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Old 04-25-2012, 04:33 PM   #1
JohnM10
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Default Worn out Denso IK16 Plugs

Here are some pictures of my Denso Iridium Power IK16 spark plugs after 33,500 miles. I was shocked to see 2 of the electrodes completely burned. Is this normal wear for Iridium plugs?
I replaced them with the same plugs as I had already ordered them online but I think I will go with NGK Platinum plugs next time.



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Old 04-25-2012, 05:39 PM   #2
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Did you gap these plugs? This is usually what happens when someone measures the gap with incorrect tools. The iridium breaks off, and the plugs wear just like this.

I'm not familiar with Denso gaskets, but if this were an NGK plug, I would tell you that you did not torque the plugs tight enough either. Use a torque wrench, or turn the plug 1/2 to 2/3 of a turn after finger tight (FOR A NEW PLUG ONLY). Used plug is about 1/12 of a turn.
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Old 04-25-2012, 05:41 PM   #3
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BTW, Denso is NGK's closest competitor in terms of quality and technology.
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Old 04-27-2012, 02:53 PM   #4
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Did you gap these plugs? This is usually what happens when someone measures the gap with incorrect tools. The iridium breaks off, and the plugs wear just like this.

I'm not familiar with Denso gaskets, but if this were an NGK plug, I would tell you that you did not torque the plugs tight enough either. Use a torque wrench, or turn the plug 1/2 to 2/3 of a turn after finger tight (FOR A NEW PLUG ONLY). Used plug is about 1/12 of a turn.

That was my first experience with Iridium plugs and after pulling them out of the box I didn't even attempt to gap them as I was afraid of damaging them. That was also my first time changing the plugs in my Impreza and there was no way my 1/2 drive torque wrench was going to fit in there. If anything I probably over-torqued them as I didn't want them too loose.
I have since bought a 3/8 drive torque wrench and used it to torque the new set of plugs this time, although the torque wrench was still a little to long to do this accurately

Coming from a Honda Prelude and my wife's Nissan Altima, replacing the plugs on the Impreza is a chore.
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Old 04-27-2012, 02:57 PM   #5
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BTW, Denso is NGK's closest competitor in terms of quality and technology.
I choose them after reading the big spark plug FAQ. I hope these come out looking better than the last ones.
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Old 04-27-2012, 03:20 PM   #6
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That was my first experience with Iridium plugs and after pulling them out of the box I didn't even attempt to gap them as I was afraid of damaging them. That was also my first time changing the plugs in my Impreza and there was no way my 1/2 drive torque wrench was going to fit in there. If anything I probably over-torqued them as I didn't want them too loose.
I have since bought a 3/8 drive torque wrench and used it to torque the new set of plugs this time, although the torque wrench was still a little to long to do this accurately

Coming from a Honda Prelude and my wife's Nissan Altima, replacing the plugs on the Impreza is a chore.
Do the angular method. Remember that once the plug is tight, you have a little ways to go until the gasket is crushed properly. You will feel the plug tighten as the gasket touches the head. Once you keep going, you will feel it tighten again as the gasket is crushed.

I don't know what happened with your plugs, but this is exactly what it looks like when the iridium is broken off. If all 4 plugs looked the same, I'd say they were in too long, but since two are good and two are bad, chances are something damaged those plugs before they made it into your engine.

It is possible that Denso skimped out on the amount of iridium, but again if that was the case, all 4 plugs would be fairly equal.

Can you take a really close picture of the two plugs that are still looking ok? I'd like to see how much iridium is left.
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Old 04-27-2012, 09:11 PM   #7
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Old 04-27-2012, 09:50 PM   #8
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I know that sometimes people will buy plugs.....and return them.....once they figure out that they ****ed them up

I worked at advance auto and actually had guys bring me back Ir plugs that they knew they ****ed up, back....because I LOOKED at the plugs when I sold them to the guy and they were ok....they were toast when he brought them back....even after I TOLD the guy that he was gonna **** them up when he bought the WRONG kind of gap tool....

he told him to take them back to another store 'cuz i wasnt gonna take them back

that may have been what happened
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Old 04-28-2012, 05:39 PM   #9
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I ordered them online from Amazon but they could have certainly been damaged prior to me me receiving them. I will probably never know. I am surprised however that the engine was not running really bad with 2 of the plugs with the gap that big.
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Old 04-30-2012, 08:40 AM   #10
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How about the other one, one the "good" ones? I'm more interested in that one since it still has Iridium left.
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Old 04-30-2012, 08:54 AM   #11
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Originally Posted by JohnM10 View Post
I ordered them online from Amazon but they could have certainly been damaged prior to me me receiving them. I will probably never know. I am surprised however that the engine was not running really bad with 2 of the plugs with the gap that big.
At a certain point, the plug is no longer sparking across the gap, spark is actually going down the white ceramic of the center electrode. We call this internal flashover, or side spark. Some engines can run ok with this condition, but it's not the most efficient. Other cars will misfire like crazy.

It can wear out the coils by overheating them, so you don't want this condition to continue.
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Old 04-30-2012, 06:51 PM   #12
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close up pic 2:


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Old 04-30-2012, 06:52 PM   #13
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sorry, duplicate post, please disregard...

Last edited by JohnM10; 04-30-2012 at 07:00 PM.
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Old 05-01-2012, 10:05 AM   #14
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Quote:
Originally Posted by JohnM10 View Post
close up pic 2:
There is a lot of iridium left on this plug. This would lead me to conclude that the other two plugs had some serious wear issues. Two things it could be, those cylinders are causing a ton of extra wear, or the iridium was broken off somehow. Most likely, the iridium was broken off somehow. Double check the next plugs you put in to make sure the iridium is there. Also, just be extra careful when handling them.

One more question: This engine is coil on plug (COP), right? In other words, there is one coil per plug, and it's not a wasted spark type setup? AFAIK, everything post like 2000 is COP, but I just want to make sure.
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Old 05-01-2012, 01:09 PM   #15
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There is one coil\ igniter assembly that the 4 plug wires go into. Unless there is 4 seperate coils in this assembly then it isn't a COP on my 2006 SOHC.

it looks like this:
http://www.autopartswarehouse.com/de...QQSIUF538.html
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Old 05-01-2012, 01:36 PM   #16
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Oh really!? I didn't know subaru was using this setup. I'm pretty sure this is a waste spark system. (I'm very familiar with this ignition system, but never knew it was used at Subaru). It means that two plugs fire at the same time, so each plug fires in between the compression and power stroke, and again in between the exhaust and intake stroke.

For more info:

What this means is that one plug in the circuit will wear the center electrode, and the other will wear the ground electrode. This explains why two of your plugs have center electrode wear, and the other two have ground electrode wear.

The good news is, the plugs were likely not damaged when they went in. The bad news is, that the plugs will wear faster since they are sparking twice as often as other vehicles.

So what can you do? Well, not too much, unfortunately. You might have better luck with a different Denso part number or even NGK plugs. I can't tell you which ones since I don't know the amount of iridium in our (NGK) aftermarket plugs. You might try to call the NGK hotline and tell them that you have a wasted spark system, and you want a plug with more iridium in the center electrode. They may or may not be able to help you, I've never had occasion to ask them about this. (I work in NGK's technical center, so I deal more with testing the product rather than what we actually offer)

The other thing you could to to save a buck, is take the two used plugs with good center electrodes and move them to the cylinders that had the worn plugs in them, and put two new plugs in the other two. Sort of like rotating your tires. If the extra cost of the plugs isn't a big deal to you, put 4 new ones in.

Ultimately, you will want to stick with the plug that Subaru recommends, as that should be the plug that will last the longest (this isn't always true, but it's a good bet).

This system that subaru is using in this engine isn't the best for spark plug service life, but it's cheaper to manufacture.
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Old 05-01-2012, 02:35 PM   #17
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Thanks for the good info. I think I will be changing this new set out after ~$15k instead of 30k and will go with the NGK Platinum plugs next time. At about $7 per plug I won't be going through the trouble of swapping them between cylinders. I would do it on my wife's Nissan Altima but not my Subaru; too much of a pain.
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Old 05-18-2013, 08:46 PM   #18
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Well I went with the Denso Iridium Power IK16 spark plugs again at 83K and I just changed the plugs while I was doing a timing belt change at 102K. This is a picture of the plugs after ~ 20K miles.

http://imageshack.us/photo/my-images/254/im000530.jpg/



The iridium element on both cylinder 3 & 4 plugs were almost gone.

I replaced them this time with NGK Laser Platinum FR5AP-11 plugs and hope that they hold up better.

Last edited by JohnM10; 05-20-2013 at 10:59 PM.
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Old 05-18-2013, 10:12 PM   #19
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Quote:
Originally Posted by JohnM10 View Post
Well I went with the Denso Iridium Power IK16 spark plugs again at 83K and I just changed the plugs while I was doing a timing belt change at 102K. This is a picture of the plugs after ~ 20K miles.

http://imageshack.us/photo/my-images/254/im000530.jpg/

The iridium element on both cylinder 3 & 4 plugs were almost gone.

I replaced them this time with NGK Laser Platinum FR5AP-11 plugs and hope that they hold up better.

i took 40k mile denso platnium TT plugs outta my car not long ago...coulda re-gapped them and put them back in for another 20k

they cost me $8......for all 4
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Old 05-18-2013, 10:16 PM   #20
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FR5AP-11 has too big of a gap. You will get less life out of them. They have a 1.1mm gap. Turbo engines should have 0.8mm gap.
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Old 05-18-2013, 10:17 PM   #21
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Quote:
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FR5AP-11 has too big of a gap. You will get less life out of them. They have a 1.1mm gap. Turbo engines should have 0.8mm gap.

i think he's got a 2.5i
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Old 05-18-2013, 10:19 PM   #22
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Quote:
Originally Posted by Uncle Scotty View Post

i think he's got a 2.5i
Oh, I'm on the mobile app, can't see profile. Isn't that a waste spark setup?


Edit: I should look at my own post above... :P Anyway, yea waste spark automatically means the plugs will last half as long.

Last edited by Bacon117; 05-18-2013 at 11:20 PM.
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Old 05-19-2013, 08:58 AM   #23
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This coil pack has 4 secondary outputs for the spark plug wires. The ECU
fires for each cylinder only on the compression stroke. It doesn't fire between the intake and exhaust strokes.

I had a Honda motorcycle (4 stroke), 50 years ago, that used one set of points. It had 2 cylinders and fired the plugs every time the piston came up. The NGK copper plugs would only go 4500 miles.

Quote:
Originally Posted by Bacon117 View Post
Oh really!? I didn't know subaru was using this setup. I'm pretty sure this is a waste spark system. (I'm very familiar with this ignition system, but never knew it was used at Subaru). It means that two plugs fire at the same time, so each plug fires in between the compression and power stroke, and again in between the exhaust and intake stroke.

For more info: Wasted spark - Wikipedia, the free encyclopedia

What this means is that one plug in the circuit will wear the center electrode, and the other will wear the ground electrode. This explains why two of your plugs have center electrode wear, and the other two have ground electrode wear.

The good news is, the plugs were likely not damaged when they went in. The bad news is, that the plugs will wear faster since they are sparking twice as often as other vehicles.

So what can you do? Well, not too much, unfortunately. You might have better luck with a different Denso part number or even NGK plugs. I can't tell you which ones since I don't know the amount of iridium in our (NGK) aftermarket plugs. You might try to call the NGK hotline and tell them that you have a wasted spark system, and you want a plug with more iridium in the center electrode. They may or may not be able to help you, I've never had occasion to ask them about this. (I work in NGK's technical center, so I deal more with testing the product rather than what we actually offer)

The other thing you could to to save a buck, is take the two used plugs with good center electrodes and move them to the cylinders that had the worn plugs in them, and put two new plugs in the other two. Sort of like rotating your tires. If the extra cost of the plugs isn't a big deal to you, put 4 new ones in.

Ultimately, you will want to stick with the plug that Subaru recommends, as that should be the plug that will last the longest (this isn't always true, but it's a good bet).

This system that subaru is using in this engine isn't the best for spark plug service life, but it's cheaper to manufacture.
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Old 05-19-2013, 11:02 AM   #24
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Quote:
Originally Posted by CRAZYHAWK View Post
This coil pack has 4 secondary outputs for the spark plug wires. The ECU
fires for each cylinder only on the compression stroke. It doesn't fire between the intake and exhaust strokes.

I had a Honda motorcycle (4 stroke), 50 years ago, that used one set of points. It had 2 cylinders and fired the plugs every time the piston came up. The NGK copper plugs would only go 4500 miles.
You either need 4 separate coils or a distributor. The coil pack OP linked looks like 2 separate coils, which is waste spark. No, I have never worked with this exact coil, but I have worked with waste spark systems at Ford as recent as 2008. Waste spark is old and fading technology, but it's still around.

Also, the plugs he posted were 100% from a waste spark system. 2 plugs had wear on the center electrode while 2 had wear on the ground. This is because 2 plugs are on the same circuit, one is positive polarity (wears the ground electrode), and the other is negative polarity (wears the center electrode). This, I have no doubt. So, either the OP posted plugs from a different engine, or the 2.5i is a waste spark setup.
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Old 05-19-2013, 11:16 AM   #25
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Anyone have the wiring diagram for the 2.5i ignition system?
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