coil arcing madness

**feral4mr2** · 23-05-2009, 11:24 PM

i've been chasing a miss at idle on the vermin. tonight after i replaced the dist (oil leak), re-set static timing and set base timing i was playing around with it idleing. it still had the small miss at idle and slight hesitation when 1st open reving.
i proceded to pull a lead off a spark plug and noticed when i did this the + and - on the coil arced out on the coil center pole. it looked like there was even a small arc off the coil lead onto the eng fan..

it does this on every lead (1 through to 4) that is pulled off.
so i replaced the coil with another i have, same thing. i cannot see a arc when the engine is idleing, but thinking this could be the source of my miss/hesitation.

anyone come across this? could a dodgy igniter be to blame?

**StuC** · 24-05-2009, 09:18 AM

every time i've seen this feral it has been coils and/or leads. however, having said this they have been cars with 200+k on them and still running original items. with all of the heat an adub would generate under the bonnet it isnt outlandish to suggest that the leads and coil shielding is shot and need to be replaced. start there first and see how you go.
It is also easier to see the arcing at night as a handy tip

**feral4mr2** · 24-05-2009, 09:56 AM

is a new set of leads too. i might order a new coil and see how that goes, seems wierd to do it on 2 coils i have. plus i'll try the other igniter i have.
i'll turn the lights off in the shed next time, i was doing it last night and just used my body to block out the light.

thanks

**brett_celicacoupe** · 24-05-2009, 10:15 AM

if the current has nowhere to go then the voltage will continue to spike until it can find a path.

this is why its a bad idea to pull leads off because it begins to break down insulation within the coil or other places

**Moppitt** · 26-05-2009, 05:46 PM

Originally Posted by brett_celicacoupe

if the current has nowhere to go then the voltage will continue to spike until it can find a path.

this is why its a bad idea to pull leads off because it begins to break down insulation within the coil or other places

Miscellaneous fact: BMW coil-packs tend to fail if you do this once... It makes checking for a failed coil without breaking each one you check an interesting task.

Happily most coils arent as fragile as that.

Not sure what this could be but am interested.

Subscribed.

**Dazza** · 28-05-2009, 10:06 AM

The spark will be jumping to the positive and negative of the coil if it is the easiest path for the spark to follow. The spark must be having trouble getting through your leads or distributor. My first thought was it is a faulty coil lead. You could use a multimeter and check the resistance of the leads. Another problem i have seen is that the end of the rotor button gets burnt and is like a hard black insulator that will not let spark travel to the pins on the distributor cap. You can use some emery paper on the end of the rotor button until you rub it back to the brass so the spark can now travel across to the pins inside the distributor cap. Also check the pin in the centre of the cap to make sure it hasn't fallen out or isn't seized and jammed up high in the cap. It should be spring loaded so it will push down on the centre of the rotor button.
Your miss and hesitation down low in revs could be caused by a lean fuel mixture at idle. Make sure you have no vaccuum leaks. It could even be a leaking manifold gasket.

**feral4mr2** · 28-05-2009, 10:18 AM

the coil lead is new, though i will check out the distributor and it's components.

i will be pulling the inlet manifold off soon, the gaskets i did make myself a while back so it is possible there could be a small vacum leak.

cheers.

**GT1978** · 28-05-2009, 12:18 PM

Also might want to check the condition of the earth to your head/block.

Glen

**yoshimitsu9** · 28-05-2009, 01:15 PM

Originally Posted by feral4mr2

is a new set of leads too. i might order a new coil and see how that goes, seems wierd to do it on 2 coils i have. plus i'll try the other igniter i have.
i'll turn the lights off in the shed next time, i was doing it last night and just used my body to block out the light.

thanks

dont automatically assume just because they are spanking news leads they arent faulty.

a bloke i know spent around $2000 replacing parts on his vt commonwhore because it wasnt runnning right, after all that it ended up being brand new faulty spark plug leads causing him all the issues.