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2009 OB 2.5i 4EAT
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Discussion Starter #1
Hey guys, got in the subie today and had a really uneven idle... every few seconds it would shake once or twice. Runs fine once accelerating. Got back in car on way home and my CEL came on, and looked under the hood to find arcing between the ignition coil and the 'high tension' cable/spark plug cord. I've attached an annotated image.. do I need a new wire??
 

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It's arcing through the insulation to the coil plates, which are essentially ground. Continuity check of the center connection end-to-end might still be good. The fault could be in the 90-degree bend to the coil tower. In any event, yes, the wire should be replaced. I'd get a new set of NGK wires (RC-FX101) -- if one wire's insulation is failing, the others are probably on the weak side as well.
 

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2009 OB 2.5i 4EAT
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Discussion Starter #4
It's arcing through the insulation to the coil plates, which are essentially ground. Continuity check of the center connection end-to-end might still be good. The fault could be in the 90-degree bend to the coil tower. In any event, yes, the wire should be replaced. I'd get a new set of NGK wires (RC-FX101) -- if one wire's insulation is failing, the others are probably on the weak side as well.
Alright, ordered a set. They're blue which is dope. Thanks for the recommendation. Checked the continuity on the cable and it was a null, so looks like it's indeed toast.

...Can I drive it without the cable on one plug?
 

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2012 OB , 2017 Impreza
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3,277 Posts
Plain OM is correct again.

What you are seeing is the typical failure-mode for ignition wires. You did 90% of the troubleshooting and now... just need to replace the ignition cables to correct the situation.

Incase you have never replaced ignition cables before. The most important rule is REPLACE ONE AT A TIME so you can route each new wire exactly like the originals to the proper sparkplug.

If you wish to do an even better job... get a small tube of silicone grease and rub a THIN layer on the inside of each of the rubber endcaps. This will help seal out the elements and ensure easy removal later when you need to change sparkplugs. One small tube of silicone grease should last you lifetime of re-assembling rubber and Oring seals.
 

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2014 OBW Premium (Ice Silver Metalic)
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"...Can I drive it without the cable on one plug?" You serious? You could, but I wouldn't recommend it.
 

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2009 OB 2.5i 4EAT
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Discussion Starter #7
"...Can I drive it without the cable on one plug?" You serious? You could, but I wouldn't recommend it.
Cables won't arrive till Sunday, so it's good to know if I can still drive it. I don't intend to go on a road trip, but if it doesn't cause permanent damage I'd like to retain my ability to do minor errands.
 

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2009 OB 2.5i 4EAT
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298 Posts
Discussion Starter #8
Incase you have never replaced ignition cables before. The most important rule is REPLACE ONE AT A TIME so you can route each new wire exactly like the originals to the proper sparkplug.
Good advice, I went through that yesterday replacing my PS hose and I was combing the internet for photos or video that happened to show where it was going.. not fun haha. I got some dielectric grease I can throw on the end caps.
 

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Cables won't arrive till Sunday, so it's good to know if I can still drive it. I don't intend to go on a road trip, but if it doesn't cause permanent damage I'd like to retain my ability to do minor errands.
It could cause permanent damage, including the cat converter, the engine, and the coil, even if not driven on the highway or for extended periods.
 

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2009 OB 2.5i 4EAT
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Discussion Starter #10
It could cause permanent damage, including the cat converter, the engine, and the coil, even if not driven on the highway or for extended periods.
Gotcha. Yeah I guess the unburnt fuel will burn the cats. I'll park it then. Back to being in highschool and being driven everywhere :grin2:
 

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Don't ignore the spark plugs and the connection to the spark plug.. As spark plugs age resistance increases and the voltage need to bridge the gap increases. With the increased voltage the spark plug wires are often the weakest link in the chain. With very few exceptions, I will change the plugs as well as the wires any time I see arching through the wires.
 

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'03 outback limited, '01 Outback Limited, '01 Legacy L wagon, '96 Legacy Brighton wagon
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Just go down to the local auto parts store and get any cable you can fit in properly to use as a temporary stop-gap measure until the NGK wires arrive. I even used some #4 welding cable once way back in college on a Datsun 1200 to replace the cooked high tension cable - it was just the right size to stuff into the coil and cap, held in place with a bunch of electrical tape. Got me through the remainder of a 1000 mile trip.
 
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