electronic ignition

cheif · Oct 31, 2014

After reading glowing reports of the petronics ignition on this forum I decided that is just what my 74 3000 needs . The instructions that came with the set are kind of generac Especialy in regards to the coil. Do I have a resisted coil? When they speak of the resistance are they referring to the circuit resistance or just the coil? The instruction sheet refers to engines with four, six, and eight cyl but no mention of a three. I hope some of you will clear the fog from my old brain. Any hints on how to do this job will be much appreciated.
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Sean in PA · Nov 1, 2014

The 3 cylinder 4000 originally had a coil that required an external resistance in its 12 volt system. That external resistance was originally provided in the form of a resistance wire that looked like a very thick section in the wire that went from the key switch to the coil, it looked sort of like a fusible link if you've ever seen one of those.

Many were changed over the years when the resistance wire went bad or when a previous owner was rewiring and didn't know about the resistance wire. So you need to determine exactly what you've got, whether it still has the original resistance wire or whether it has been replaced by an external ballast resistor, or whether the coil has been replaced with one that does not require an external resistance.

Sorry I haven't installed a Pertronix myself, so I can't help with the 3 cylinder translation of the instructions, but from what others have said, if you call Pertronix for help they should be willing to explain it to you.

Texasmark1 · Nov 1, 2014

The idea is limiting current through the electronic switch in the unit as compared to the ignition points. If you don't limit it, it will over current the switch and power dissipation internally will kill it.

I'ts been a long time since I installed one so I don't remember the exacts.

The DC resistance in the series circuit can either be in the wire of the coil or in an external resistor. Ohm check of the coil will give you that answer. Auto parts carries them and I have bought them with taps so that you can make your own. As I recall there was a tap for 1.5 ohms and another for 2.5, or you could wire them in series for 4 ohms....thereabouts...don't remember the specific resistances.

I think the current max is 4 amps but your directions should tell you the minimum value of resistance. If you get too much R you will just limit the energy in the spark and the engine could misfire but you aren't going to hurt anything in the unit with too much.

So if your generator is running and you are getting 14.5v on your battery while running, it's 14.5/4 or a min of 3.6 ohms in my example and that could all be in the coil, part in the coil and part in a resistor or impractically, all in the resistor.

One thing I found with the ones I installed was that the ignition timing was not real critical. Dwell had a lot wider range. Matter of fact, to "time" them I would go cw and then ccw getting to the misfiring in both directions and set it in the center. Not very scientific.

On number of cylinders, that can be related to average power in the unit. For a given rpm, the fewer the cylinders the lower the average current for a given peak current (V/R) which would reduce the average dissipation in the electronic switching device and allow it to run cooler, last longer. Heat kills silicon.

HTH,
Mark

JMOR · Nov 1, 2014

(quoted from post at 09:51:32 11/01/14) The idea is limiting current through the electronic switch in the unit as compared to the ignition points. If you don't limit it, it will over current the switch and power dissipation internally will kill it.

I'ts been a long time since I installed one so I don't remember the exacts.

The DC resistance in the series circuit can either be in the wire of the coil or in an external resistor. Ohm check of the coil will give you that answer. Auto parts carries them and I have bought them with taps so that you can make your own. As I recall there was a tap for 1.5 ohms and another for 2.5, or you could wire them in series for 4 ohms....thereabouts...don't remember the specific resistances.

I think the current max is 4 amps but your directions should tell you the minimum value of resistance. If you get too much R you will just limit the energy in the spark and the engine could misfire but you aren't going to hurt anything in the unit with too much.

So if your generator is running and you are getting 14.5v on your battery while running, it's 14.5/4 or a min of 3.6 ohms in my example and that could all be in the coil, part in the coil and part in a resistor or impractically, all in the resistor.

One thing I found with the ones I installed was that the ignition timing was not real critical. Dwell had a lot wider range. Matter of fact, to "time" them I would go cw and then ccw getting to the misfiring in both directions and set it in the center. Not very scientific.

On number of cylinders, that can be related to average power in the unit. For a given rpm, the fewer the cylinders the lower the average current for a given peak current (V/R) which would reduce the average dissipation in the electronic switching device and allow it to run cooler, last longer. Heat kills silicon.

HTH,
Mark

retty good answers Mark. Pertronix apparently worries more about peak currents, as they recommend higher resistance for smaller number of cylinders. The fewer the number of cylinders, the longer the dwell and with coil current being a time function, the longer the dwell, the higher the current rises & if long enough, is finally limited only by resistance as coil saturation is reached. Hence, the recommendation for larger resistance for engines with fewer cylinders.

Ultradog MN · Nov 1, 2014

I installed a pertronix ei kit in a 3 cyl about 9
years ago.
I don't remember much about it now
But do remember it was pretty straightforward. The
red wire went to the power source and black wire
went to the coil.
At the time I did not know about the resistor wire
and it ran fine on the lowered voltage for several
years. Only when I put that engine in another
tractor did I add a second wire to feed full volts
to the module, and retained the resistor wire to the
coil.
Sean, the resistor wire does not go all the way back
to the switch.
There is a bullet plug connector by the solenoid and
the resistor wire plugs in there.

mooboy · Nov 1, 2014

Ultradog has it right. The resister wire begins at the bullet connector under the gas tank near the solenoid. If you use the stock coil you need to connect ahead of the resistor wire and run a separate wire to the Pertronix module so it gets the full 12 volts. Or get a coil with about 3 ohms primary resistance and bypass the resistance wire altogether. If you do that you can power the Pertronix module at the + terminal of the coil. That is what I did on the 3600 Ford that I have. BTW, best money I ever spent on that tractor. Runs much better and has consistent strong spark.

Texasmark1 · Nov 2, 2014

Hmmm. Guess it would help for me to see/understand their
circuitry and is their switch an SCR or a MosFET? I am keenly aware
of L di/dt and C dv/dt and all that and agree with what you said
about the effects of long dwell times, if allowed to persist with the
slower firing rate of fewer cylinders.

Mark

electronic ignition

cheif

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Sean in PA

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Texasmark1

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JMOR

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Ultradog MN

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mooboy

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Texasmark1

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