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Discussion Starter #1
Hey y'all. Changed the spark bangers in my gf's '06 Subaroo outback and I noticed something weird. I just bought her the car and therefore don't know the service history. I have attached a picture of the plugs, they're in numerical order from left to right. In the attachment you'll see that the spark plugs on the outside(cylinders 1&4) the electrode is worn down the the insulator where as the two on the inside are looking pretty decent and may still have about 15k of service life left. I've known lazy jiffy lube techs that would skip out on changing hard-to-reach spark plugs if they were in a hurry, but the cylinder 1 plug(left) is by far the easiest to change. The car has leaky valve cover tube seals and cylinders 1 & 4(the ones with the more worn out plugs) had more oil in them than cylinders 2&3. Would oil cause a higher resistance in the ignition circuit leading to shortened plug life? I just thought that I'd throw this out to you all here as food for thought. I know it has been interestimg for me, so perhaps the mechanically inclined and curious amogst you will aswell. It has all new ngk iridium plugs now and I'll have that tube seal problem fixed before long.
 

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Wow! I've had lots of cars and motorcycles over the years but have never seen plugs worn that much. The gap is looking like .060 on the last one. I would like to know the exact gap on that. As to the cause I wish I could help.How many miles are on them?
 

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Are they all iridium spark plugs???
100k mile spark plugs have iridium center electrode and a platinum button on the nickle ground electrode.
50k mile spark plugs have iridium center electrode and a nickle ground electrode.

Years ago NGK had problems with counterfeit spark plugs. I do not see it on their web site now.

From NGK:
Waste Spark Ignitions

Like most automotive systems, the ignition system has undergone many changes. One example is the Distributorless Ignition System, or “DIS” for short. This system was first introduced in the 1980s. The distributor, cap and rotor in a conventional system were replaced by coil packs. The new DIS system proved to be more reliable and required less maintenance.

The earliest DIS featured a bank of coils; one coil for every two cylinders. Each pair of coils would provide power to two spark plugs. Each of the two paired coils would fire the paired spark plugs simultaneously, one on the compression stroke and the other on the exhaust stroke. Since one plug is fired on the exhaust stroke, serving no real purpose, the system was known as a “waste spark system.” This style of ignition has negative and positive polarity sides to the coil; meaning the spark plug also has positive or negative polarity.

It is important to know that in a waste spark ignition, both the center firing electrode and ground electrode will see gap erosion. In plugs with a positive polarity, most wear will occur at the center-firing electrode. Plugs with negative polarity will experience more wear at the ground electrode. As a result of this, vehicles equipped with waste spark ignitions often use double precious metal spark plugs, such as the OE Iridium® or OE Platinum®. These dual precious metal plugs feature either iridium or platinum on the center-firing electrode and platinum at the ground electrode. Because these electrode materials are denser, gap erosion is reduced, allowing a longer service interval. Since these materials are denser, this will reduce gap erosion, thus leading to a much longer service interval. The use of nickel-alloy or single precious metal spark plugs in vehicles equipped with waste spark ignitions will result in more aggressive gap erosion and shorter spark plug life.
 

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definitely something wrong there
two got changed and the other two didnt??
i would put all new in and keep an eye on them.
 

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Either they are different plugs, or different ages, or quite possibly, someone tried to clean them (being the easy ones to get to) and not knowing what they were doing removed protective plating. I don't see any other way such a thing could happen
 

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my opinion.

based on burn pattern and electrode wear.... 2 has much less time in the engine.

as for Iridium plugs.... only way to go...

I have seen fleet cars with 150,000 miles on factory installed plugs look better then the best one in your photo.

to add to the point..
my VTX came with iridium plugs from the factory.. and at 89,000 miles, the plugs still look good.. and running FINE.
fyi.. the plugs has not needed a gap adjustment. I inspect them every 2 years.
 

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Discussion Starter #9
The performance isn't noticably better now but it does idle smoother

They are all the same plug, one has black lines from the oil burning on it(see leaking valve cover gasket)

They were all ngk double platinums with unknown milage.
 

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Discussion Starter #10
Wow! I've had lots of cars and motorcycles over the years but have never seen plugs worn that much. The gap is looking like .060 on the last one. I would like to know the exact gap on that. As to the cause I wish I could help.How many miles are on them?
I didn't check the gaps and have since thrown them out. Gaps did appear to be around .060 ±0.005 though
 
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