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Old 07-04-2020, 03:41 PM   #1
Oberfranke
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Default Question about the ignition coil

Here's my problem. After 30 minutes of driving, the car won't start. There's no spark. The ignition coil becomes very warm to hot during the starting attempts !
Even after removing the capacitor there is no spark.
I measure 6V at the right connector of the ignition coil and only 1V at the left. The ignition coil is newly installed. The breaker is ok, the ignition perfectly adjusted. There must be 6 V at both terminals?
Even before changing the ignition coil the car went out after about 20 minutes. But it could be started again cold.
What could be the problem?

Greetings from Bavaria
Gero

Last edited by Oberfranke; 07-04-2020 at 03:50 PM.
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Old 07-04-2020, 04:08 PM   #2
Patrick L.
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Default Re: Question about the ignition coil

What type of coil do you have ? There should be 6v to each terminal if the car is wired as original [which it sounds as though it is.]
There should be 6v at the open point arm and 0v when closed.
The coil should read 1.5 ohms and be either tar or epoxy filled. [ not oil]
The condenser/ capacitor could well be bad. Check for capacitance and continuity. [ I just had a no start condition and went thru 4 new 'short-proof' units before finding a good one.]
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Old 07-04-2020, 04:18 PM   #3
Werner
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Default Re: Question about the ignition coil

Gero, that sounds like a short circuit [Masseschluß Unterbrecher]. If the I-coil gets too hot, it draws too much continuous current.

Simple test: do not measure the voltage, but the current. With the breaker open, it must go to 0 amps.
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Old 07-04-2020, 06:02 PM   #4
old31
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Default Re: Question about the ignition coil

Sounds like a coil issue. Even if the coil was just installed that does not mean the coil can take the heat.

You can bench test the coil and it tests good but in the car, it can't take it.

Also purchase 2-3 condensers from A&L, they make the best ones. That could also be your issue with the condensers warming up.

Last edited by old31; 07-11-2020 at 07:59 AM.
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Old 07-04-2020, 07:19 PM   #5
chrs1961815
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Default Re: Question about the ignition coil

I think your coil is bad, even if it is new.
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Old 07-04-2020, 07:42 PM   #6
Purdy Swoft
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Default Re: Question about the ignition coil

It would be easier and less expensive to first try a new condenser . Both the coil and the condenser have the same symptoms when going out . let them cool for a while and they will usually run again for a short while
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Old 07-04-2020, 09:38 PM   #7
Tom Endy
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Default Re: Question about the ignition coil

I suspect that the high voltage windings in the coil are shorting out at high temperature. When you stop after driving the temperature under the hood goes up and the heat causes the windings to expand and if some are bare they can short out.

I had the same thing happen to me a number of years ago on a trip from L.A. to Yellow Stone. I had just installed a new high performance coil (6-volt system). When I stopped for gas north of Las Vegas the ambient temperature was 104. After I gassed up the car was difficult to start. it coughed and sputtered for he next few miles, then began running ok. Every time i stopped for gas it was the same drill. When we got to Yellow Stone it was cold there and for the next few days the car ran ok. On the way home down through hot country, same drill.

A few days after I got home the car would not start. I put the original coil back on and the car ran fine. I sent the coil back to the high performance dealer, he sent it back to the high performance manufacturer and they tested it and reported there was nothing wrong with it. I asked if they tested it with a temperature cycle. They had not. I threw the high performance coil in the trash. A Model A does not need a high performance coil.

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Old 07-05-2020, 12:26 PM   #8
Oberfranke
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Default Re: Question about the ignition coil

a nasty cause at the lower plate: The insulation of the wire was probably made with graphite grease and had become conductive by aging. This caused it to come into contact with ground. I replaced the wire. By removing the distributor cam I have to adjust the ignition next week. I hope that was the cause of my problem. The motor died after 20 minutes of driving.

Greetings from Bavaria

Gero
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Old 07-06-2020, 05:58 AM   #9
Patrick L.
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Default Re: Question about the ignition coil

That wire can/does go bad or the connector sometimes can touch the body and ground.
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Old 07-06-2020, 09:26 AM   #10
rotorwrench
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Default Re: Question about the ignition coil

The old coil testers from back in the day would start out with a warming cycle to test the coil as it would be in operation. A simple Ohms check of the primary and secondary will generally be OK when the internal coils are cold but after they heat up and expand, they will lose continuity if one strand of either coil is cracked.

An inductor or more specifically an ignition coil operating on DC current will not function well at all without the aid of a capacitor in the breaker system. The breaker makes the current into pulsating DC so that the magnetic flux in the coil core can build and collapse. The condenser rapidly stores up and utilizes the back flow generated by the collapse and induction process other wise the points would rapidly burn up. The loss of that back flow makes for a spark that is almost non-existent. Polarity is also very important to the coils function.

A person has to take care to remember to open the electrical circuit to the coil by shutting off the ignition switch any time it's turned on. If a person forgets and the points happen to be closed then the coil will heat up like any electromagnet will and this can burn the primary coil up in relatively short order.
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Old 07-06-2020, 04:42 PM   #11
Jembow
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Default Re: Question about the ignition coil

I have a similar problem. How do I check if it's condenser or coil? Should I rig up a distributor on the bench and let it sit with points shut to warm the coil?
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Old 07-06-2020, 05:53 PM   #12
rotorwrench
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Default Re: Question about the ignition coil

If a person doesn't have a good capacitor tester that can test for open, short, or leakage then the easiest way to remedy that is to replace it with a condenser that's known to function normally. To be truthful, the coil situation is about the same. A person can test with a decent quality 1.5 Ohm primary automotive coil. The old Bosch blue coil used to be decent but I don't think they are even blue anymore. NAPA/Echlin ignition products are decent over here but availability in the UK may be a no go. The A&L condensers for Model As are relatively decent quality if you can get one of those. I don't know what all is available in your neck of the woods.

As has been mentioned, make certain that the breaker circuit is in good condition. The connection between the ignition switch, condenser, and points can be compromised if in poor condition. With a movable breaker plate, the connections can easily deteriorate.

Last edited by rotorwrench; 07-06-2020 at 05:58 PM.
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