Coil

[PNYGTA]

OK here goes.

My understanding as far as the electrics of my 66GT are limited so please be gentle.

What is happening is that while driving, the engine is constantly surging/hunting, even when initially taking off and when changing up to 2nd the engine is not as smooth as it has been.

My mechanic has diagnosed this as an electrical issue, specifically the coil is not receiving the voltage that it should be getting, he has told me that the coil is a 12 volt coil and the alternator is not providing enough voltage. The suggested repair is to install a relay which will provide 12 volts directly from the battery when needed.

Does this sound feasible.

Cheers

PNYGTA

 

[B67FSTB]

IIRC then an original ignition system is operating at a voltage of 9volt.
Thats why you find a resistor wire on the electrical wiring diagram from the ignition key to the plus pole of the coil.
Only when cranking the engine , this resistor wire will be shortcut by the starter relais.
Because during cranking the engine , The voltage on the battery terminals will drop by a few volts.So the coil gets enough voltage during cranking the engine.
Measure the voltage ( min at the chassis and plus at the coil ) during engine operation.It should be 9 volts.
You can replace the condensator at the disrtributer to be sure it isn't that little thing that causes so much trouble.
While you are there , change the ignition points.. :confu
B.

 

[apollard]

+1. When running, the original electrical system drops the voltage at the coil through the resistor wire to extend the life of the points. Only new cars with electronic ignition run full battery voltage at the coil (or older cars converted to electronic ignition). Note: some electronic points conversion modules (for example Pertronix Ingnitor I) still need the dropped voltage.

 

[AzPete]

In my experience, a coil that is getting low voltage would cause a miss (sudden stumble and recovery)....not surging. I would look more at vacuum leaks or fuel delivery issues if the car is really surging....as in a rather smooth change of idle speed as if the gas is pressed and released. As for the coil power, others covered it.

 

[B67FSTB]

In my experience, a coil that is getting low voltage would cause a miss (sudden stumble and recovery)....not surging. I would look more at vacuum leaks or fuel delivery issues if the car is really surging....as in a rather smooth change of idle speed as if the gas is pressed and released. As for the coil power, others covered it.

Like power valve failure on the carb , accelerator pump diaphragm or secundary diaphragm failure?

 

[AzPete]

Like power valve failure on the carb , accelerator pump diaphragm or secundary diaphragm failure?

Those plus depending on the carb brand, it can be in the transition circuit into the acceleration circuit.

 

[Midlife]

Severe timing advancement can also create surging during steady driving conditions.

 

[PNYGTA]

Thanks for the replies all.

Just a little extra info, which in my case can be dangerous, I am running an ignitor I instead of points and my understanding is that this would be why I have a 12 volt coil fitted, that is what I got with the car two years ago, I have also read that with this set up it is normal to bypass the pink resistor wire under dash, therefore providing 12 volts to the coil in run mode.

Electrician has installed a bypass and relay in the engine bay and was still unable to work out why the alternator was fluctuating output so much, he has recommended that I fit a more modern alternator than the original one I have now. I have agreed to this as I would rather a more reliable car that looks original rather than one that is original but unreliable.

Any further thoughts would be appreciated.

Cheers

PNYGTA

 

[B67FSTB]

You can switch the voltage regulator by an electronic one !!
Old voltage regulators have relais in them as electronic one have transistors in them.
I would do this first as this is cheaper ($15 I think). IMO.

I have still the original alternator but with an electronic voltage regulator , and it works fine.
You don't need a high amp alternator when your car stays stock even when you put Halogen headlights on it.

 

[apollard]

You need to determine if it is an Ignitor I or Ingitor II. If it is a I, then bypassing the ballast resistor (pink wire under dash) to the coil thereby increasing the voltage accross the coil will likely shorten it's life Wiring it this way causes it to pass more current through the coil than it was designed for).

See the second page, figure 3 for how it should be done on our cars.
http://www.pertronix.com/support/manuals/pdf/ignitor12vneg.pdf

I would agree that a modern alternator is an improvement, but as Bruno points out, a modern voltage regulator will solve the fluctuation problem. I also agree with the others that point you to a fuel or timing problem for the surge you are seeing. The voltage can not fluctuate enough to cause a surge if the battery is at all good on our cars (modern EFI is different, it needs very stable voltage, but even it has built in circuits to prevent alternator problems from causing issues).

 

[AzPete]

The voltage surge you are seeing MAY be caused by the fact that the engine is surging and the slower speed causes the alt. output to drop...........as these old units do at an idle or a low idle. Pull the alt and take it to a shop for independent testing.