engine runs great, dies, restarts after 15 min, dies

[roadnsky]

DITTO

I'm pleased to report that with my electronic ignition, substandard Flamethrower® coil protected by a 0.885Ω ballast resistor and 14.2V alternator output I have enjoyed trouble free operation for 5 years...

I have the same setup as Neil and have 7 years of trouble free now.

[joe_db]

Add:
35 amp 13.8 volt alternators replaced with bigger alternators and different voltage regulator settings. System voltages now are frequently in the 14.2-14.8 volt range.

Bad original wiring with a lot of voltage drop replaced (i.e. happy accident of 30 feet of thin alternator wire was long coil life )

These coils no longer used in current cars. I cannot prove it, but I suspect a lot of them are now made by second and third tier manufacturers. Our original coil lasted for 15 years of heavy use. A follow-on effect is that the local parts guy doesn't know 4 ohms from 3 Stooges. Our local Western Auto is an exception, if you start asking for coils that don't need a resistor the parts guy says "Atomic 4, right"

So Bryan, the short answer is that often with a switch to electronic ignition, you start frying coils...they should run for 45-60 minutes after they cool down, but once they are fried, they are unreliable even for testing.

What was determined was some external resistance is needed in front of the coil, unless you get the Moyer coil now offered in the store which has enough internal resistance to handle the issues discussed in all those threads. What I think we all realized was the extended dwell from an instant on/off electronic ignition was allowing the voltage in the coil to build up in between sparks and short itself out...with points, this was not an issue.

It has been a while, so if I screwed something up in my short story analysis, I am sure I'll get corrected.

[sastanley]

Neil, "Saturation" was the word I was looking for when I was typing but couldn't come up with it, thanks.

[ndutton]

Neil, "Saturation" was the word I was looking for when I was typing but couldn't come up with it, thanks.

It's a team effort pal. Seems I'm still a little sensitive when voltage enters the discussion. Voltage has it's place in the mix though.

[sastanley]

There might have been a couple beers involved on a Friday night in the garage while trying to be an armchair quarterback!

[Bryan Howell]

Shawn, thanks for the explanation. I was a bit puzzled why the electronic ignition would cause coil failures. I "kind of" understand your explanation.

[JOHN COOKSON]

I was a bit puzzled why the electronic ignition would cause coil failures. I "kind of" understand your explanation.

I'll attempt to explain it in slightly different words.
If to many amps flow throughout the coil primary winding over a period of time the coil will over heat and become damaged. The period of time is fixed with an electronic ignition and is ~ two times the period of time that current flows through the primary winding when points are used. So if one uses a coil designed for points the coil might over heat when an electronic ignition is used.
Amps (current flow) are directly proportional to volts and inversely proportional to resistance. If you have a coil with insufficient internal resistance you can add a reister before the coil to boost the total primary resistance or buy a coil that has the proper resistance. This will reduce the amp flow over the "period of time".
Since amps are directly proportional to volts it is important to check the voltage output of the alternator and put that into the equation also. Said another way even with the correct resistance if the voltage to the coil is to high the coil will burn out anyway.
Discussion: There is a balance here. Not enough amps through the coil and the spark plugs will fire weakly or not at all. To many amps through the coil and the coil will become heat damaged. If you follow the advice given you will have many hours of happy motoring.
Coil heat damage is cumulative. The best thing to do with a heat damaged coil is deep six it. If you need a spare buy a new one. IMO an unreliable spare is no spare at all.

TRUE GRIT

[ndutton]

I have the same setup as Neil and have 7 years of trouble free now.

Point of mathematical accuracy: are you saying you had a ballast resistor in 2009, two years before we slogged through the coil studies??

[roadnsky]

Point of mathematical accuracy: are you saying you had a ballast resistor in 2009, two years before we slogged through the coil studies??

Nope, bought the coil in '09 but copied your setup () in 2012.
So, the coil is 7'ish but the resistor "setup" is a bit over 4 years.

[joe_db]

I have always been slightly frustrated that neither Moyer nor Indigo have investigated the more advanced versions of the ignitions they source that DO reduce dwell at lower RPMs.

[ndutton]

I have always been slightly frustrated that neither Moyer nor Indigo have investigated the more advanced versions of the ignitions they source that DO reduce dwell at lower RPMs.

Why not try it yourself? For the late model Delco distributor the Pertronix P/N is 91146A. For a fair test you should use their recommended Flamethrower® coil too.

[joe_db]

I may do that, but I also may have another ignition project in mind. I'll post that in a separate thread.

Why not try it yourself? For the late model Delco distributor the Pertronix P/N is 91146A. For a fair test you should use their recommended Flamethrower® coil too.