Coil Overheating

[Argess]

I just had some trouble with my car. Once well warmed up (20 to 30 minutes) it would die. It would crank, had fuel, but spark looked weak. Once things cooled down (another 20 to 30 minutes), it would start right up.

Since it was common to all cylinders, I suspected either the coil or the ignition module... after I checked all voltages, etc. What I found was that if I cooled the coil down by holding a wet rag against it and then pouring a cup of water over the coil, it would start right up. I confirmed this three times. Just let it idle until it died, then the water treatment on the coil. Started right up each time.

As it almost confirms a bad coil, I ordered another one, but am also wondering of the module might be malfunctioning... too much dwell and overheating the coil through lengthy primary current.

Now this system is a Pertronix Ignitor with a Pertronix 1.5 ohm coil (P/N 40011). I've never seen a coil fail when hot unless there's a break in the internal coil windings that spreads apart once it gets hot. This one does check out with no breaks although the high tension side resistance measures a bit lower than spec, and a bit lower than that when hot.

A Google search reveals there does seem to be a number of people reporting a similar coil problem with Pertronix, but they all had problems early on. Mine has worked flawlessly for about 13 years.

So no real questions from me. Just wanted to share as coil issues are seldom the reason for ignition problems. Usually dist cap, rotor button, wires or plugs. Anyway, comments welcome, especially if you’ve had a similar problem before.

[HighPlainsDrifter]

Hi,
Check that the coil should be 0.6 ohms for a lot of their distributors. a coil with more resistance will create more heat.
Perry

[Tommy]

I had some self created problems with a Pertronix distributor last year and their tech support was helpful in telling me how to troubleshoot it. They also fixed it for nothing more than the cost of shipping.

[Unique427]

This applies ONLY if you have a oil filled
canister style coil mounted horizontal.

Look at the coil tower end and check that
the (+) and (-) posts are positioned
at 3 & 9 o'clock. If not, one post may not
be internally submerged in oil. This will lead
to overheating, degradation or early failure.

If mounted vertically then disregard.

[Argess]

A new coil fixed the problem.

Pertronix says their Ignitor units either work or they don't. None of this "work when cold, not when hot" stuff, however a Google Search did reveal some fellows fixed the same symptoms by replacing the Ignitor, so it can't be completely ruled out.

The old coil was manufactured back in 2010. Twelve years, but low mileage. Not all that impressive, but not all that bad either.

[RockBit]

I had a coil failure last year. The coil was an MSD Blaster II, epoxy filled, mounted vertically to the front of the cylinder head. Car would start and run fine, but occasionally while driving the engine would just turn off for a second or two, then come back on.

I replaced the coil and added a couple of nylon washers between the coil bracket and head in an effort to get some thermal isolation between the head and coil. It has worked fine ever since, but I have only put about 1,000 miles on the new coil.