Spark Plug Wire Arcing at Spark Plug Wire Boot and Ignition Coil Connection

Continuing the discussion from Misfire… New wires arcing?:

I have a 2003 Pontiac Bonneville SLE and my check engine lights come on for periods of time…Sometimes it blinks on and off when accelerating or going up a hill…Autozone pulled a P0300 CODE which means random number 3 cylinder misfire…What is funny about this situation sometimes the car run smooth and then sometimes it don’t with the sputtering and acceleration problems…Yesterday I was able to see clearly the spark plug wire arcing right at spark plug wire boot that connects to the number 3 part of the ignition coil…Can this be a bad number 3 spark plug, #3 spark plug wire, #3 Ignition Coil Assembly and Ignition Condrol Module??? Or all parts above??? I am not that mechanically incline but if it is just a bad Ignition Coil that need to be replaced I can do that myself…What can this means spark plug wire arcing at the ignition coil and the #3 spark plug wire boot connection??? Please advise…

The root cause is usually a misfiring spark plug.

Over time a spark that is jumping can damage the plug wire or coil boot as the case may be.

With the spark plug out I would advise running a compression check on that cylinder. Low compression can cause a plug to misfire which in turn, yada, yada, yada.

Hope that helps.

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Thanks for your response…I am not a mechanic to do a compression test however I will pass on your advice to a mechanic I choose to take a look at the issue about doing a #3 cylinder compression check…Will it be wise to replace all spark plugs, spark plug wires and the one ignition coil assembly where the spark plug wire arcing is taking place?

Yes, if one set of wires is starting to arc, odds are the others aren’t long behind it

Yes,change them…thats an easy doityourself project. All you need to do is identify where all the wires go.

Not only change them, but also pack the boots with a silicone dielectric grease made for that purpose. It will help prevent future arcs, preserve the boots and sometimes will prevent arcing if the coil tower is cracked, which often happens when arcing has occurred for a while.

Thanks I will do just that…Replace them all at the same time. And pack the boots with the dielectric grease.

I would do the wires one at a time too, just to make sure you don’t cross up the connections


You are going to do plugs too aren’t you?

A little coil theory here if you don’t mind.

A connection is made to apply 12vdc to a coil. Current starts to flow but it is opposed by the induction of the coil. The voltage slowly overcomes the induction and more current flows. Current flow increases with time. At higher RPMs, it may only have 1/5000th of a second (200 microseconds) to build up, but in electrical time, thats a lot.

The current only flows through the primary of the coil which has fewer windings so it has less inductance so current flow builds quicker. As current builds up in the coil, magnetic lines of force build up around the coil. It is the build up of these that causes the inductance.

Now when the engine needs a spark, the connection that started the current flow is opened. When this happens, the magnetic field begins to collapse. The collapsing field cuts across the windings of the coil and when a magnetic field moves around a conductor, current is induced to flow. When the field collapses, it not only cuts across the primary windings, it also cuts across the secondary windings inducing current in those as well.

There are about 100 times as many secondary windings as there are primary windings. That alone would cause the voltage induced to be 100 times greater than the applied voltage, but there is more. There is also a time factor involved in that the field collapses many times faster (1.2 - 4 microseconds) than it builds up because of the extra resistance caused by the spark plug. So not only does the voltage go from 12vdc to 1200 v pulse, it an rise as high as 40,000 volts.

The voltage is determined by Ohms Law. I wont go into that but basically, the higher the resistance in the secondary circuit (coil + wire + plug), the higher the voltage. If the plug doesn’t fire, usually around 26,000 volts, then the voltage will go higher until it can find a path. It can jump from a weak part in the insulation of the wires or boots or it can arc internally in the coil, damaging it.

This is why it is important to change the plugs as well, and to always change them according to the maintenance schedule.

I would only add that only the correct plugs should be used. That info may be on an underhood sticker or in owners manual.

Here’s something that nobody else mentioned . . . as far as I know

Carefully check the coil tower(s) . . . they do sometimes wear out, which results in a poor fit, and often a misfire

Make sure the wires are in good shape . . . boots and insulation. I wouldn’t be surprised if the insulation is breaking down and arcing to ground, if they’re still the original parts

Considering the car’s 15 years old, it’s probably due for plugs by mileage, anyways.

Unless the spark plug gap has become really wide, my guess is the same as db’s above, there’s a bad connection between the coil and the top of the spark plug. Or the coil itself is shot.

Thanks everybody for your responses much appreciated…

In the future, take heed of that blinking CEL. You are supposed to stop the car as soon as possible to prevent serious damage to the catalytic converter.

Are you sure it wasn’t P0303? P0300 is the code for multiple random misfire.

I have missplaced the paperwork that Autozone printed out for me but it may have been the code you specified because I do remember clearly that the random misfiring was only happening with the number 3 cylinder only…I will make a definite note of when I see a blinking ÇEL to stop the car as soon as I can…Thanks

I had the same problem on my dodge caravan. I found I had a small crack I my coil pack! I taped UT up with electric tape! Running good! Engine check light off!!!

That’ll work until it rains…


Now I know you’ve probably taken care of the issue but. Seriously take heed to the blinking CEL light. I was driving down the free way just trying to make it to where I needed to be and the CEL started blinking… Paying no mind to it and just trying to get to my destination I was rolling a long… all of the sudden out of my read view mirror I see what looks to be a giant lit coal striking the pavment. Looking at the cigarette in my hand I thought “No way that was from me flicking my ash out the window” I quickly remembered reading about the blinking CEL and it meaning excessive unburned fuel could be going into your exhaust. quite possibly melting it… “Only in movies” I thought. fearing the worst I pull over and look under my car to see my exhaust glowing read and of course a section had melting off… I just laughed