Arcing on ignition coil

[Jean-Sebastien Stoezel]

Hi:

Last season I kept noticing an electric "pop" when I would shutdown the ignition on my car (this could only be heard when the engine would be off). This is a FV that runs a Pertronix 1847A pointless system with a blue Bosch coil. This system has been working fine with the engine.
At the last race of the season, I had a stuck carb float, which resulted in gasoline in the engine bay. A fire ignited when I shutdown the ignition.

Looking closer at this pop, I can now see that it is the result of arcing between the output terminal of the coil (secondary) and the primary terminals (both the 12V and the one input that comes from the Pertronix system). The arcing happens whether the plugs are connected or not.

Video demonstration here, the arcing occurs between the output and the left terminals: http://www.youtube.com/watch?v=Ph2jlRJ_nYQ

The bit of gray on the coil, which is RTV, which I used to secure the electric connections.

What's the cause of this? Faulty Pertronix? Faulty coil? How to fix it?

Jean

[GeoffRain]

Is there a hole or crack in the black plastic near the base of the secondary terminal?

[Jean-Sebastien Stoezel]

I will have to go have a closer look. It has been arcing towards both terminals I should add.

Is there a hole or crack in the black plastic near the base of the secondary terminal?

[BLS]

Jean,

You have some conductive path between the coil HT lead (the center terminal) and the ground side (the connection to the distributor) terminal. The arcing indicates a bad place in the coil in my opinion. Change coils...

Regards,
Barry

[Jean-Sebastien Stoezel]

I checked with another coil and I still get the same arcing... I also tried another Pertronix model, same thing.

The only time there is no arcing is when the Pertronix is not mounted in the distributor. That is when the chassis of the Pertronix is not grounded.

Jean

[Pop Chevy]

Did you try a different wire(coil or plug) or wires ? If that high tension spark has no place to go, it will find a place. Electricity follows the path of least resistance.

[FVRacer21]

Jean,

Not familiar with this ignition system, but some general suggestions.

1. Once you get arcing you leave a carbon track which does not get better. Dirt, oil, grease even sweat can provide the initial start. I would try to find a non black top coil, make sure the wire seal is good and maybe use some silicone grease used for current high voltage systems.

2. Is this the right coil for the application? There are resistor and non-resistor coils - using the wrong one might cause a higher spike than normal.

3. I can't believe the silicone sealer you are using is causing a problem, but clean it off good with an electrical cleaner - clean and dry is the best condition.

4. (Edit - What he said above.) When you shut off the ignition it is just like the points opening in a regular distributor - normally with the engine running any stray spark should follow a path of least resistance to a spark plug. By just turning it on and off with the engine not running - you are creating a situation that does not normally occur. But it could and did - hence your fire - still thinking you have created a path of less resistance for the spark - look at the cap, wires, etc. for something that would have encouraged it.

5. Maybe something is defective with the unit. When you kill power to it, maybe it supposed to bleed down slowly so you don't get the coil to collapse - any electrical engineers out there? Have you called Pertronix?

That's all I have right now - keep us posted.

ChrisZ

[BLS]

Did you try a different wire(coil or plug) or wires ?

Given that another coil does the same thing, this is probably my next guess as well.

OTOH, with the pertronix not installed, there is no firing induced. We tend to think of the coil as a transformer but it also operates as an inductor. The pertronix (or points) ground the coil causing current flow to take place, when the circuit is opened the field collapses causing the high voltage "spark". You can simulate by placing a wire from the coil to ground and lifting it (open circuit) then grounding again, the same thing points or pertronix are doing. The collapsed field voltage has to go somewhere and it will be the path of least resistance. I'm going to guess Pop Chevy is correct.

Also, could be a bad distributor cap or rotor that does not allow current to flow with less resistance than that between the coil terminals. I would connect a spark plug directly to a good lead from the coil HT post and test with a wire connected between the coil ground side and ground. If the plug fires when the ground wire is lifted then the problem must be in the cap or rotor. I think...

[Daryl DeArman]

The Bosch Blue coils you are using (the one in the video and the one you replaced it with)...are they the same P/N? It is my understanding that there are several different model Bosch Blue coils---some 1.5ohm, some 3.0ohm, some oil filled, some not.

For racing and the pertronix I believe the preference is a 1.5ohm. If you use an oil-cooled model they are happier when mounted vertically (terminals at top).

Further, having the ignition switch on for extended periods without the engine running can damage components....perhaps that is what has happened. Crank engine to build oil pressure then hit ignition switch. Don't turn on switch and then crank.

[BLS]

Jean,

I need to learn to read... Missed the fact that this happens when you shut off the ignition. I thought it was arcing while you cranked the engine. The ignition "fires" when the flow of current to the coil is interrupted. In the case of points, it happens when the points open, breaking the coil circuit. The electric field collapses and you get the pulse of energy that creates the spark. In the case of the petronix it works the same way. Turning the ignition on and then off is the same exact thing, the coil is energized and turning the switch off causes the field to collapse. As I mentioned earlier, you could turn the ignition on and use a wire connected to the coil negative side to ground. With the wire on ground the coil will energize and lifting the wire from ground will cause it to fire. In the case of points, if the points were open when the ignition was turned on and then off nothing would happen as no current could flow through the coil to create the electromagnetic field. If the points are closed when the ignition is turned off and on then you should get a "spark", but since there is no alignment between the rotor and dist cap, the energy has to go somewhere else, but I've never thought about where it goes. Path of least resistance clearly, but what is that? In your case it appears we know what it is. I suppose the pertronix might be slightly different in that respect since it is an electronic device and I do not know its internal circuit.

Maybe what you see is normal since the energy must go somewhere. I'll have to think about it some more or maybe somebody smarter will chime in.

[Jean-Sebastien Stoezel]

Thanks for the replies. I got the part numbers for the coils and looked them up on this link: http://www.ratwell.com/technical/BlueCoil.html

Both of the coils I have are 221 119 027, which are 3.4 ohms primary (these seem to be listed as the good ones on this website). This seems to show it has the resistance balance inside.

Both arc, one I should say seems to arc a bit less. It has an orange/brownish (from the website above it seems like an original German model) insulating top while the other one has a black insulating top (looks like what's referred to as model from Brazil).

The German model does not have residues of RTV.

I should say that the arcing occurs both when it's connected to the distributor cap and plugs (I guess it also depends of the position of the distributor shaft).

Barry, I see what you mean, I think. The posts seem much farther apart than the distributor rotor would be from any of the 4 posts inside the distributor cap. One would think that the path of least resistance would be towards one of the posts in the distributor cap. Unless a plug wire is damaged, or a plug is removed.

Again the engine worked like this all year last year.

I will have to do the experiment again when I'm at home tonight. Maybe the pop that I hear effectively happens inside the distributor cap when everything is wire, and not on the posts...

[racerdad2]

Are you shutting the ignition off first, then the master ? If the ignition circuit is separate from the master, it would seem the coil would dissipate at engine shut down, then killing master would have no effect ? Just thinking out loud....

[Dick R.]

Are you shutting the ignition off first, then the master ? If the ignition circuit is separate from the master, it would seem the coil would dissipate at engine shut down, then killing master would have no effect ? Just thinking out loud....

Also, aren't Pertronix's points eliminators likely to fail if left on without the engine running? Even with points isn't normal practice to first shut of the ignition switch and then the master switch?

Dick
85 VD with points and a Bosch blue coil.