I don’t know why I’m even wondering about this since I installed the pertronix kit years ago and the car has run fine ever since, but it occurred to me tonight that although I’ve got 12 volts running to the unit inside the distributor, my stock type coil is still fed only 6.5-8 volts from the resistor wire. Since i no longer have points to fry, should I bypass the resistor portion so my coil gets fed a full 12v all the time? Like I said, the car runs great as is, but maybe I’m missing out on better performance from some extra juice to the coil.
The coil is probably designed around the lower voltage and will overheat if you run the full 12 volts to it. You can buy a coil that it designed to run without the ballast resistance that will have higher output but there is another factor. The power is switched at the key. That switch is rated for the amount of current that the stock coil pulls. When you eliminate the series resistance, the total resistance drops which means that the amount of current being switched goes up. For example if the alternator is putting out a solid 13.6 volts, and you have a .6 ohm coil you will be pulling 22.66 amps through the switch. You will feel the key actually getting hot to the touch and the switch wont last very long. The stock coil plus the resistor wire add up to probably no less than 3 ohms. In that case the switch is only handling 4.533 amps. The best work around is to use a relay to switch the coil power and then you can easily run a hotter coil with a full 12+ volts. The pedapter from Rocketman is a good way to get this accomplished.
Hey all,
So I installed an Ignitor I (original) and a 1.5 ohm Flamethrower coil on my 69 XR7. Factory tach of course, with pink wire, etc…It’s better than the old points, but I am still experiencing obvious misfires at idle and sputtering throughout what I would call “the power band” when driving. I temporarily connected the Ignitor module (red wire) straight to battery to see if it ran any better…it did not. As such, I returned the module red wire to the “I” post on the starter relay (where I initially had it) and it is receiving a steady 11.4 volts or so. Positive on the coil is connected to the old resistor wire.
Today, in a fit of desperation to try and solve the misfire mystery I ran a jumper wire from full battery to the positive coil connection to see if it made any difference…this time, it did. Flawless idling at last. Now there were of course side effects to this that I did not expect.
This configuration obviously completely bypasses the tachometer AND ignition switch as, while running, there was no reading on the tach and of course when I tried to key off the engine, it just kept running. This, in addition to the fact that I know these coils are not designed to take a full constant 12v, does not lend itself to a final remedy. It does however (at least in my novice opinion) finally identify what the problem is…I have a low voltage condition at the coil.
So my thoughts are that I either have a bad ignition switch or a bad tach. Neither of these situations are very palatable, but I wanted to get some other more learned opinions on the matter and my next steps…possibly leading to a permanent remedy.
Thanks…
I’d replace the 1.5 ohm flamethrower coil and go back to the Ford yellow-top coil to see if that makes a difference.
Never had a yellow top…car came with a Napa 1.5. Already swapped it out. Didn’t work…put the flamethrower back.
When you are cranking the car the ignition switch bypasses the resistance wire and supplies full battery voltage to the coil. So the coil gives a good hot spark when cranking. Voltage measured at the coil on a cold day will be slightly less than 12 volts when cranking due to the starter load.
When the engine is running the alternator raises system voltage to 13.8 - 14.2 volts. Voltage measured at the coil with the engine running should be about 11.5 - 12 volts. This assumes good connections and a charging system that is working properly.
Whatever your car’s problem might be, it is not being caused by the resistance wire circuit. You likely have the timing set improperly, or a vacuum leak, bad PCV valve or some other simple tuning problem.
[quote=“Royce”] Voltage measured at the coil with the engine running should be about 11.5 - 12 volts. This assumes good connections and a charging system that is working properly.
[/quote]
If you re using a 3 ohm coil (note: pertronix sells both 1.5 and 3 ohm coils), then Royce’s advise above is correct, however if you are using a 1.5 ohm coil (ie a stock coil), then the voltage measured at the coil will be in the 8 to 10 volt range. Running a 1.5 ohm coil with 12 volts will overheat the coil and in worst case scenario, the coil will explode! The resistance wire from the ignition switch to the bulkhead connector, drops the voltage from 12 volts down to the 8 - 10 volts at the coil.
Coach Jack
I ran a jumper wire from full battery to the positive coil connection to see if it made any difference…this time, it did. Flawless idling at last.
This tells us that an increase in voltage at the spark plugs is improving things. (the coil multiplies the input voltage so a higher input voltage equals a higher output voltage) Voltage pressure is what makes the spark jump the gap. Be sure to confirm that the gap is set properly at .034.
Thanks…initial timing is currently at 10 degrees BTC and I have a full 18 Hg of vacuum at the intake. Plugs, wires, cap, rotor, battery, Pertronix module and coil are all new. Will check on the PCV, but I can’t think of anything else. Oh, and the carb was rebuilt two months ago.
Thanks,
Coach…when you say 8 to 10 volts at the coil, do you mean measuring from + coil terminal to battery/chassis ground or do you mean across the coil terminals?
Thanks…car has brand new NGK plugs with factory se .034" gap.
Thanks…car has brand new NGK WR5 plugs with factory set .034" gap.
Sorry for the last double post…
[quote=“anthem75”]
Coach…when you say 8 to 10 volts at the coil, do you mean measuring from + coil terminal to battery/chassis ground or do you mean across the coil terminals?[/quote]
Anthem,
Measure the voltage from the + coil terminal to ground.
Coach Jack
Ok…I have 11.4 - 11.5 volts in that configuration. But as soon as the engine reaches operating temperature, the misfires (mostly while in gear) begin. I waited until the engine was hot the other day, then swapped the Flamethrower coil out for my old Napa unit (which was cool; and same resistance) and it ran much better…for a few moments. Once it heated up, the misfires began again.
It should be noted that in this setup, the idle improves dramatically when I INCREASE the voltage to the coil by jumping over to full battery temporarily.
Anthem,
Measure the primary resistance of your coils using an ohmeter across the + and - terminals of the coil. If you read 1.3 to 1.5 ohms, you risk blowing the coil by running full voltage to the coil. If you are reading 3 ohms across the coil, then you are safe running 12 volts to the coil. Do you know if your car has the resistance wire from the ignition switch to the bulkhead or was it replaced with a regular wire? you can verify this my measuring the ohms from the coil side of the ignition switch to the + side of the coil, roughly 1.5 ohms would indicate you have the resistance wire in place.
Coach Jack
Coach…primary resistance is almost exactly 1.5 ohms. Secondary resistance is approximately 9k ohms. I cannot confirm the existance of the resistor wire. Please forgive my ignorance, but can you clarify further what you mean by “measuring ohms from the coil side of the ignition switch, to the + side of the coil…” ?
1.5 ohm primary and 9K secondary resistance values are good, but a 1.5 ohm primary needs a resistance wire.
The ignition switch has a C or Coil connector as one of the wires in the ignition plug. Disconnect the plug and place one of the ohmeter leads on this wire and the other lead on the + coil.
Coach Jack
Thank you sir…