Arcing around base of spark plugs.

[Dieselman966]

I can see some arcing around the base of at least 5 spark plugs on my galaxie.  And one has an arc that is visible about every 3 seconds which seems odd.  What causes the arcing around the base of the spark plugs? I've never noticed it before.

[cjshaker]

No, that's not normal. What ignition and plugs are you using? Are you sure it's not coming from the wires? I've seen that plenty of times, always indicating that the wires insulation is breaking down. I'm wondering if you used a large amount of anti-seize on the plugs when you installed them? That could inhibit the grounding of the plug and cause it to arc outside of the threads. I'm not a fan of using anti-seize on plugs for that reason. I understand using a small amount in aluminum heads, but I think it should be used very sparingly. I also wonder if the sparkplug threads in the head were dirty or rusty (if using iron heads), which could also inhibit the grounding.

[Dieselman966]

I'm not sure what plugs or wires are in it. Same stuff that came with the car.  What does everyone run on these motors? And I'm guessing this could be the cause of why it seems to be miss firing.  Motor seems to run rough.

[machoneman]

You should do an Ohm test on a few wires. It could be as noted poor grounding but an Ohm test will tell if it's the wires.

I'd also inspect/clean/replace the engine-to-firewall ground strap as often folks take them off or fail to reconnect it after say painting the compartment. 

[preaction]

You could have flashover which can happen if the insulating boots of your plug wire is to short and doesn't cover the insulator of the spark plug and then there is  corona, in many cases corona is mistaken as spark plug flashover however corona is the glowing that appears above the plug shell around the base of the insulator. This condition is caused by the electrical stress in the air adjacent to the insulator-corona is in no way detrimental to spark plug operation and will cause a brown or grey deposit on the insulator top just above the shell.

[Dieselman966]

You should do an Ohm test on a few wires. It could be as noted poor grounding but an Ohm test will tell if it's the wires.

I'd also inspect/clean/replace the engine-to-firewall ground strap as often folks take them off or fail to reconnect it after say painting the compartment.

What kid of ohm's am I looking for on a wire? Is there a range?

[Dieselman966]

You could have flashover which can happen if the insulating boots of your plug wire is to short and doesn't cover the insulator of the spark plug and then there is  corona, in many cases corona is mistaken as spark plug flashover however corona is the glowing that appears above the plug shell around the base of the insulator. This condition is caused by the electrical stress in the air adjacent to the insulator-corona is in no way detrimental to spark plug operation and will cause a brown or grey deposit on the insulator top just above the shell.

I have to spark plugs that are clear arcs.   The others are like a ring of electricity around the base of the spark plug.

[GerryP]

It seems you are experiencing a corona on the plug.  It is not really abnormal or indicate a problem.  This sometimes occurs when environmental conditions are just right.  Normally a cooler, damp night and some dirt or oil on the plug or in contact with the plug.  You can pull a plug and inspect the insulation.  A corona leaves what looks like a tea stain on the porcelain at the crimp of the metal shell.  It's not affecting the performance of the engine.

[GerryP]

You could have flashover which can happen if the insulating boots of your plug wire is to short and doesn't cover the insulator of the spark plug and then there is  corona, in many cases corona is mistaken as spark plug flashover however corona is the glowing that appears above the plug shell around the base of the insulator. This condition is caused by the electrical stress in the air adjacent to the insulator-corona is in no way detrimental to spark plug operation and will cause a brown or grey deposit on the insulator top just above the shell.

Oops!  Didn't see you already covered it.

[Dieselman966]

It seems you are experiencing a corona on the plug.  It is not really abnormal or indicate a problem.  This sometimes occurs when environmental conditions are just right.  Normally a cooler, damp night and some dirt or oil on the plug or in contact with the plug.  You can pull a plug and inspect the insulation.  A corona leaves what looks like a tea stain on the porcelain at the crimp of the metal shell.  It's not affecting the performance of the engine.

I learned something new today. I have never seen this before but I do remember seeing the line the the spark plugs befpre.

[machoneman]

You should do an Ohm test on a few wires. It could be as noted poor grounding but an Ohm test will tell if it's the wires.

I'd also inspect/clean/replace the engine-to-firewall ground strap as often folks take them off or fail to reconnect it after say painting the compartment.

What kid of ohm's am I looking for on a wire? Is there a range?

https://www.championautoparts.com/Technical/Tech-Tips/Defective-Spark-Plug-Wires.html

[cjshaker]

You said you had 2 that were clear arcs, which is definitely an issue, whether it's plug grounding, wire insulation or plug gap. That would most definitely cause a rough running issue as well. It can also happen at the cap. A corona, or glowing around the plug, not so much, but arcing is definitely showing that you have an issue.

[fastback 427]

On my msd 7 with the hvc coil, i have seen the arcing around the base of the plug wire boot, at night. No misfire though. If memory servs i think that coil has almost 2 amps, might be the reason.

[Joe-JDC]

MSD 7 gold boxes have a tendency to melt the center electrode, and cause a misfire, especially on smaller diameter plugs.   Joe-JDC