, I'm not ruling it out.
Thanks for the replies, if anyone else has something to add I'd love to hear it!
Jeff