Pertronix fails after 5 minutes of running.

I have identical 9N's that I have been posting about recently. One I work with a couple days a week and have had a pertronix unit in it for years without a problem even with the regular 12 volt square can coil and solid copper plug wires that are supposed to be a no no.
Recently I finally put rear tires on my other one and even though I have it wired exactly like the one I use all the time I got no spark. I called Pertronix and they said because it sat for a couple years "who knows what could have happened Mitchell said" So I bought another module put it in and now it runs but only for about 5 minutes or so and then quits. If I let it set for a half hour or so it will run another 5 minutes and then quit again.

Can't get alot of work done in 5 minutes LOL

Swap the coils and resistor between them My vote is a bad coil. Jim

(quoted from post at 14:21:11 11/08/21) Swap the coils and resistor between them My vote is a bad coil. Jim

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I have another coil in the garage I can try. The one on it has .003 resistance and the other one tested at .006 so I opted for the first.

(quoted from post at 17:49:59 11/08/21)

(quoted from post at 14:21:11 11/08/21) Swap the coils and resistor between them My vote is a bad coil. Jim

Click to expand...

I have another coil in the garage I can try. The one on it has .003 resistance and the other one tested at .006 so I opted for the first.

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ou must have one h3ii of a good Ohmmeter OR, you don't know how to read it. 3 milliOhms? Really?

Check the coil resistance again.

Set the ohm meter on the lowest range, probably about 200.

Check across the primary terminals with the coil out of circuit. A 12v coil should have about 3 ohms resistance. If it's lower, down around 1 to 1.5 it's a 6v coil or it's internally shorted.

You if your meter has an amp setting that is in range, connect it in series to the switch side of the coil and ground the points side. It should have about 3 to 4 amps draw. Work quickly, the coil will overheat if left connected for more than a few seconds!

If the amp draw is high, the coil is shorted or the wrong coil, either will cause the coil to overheat and can take out the Pertronix unit.

I have heard that solid wire wires are hard on a Pertronix unit, but I've also heard that only applies to use with a high output coil, which you don't have or need. I would not be concerned or blame the wires unless Pertronix says to change them for warranty purposes. Then I would go with spiral core wires, not carbon.

Call Pertronix. They have good customer service.

I put a new set in an A JD. It never started, just smoked the Pertronix. Was wired right, had the right polarity so don't know what happened. They replaced it so hopefully the new
set works.

Have Pertronix systems in my 1951 8N, and three generators. All have worked flawlessly for a number of years. 8N has about 150 hours on the Pertronix. I changed ALL the wires to resistance type; I think it will help. As others have said, probably the coil. I use standard 12V coils on my 8N and one generator; no ballast on either. No need for a "high output" coil on these low RPM engines, I believe. 8N starts almost instantly at 35*F. zuhnc

(quoted from post at 17:49:59) The one on it has .003 resistance and the other one tested at .006 so I opted for the first.

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(quoted from post at 19:35:52 11/08/21) A 12v coil should have about 3 ohms resistance. If it's lower, down around 1 to 1.5 it's a 6v coil...

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As Steve says.

On front mount coils for the old N series, I usually see around 2.5 to 3.0 ohms on a 12 volt coil, and usually 1.0 or slightly less for a 6 volt coil.

(quoted from post at 20:31:58 11/08/21) Have Pertronix systems in my 1951 8N....... I use standard 12V coils on my 8N and one generator; no ballast on either

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A 1951 8N should be a side mount distributor with a round can coil. These do not use a ballast resistor.
All front mount coils on the N series require a ballast resistor, to provide proper amperage to these.

You may have a fuel restriction.

(quoted from post at 15:26:57 11/08/21)

(quoted from post at 17:49:59 11/08/21)

(quoted from post at 14:21:11 11/08/21) Swap the coils and resistor between them My vote is a bad coil. Jim

Click to expand...

I have another coil in the garage I can try. The one on it has .003 resistance and the other one tested at .006 so I opted for the first.

Click to expand...

ou must have one h3ii of a good Ohmmeter OR, you don't know how to read it. 3 milliOhms? Really?

Click to expand...

well the multimeter I have has a bunch of settings. I think I put it on the first one to get the .003 and .006 readings.

(quoted from post at 17:43:24 11/08/21)

(quoted from post at 17:49:59) The one on it has .003 resistance and the other one tested at .006 so I opted for the first.

Click to expand...

(quoted from post at 19:35:52 11/08/21) A 12v coil should have about 3 ohms resistance. If it's lower, down around 1 to 1.5 it's a 6v coil...

Click to expand...

As Steve says.

On front mount coils for the old N series, I usually see around 2.5 to 3.0 ohms on a 12 volt coil, and usually 1.0 or slightly less for a 6 volt coil.

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I don't get it............on my multimeter at 20k setting I get over 8 ohms on one coil and 12 point something ohms on the other. How can that be? I measuring from the top post to the distributor cap side of the bottom of the coil. Right? The 8 ohm coil is the one that was on the tractor and runs 5 or 7 minutes before shutting off. Like I said before I'm a derelict when it comes to electrical.

(quoted from post at 12:04:42 11/13/21)I measuring from the top post to the distributor cap side of the bottom of the coil

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Sounds like you may be measuring secondary resistance. I think that will be in the range of 5,000 -- 7000-ohms.

I don't get it............on my multimeter at 20k setting I get over 8 ohms on one coil and 12 point something ohms on the other. How can that be?

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You are trying to measure primary resistance, which should be about a 1/2 an ohm to maybe 3.0 ohms, on a scale that is for between 0 ohms and 20,000 ohms. To get an accurate reading use a much lower scale, like 200 ohm scale or 1k ohms scale. When using an ohms scale that ends in k, as in 20k, multiply your reading by 1,000.


Here is a pic measuring primary resistance on a front mount coil. I believe this pic belongs to Bruce (VA), seen mostly on the Ford 9N, 2N & 8N Board, If so, Thanks Bruce!


This post was edited by jimtrs on 11/13/2021 at 09:48 am.