Killing Ignition Coils.

[Smedley]

Original issue - 70 Bronco, 302, centech harness, one wire alt, ready 2 run distributor, new battery, and a 4bbl. Truck has been running great for a year or more, nothing has changed. The fluid in the radiator was looking a little brown, so I decided to flush the engine. That went well and the truck fired right up after. Everything in the engine bay got wet in the process. While driving it around later that day, it would suddenly die. Probably 3 or 4 times. It started back up each time, although some of the starts took a little more time. It did the same the next day. Then it died and would not start back up. Cranking fine, getting fuel. No spark.

Continuation from previous issue. Figured out that I had an issue with the coil. I think I burned up the first one because I left the key in the ON position for a while listening to music while working on the Bronco. Swapped the coil and got it fired up. Now I am smoking coils. With a new coil, at battery I have 13+ v. At coil I have ~13 v. After I start and run for a bit, I shut it off. Now it won't start. Then I have 13v at battery and 11 or less at coil. Happened 2 times. Thoughts?

 

[DirtDonk]

Should not hurt anything in the accessory position. If it does, you have it wired incorrectly.
The ignition circuit is one of only two that get power in the ON position only. Never an ACC.
So check your Wiring first of all.

However, as long as it’s the correct coil, there’s nothing unusual about the voltage you’re getting. As far as hurting the coil that is.
The change in voltage is concerning, however. If it reads 13 V at the battery at 13 V at the coil, it should do so all the time. Not sure why you’re getting 11 afterwards, but I would check all spices and connections for a moisture and corrosion.
Are you reading this with the coil disconnected, or connected?

And in the meantime, have you checked coil power in the ACC position? If you’re getting power in ACC, you should change the wiring around.

 

[Smedley]

Thanks Paul. I was not having any issues before flushing the coolant system. So, it's new. I could not figure out why this would cause the issue. I assumed the coil died because I left it in the accessory position, based on info I received from others. I cannot confirm it. I'll check coil power both in ACC and during start later today.

 

[Oldtimer]

Does Centech harness have a ballast resistor?
Could it be shorted out?
Does the coil for a "ready 2 run distributor" expect 12v or a lower voltage supplied by ballast resistor?

 

[Smedley]

Not running a ballast resistor.

 

[76Broncofromhell]

Should not hurt anything in the accessory position. If it does, you have it wired incorrectly.
The ignition circuit is one of only two that get power in the ON position only. Never an ACC.
So check your Wiring first of all.

This.

The coil is not meant to be powered when the engine isn't running.

 

[Smedley]

I misspoke in my original post, I did not leave the key in the ACC position, I left it in the ON position. I'm sure this changes the above responses.

 

[DirtDonk]

Yep. So at least that part is nothing to worry about.
Now we just have to figure out why you’re killing coils.

What are the part numbers and brands of these coils? All the same?
Maybe you’ve got a couple that aren’t meant to run on the full 12 V. Stock types used lower voltage, which is why Centech includes a ballast resistor in their harness. But if it’s not installed, the coils must be capable of running 12 V.
If I’m not mistaken, usually that takes a 3-ohm resistance or more rating.
But don’t hold me to that, since I never bothered to really memorize all the ohm ratings and capabilities of coils.

Not sure what changing the coolant would have triggered either. Likely nothing on its own, other than messing around under the hood might’ve jostled some wires.
The lower voltage that you read that one time could be from messed up wires, loose connection, or all that water finding its way into the Harness and connection somewhere.

 

[Smedley]

I found a blown fuse on my headlight upgrade, it was an inline fuse and completely melted. I replaced that. Lights work fine. I have tried a couple of new coils. 12.5 volts at battery, 12.5 volts at coil in the ON position, 11ish on crank at the coil. However, I am not getting a spark from the coil wire. I pulled it from distributor, rested it on exhaust manifold and there is no spark.
The new coils I have tried are the same that were on it. It has run like this with no problem for the last couple of years.

 

[gnpenning]

The connections for low voltage wires on the coil are marked with a - and + sign. Which one is going to the distributor?

 

[Smedley]

Neg

 

[Smedley]

Well after chasing parts for a bit, I replaced the ready to run distributor. Fired right up. Fingers crossed.