Coil failure ?

Conaway2

Conaway2

Well-known member
As I was driving my ‘31 Model A home from the local gas station yesterday, the engine suddenly died. A little roadside diagnostic work suggested an ignition issue - confirmed later after being towed home.

Points and condenser were replaced several months ago, engine timing is right on. Although there is absolutely no spark, the ammeter shows deflection as the starter cranks the engine over - from the points opening and closing.

I suspect the coil, although I guess the condenser could be part of the issue as well - it’s an original style one installed in the original distributor.

The coil is an original one - almost 90 years old. I‘Ve never had a coil failure on this car in the 50 years I have owned it.

Has anyone else experienced a sudden coil failure ?? Thoughts ??

Thanks - Jim
 
Well, it’s obvious the coil is trying to work, because your amp meters moving. Have you checked for spark at the coil wire to ground. Coils do fail, but not as often as people think.
 
yes - I pulled the high voltage wire out of the dist cap and held it close to one of the head nuts while cranking the engine with the ignition switch on - absolutely no spark. Also - after the first few seconds of cranking, the ammeter stops deflecting ‘normally’ each time the points open and close and starts swinging back and forth - showing discharge and charge- as if the coil is generating a back voltage - never seen this before. I suspect the coil has an internal short.
 
Maybe the cutout opened up disconnecting the generator from the battery, the generator voltage goes high because it is not regulated by the battery and the excessive voltage overheats the coil and damages the coil windings. Ed
 
Check the coil for carbon tracks . Carbon tracks will short out the coil if they make it to the metal part of the coil . If a carbon track is found , it usually can be scraped off with a pocket knife and all should be well .
 
I have recently had a coil failure such as you describe. My Model A would run fine for 10 minutes or so, then it would start missing and barely run. Once it cooled down completely, it would run again for about 10 minutes.

After replacing the coil, I am back in business.
 
Might check the resistance in the primary and secondary windings. Seems like the secondary winding may be the issue. Unless there is a hard failure, coil troubleshooting can be challenging. The number of coils changed is much more than the number of actual failed coils. Let us know what you discover.
 
Ed in Maine said:
Maybe the cutout opened up disconnecting the generator from the battery, the generator voltage goes high because it is not regulated by the battery and the excessive voltage overheats the coil and damages the coil windings. Ed
Click to expand...

1. If the cutout opens, how does generator voltage get to the coil? 2. Isn't generator voltage regulated by the position of the third brush, not the battery?
 
Last edited:
Voltage depends on the volt of the battery that is used . the generator charges in amps and the amount of amps that the generator charges is controlled by the adjustable third brush in the generator . To increase the amount that the generator charges push down on the third brush . to decrease charge , raise the third brush .
 
The condenser would be the first suspect on my list Those original style condensers are real cheaply made inside take one apart. After taking one apart and seeing how the connections are made and what they are made of I am using only the more expensive short proof condensers . B0B
 
Mine failed on a rural road in Nevada, 50 miles from nearest house. I let it cool turned it over and drove home. Bought a new coil and have been carrying it around in the car for 2 years but the old one is still working. Old coils are oil cooled and sometimes short-out when pointing down. Good luck
 
I've had coil failure in cars, but it's rare. My A was running great this summer but started missing and would barely run. Stalled in the driveway so I pushed it in the garage since it would not start again. Swapped the coil out but still nothing. It had a "made in USA" condenser that I had swapped out two years ago from my Dad's stash, so I didn't think it was the culprit, but changed it with a short-proof one from Snyders and engine started right up.
 
Did you replace the condenser for a reason? I would look at the work you did recently before changing out a part that has been trouble free for 50 years. Those old coils are known to be very reliable.



On a side note, I recently acquired 2 untested original coils. Put them both on the car, both made a nice strong blue spark. Gave one a coat of paint, put it on the car and I swear it runs better than the 30 year old oil filled coil it replaced.
 
dansluck said:
Mine failed on a rural road in Nevada, 50 miles from nearest house. I let it cool turned it over and drove home. Bought a new coil and have been carrying it around in the car for 2 years but the old one is still working. Old coils are oil cooled and sometimes short-out when pointing down. Good luck
Click to expand...

Modern replacements are oil or epoxy type material filled. The oil types often can be shaken to hear sloshing , and the windings may not get completely covered. . Supposedly Ford developed a molten asphalt based insulating fluid called Hydrolene that would solidify into a paste that was used in some later Model T coils and could have been continued on in later years' coils. Some owners like to install the modern oil types with the terminals up for better coverage.
Same experience as in post 14.
 
I purchased a NOS Delco coil for my 50 olds it quit on me after a short while,when the engine rpm went up the engine would start to die,then it left me on the side of the road.The condensers are all original style for the most part,Brattons sells an excellent one.
 
Update - new coil and condenser installed today, although both removed parts tested OK with my DVM. I have good spark now, and the timing is right on the mark, but the car will still not start. I’m puzzled, as there is plenty of fuel flow to the carburetor. tomorrow, I plan to take the carb off and check it out. The car died suddenly after I had just filled the gas tank to the top and was driving home at 40 mph or so. I would appreciate any bright ideas, as I am puzzled !
 
Sudden death would usually turn me towards the ignition system. However, gas flow to the carb doesn’t always equate to gas flow out of the carb. Crank it and see if the plugs get wet?
 
You must log in or register to reply here.
Back
Top