Why did my coil shock me?

[badge49]

Yesterday I decided to make a spiffy little bracket to cover my coil pack, as the clips on the spark plug wires are breaking off. The idea was to make a cover bracket that would better secure the plugs to the coil and prevent misfires by loose plugs. Take a look at my picture to see what it looks like:

Here's my problem: After bolting the new cover bracket on, I started the engine and it ran poorly. I turned off the engine and unbolted the two closest corners of the new bracket to releive the pressure holding the plugs down. I started the truck and it ran normally. With the engine idling, I reached my hand between the plugs and the new bracket (angled-up, still grounded)...and Ka-Pow! I got one hellova shock up my arm!

My theory is that with the engine running, there was enough power at the coil/plug seats to arc to the grounded metal plate. With the bracket pressing down on all six plugs, they misfired. When I reached in-between the bracket and coil, my hand acted as a short circuit.

My question is: How was the shock able to penetrate through the insullation of the plug wire? I've touched the plug connections before, with the engine running, and not been shocked. I'm going to play with this more and add a few layers of rubber under the bracket. Note to self: Don't reach in there again with the engine running...my arm still feels a little sore!:navajo:

 

[Black92LX]

your theory would be my guess.
As for why could be your insulation in the wires is getting old. Or for some reason there was enough of a gap between the coil and the plug wire to allow the current to escape.

 

[Texan01]

Sounds like you've got bad plug wires. but it's been known to happen to have arc-through at the plug boots. But 9 times out of 10 it's just plain bad plug wires.

 

[trailhead]

My Plug Wires On My Old Ranger Were Arcing Against One Another, A Trick To Try Is To Take A Spray Bottle, Fill It With Water. Then After Dark Or In A Dark Place With The Engine Running Spray A Mist Of Water Over The Engine Plugs/wires And You'll See Small Sparks Where Your Plug Wires And Insulation Is Thin, My Wires Were Arcing The Block And Coil Pack Also. It's Gotta Be Dark Out Tho.

 

[badge49]

Good idea, I might do some testing to see if the wires are bad. I hate to get rid of them though, the ones on there are 10.2mm and I can't find the Ebay company I got them from.

Anyone know what kind of voltage/amperage I took to my arm? It woke me up bigtime!

 

[Dan Whitaker]

In the neighborhood of 30,000-40,000 volts. I don't know how many amps.

 

[ThePhoenix]

those are some big wires...do you need them that big? just wondering

 

[badge49]

those are some big wires...do you need them that big? just wondering

I don't need them that big, but bigger is better. I think I paid like $30, which is a lot less than smaller Accell or MSD wires. Besides....they look cool

Is there an easy way to test the coil itself? Could it be a culprit?

 

[Texan01]

the coil is going to put out around 40,000 volts at some milliamps, basically not enough to really do more than say "Ow!" and numb your arm for a few seconds.
It's not the voltage that will get you, its the amperage.

Easy way to test the coil is to take it to Autozone or a parts store that does ignition module testing, they can test it, or you can use an ohm-meter and measure the coil pairs (there are 3 coils in it) and make sure they are relatively uniform.

You could have a crack in the epoxy top and when you torqued it down it opened it up a bit and allowed voltage to seep through. In all honesty you don't need much to keep them on, just about hand tight should do it.

 

[Turdle]

The coils are grounded to that bracket they sit on.
so
you have a bad wire-
or
a voltage leak at the coilpack. Are you sure you didn't crack the coil when you tightened it all down?

 

[badge49]

I'll pull the coil and take it to get tested. I'll clean it up too and see if there are any cracks. It concerned me that there was an arc even with no pressure applied to the plugs. I've got a couple OEM sets, so either way, I'll get the problem fixed.

 

[badge49]

Problem Fixed

I took the coil in to AZ. They tested the resistance and it tested good. I cleaned the coil and didn't find any problems. Then I closely examined each spark plug wire and found the culprit. #3 had a nice hairline crack in it that went to the core.

Thanks for the help guys, I'm going to throw the OEM wires back on and that will take care of any more arcing!:navajo:

 

[badge49]

Not to beat a dead horse or anything, but I thought I'd share an interesting article that I just found. This guy got an arc across 20mm! No wonder I got shocked when I touched the thing.

http://www.mr2.com/TEXT/DavidKucharczyk/ignition.html

 

[skoal_mint]

My Plug Wires On My Old Ranger Were Arcing Against One Another, A Trick To Try Is To Take A Spray Bottle, Fill It With Water. Then After Dark Or In A Dark Place With The Engine Running Spray A Mist Of Water Over The Engine Plugs/wires And You'll See Small Sparks Where Your Plug Wires And Insulation Is Thin, My Wires Were Arcing The Block And Coil Pack Also. It's Gotta Be Dark Out Tho.

Mix the water with salt, water alone is way harder for the spark to jump compared to salt water

 

[gijoecam]

Mix the water with salt, water alone is way harder for the spark to jump compared to salt water

True, but there are way more than enough free ions (from minerals) in plain ol' tap water to conduct the spark. Salt water will just cause other unrelated parts to rust. Don't try the test with deionized or distilled water though.... with no free ions in it, it's as good an insulator as rubber.

-Joe

 

[badge49]

My father recomended the salt water spray, but also suggested using an electrician's screwdriver to stick in there for an arcing point. However you test it, remember to not stick your hand in there!

I replaced the wires yeaterday, and did the plugs too since they were due for a change. No more arcing and no more missfires.:navajo:

On a side note: I'm surprised no one commented about my coil being mounted backwards and the stray noise suppressor attached to the alterered mounting bracket. I had to rotate the coil to fit the wrong-length 10.2mm wires I had, which required me to cut and alter the mounting bracket to move the boxy wire harness out. The noise suppressor was added to get rid of some engine interference I had with my HU. Just in case anyone was wondering