Spark Plug Analysis

[Legacy777]

In reference to this thread
http://bbs.legacycentral.org/viewtopic.php?t=36987

I swapped out my spark plugs. They looked pretty good, not really much wear. I think they only had about 5000 miles on them. Gap was around 1.1 mm, so the higher end of the gap spec. But the interesting thing was the wear color. They all looked to have more or less normal wear color, but the passenger rear plug, cylinder 3 had more of a black/sooty color then the other three, which were a little lighter.

The interesting thing about this is that cylinder 3 is at the end of the fuel rail, and supposedly has more of a chance to run lean. The color I saw would indicate the opposite to me.

I took some pictures, however all but one didn't show up. I'll try and take some more today.

[Legacy777]

Here's pics
http://www.main.experiencetherave.com/s ... ngkplugs2/

[Legacy777]

bumpage

[entirelyturbo]

Is that soot, or is it oil? On the threads especially, it almost looks a bit oily to me.

Hey, it could be the other situation and you could be leaning out #3 as you said, since it is indeed last in line.

I assume your A/F is stoich for the most part?

[93forestpearl]

Maybe its me but those plugs look decently worn. The edges of the electrode look rounded.


I don't know what to tell you about the darker plug.

[Legacy777]

It's soot. Any oily type looking stuff is left over anti-seize. It's definitely not oil.

If I'm leaning out #3 why would it have a darker looking plug? That's the only thing that's confusing. The fact the color is the same on all three except that cylinder. I like uniformity in my engine.

A/F ratios are stioch for normal cruise and what not. They are rich under boost, or at least they were the last time I checked. This graph is pretty indicative of what I saw with my wide band

http://www.main.experiencetherave.com/s ... gdyno2.jpg

[Legacy777]

Maybe its me but those plugs look decently worn. The edges of the electrode look rounded.


I don't know what to tell you about the darker plug.

I do see what you mean Dan. They aren't sharp edged any more.....and that was less then 5,000 miles of use.


Hmmm any other thoughts on the darker plug?

[93forestpearl]

Are you on stock boost? I was getting 2-3k miles out of 7's gapped at .028. I run a little more than stock boost though, lol.


Maybe its related to your misfire issue. If you weren't getting a good burn in that cylinder, it could leave soot.

[Legacy777]

More or less. I was running around 10 psi. Granted I was using a MBC.

Maybe it's related to the slight misfire.

I guess while we're on the plug issue....do you think going to the 7's would be recommended once I get this thing tuned?

[93forestpearl]

I'm not sure. The WRX uses 6's stock, right? That's at 1 bar.


I'm not a plug master by any means. IIRC, too hot of plugs can lead to detonation? What I've always been told by tuners is only go as cold as you have to and run the largest gap you can get away with.

[BXSS]

They all look a little lean, but # 4 looks the worse of all of the plugs - it is the whitest.
+
The little white pimples/specs are pieces of metal that were melted & blown off the electrode.

I used a Motorcycle spark plug reading guide which aims for a Brown Color when playing with my cars & the Old School Puerto Rican Drag racers I know aim for the same color -
I could have just asked them, but that would have been too easy.

I have a 14 month old NGK from cyl #4 out of my OBS-t that has decent color laying around the house somewhere.
I'm too dumb to post a pic, but I can take a pic & e-mail it to someone to post over here.

[Legacy777]

Thanks for the comments, and any other spark plug gurus feel free to comment.

Yeah email the pic. I'll post it.

[Imprezive]

I would suggest a compression & leak down test, to rule out blow by or anything like that and to make sure you are getting optimum ignition conditions

[Legacy777]

Motor barely has 5000 miles on it since rebuild....so I'm a little less included I have those issues. Not saying I don't.....but a little less included to believe that I have an issue.

[NICO]

i just did my spark plugs to day and my plugs look like that every time i take them out.

i run the 7s and gap is all ways at 25, i could open them up to 28, but when they ware out !!i will no right away with all the missing going on, so 25 gives me a extra bit of time.

also try indexing the spark plugs i do it all the time, point the spark plugs open section to the ex valves and the tab to the intake valves.

[Legacy777]

New wires.....didn't seem to change anything.

Started a new thread here
http://bbs.legacycentral.org/viewtopic.php?t=37117

[SemperGuard]

Those plugs look fine. They don't look as though they would cause any drivability issues. I think you're making a mountain out of a molehill.

[Legacy777]

It's very possible I am

[93Leg-c]

I thought this NGK reference guide was interesting, though it's a bit old. http://www.dansmc.com/Spark_Plugs/Spark ... talog.html

My ss and TW aren't modified like yours but all my plugs have a light tan color to them except for cylinders #4 which are running a bit hot. Plugs #1-3 in my engines are like the pic #16.

On one NA engine and one turbo engine, my number 4 plugs were a bit whiter than yours. Both engines died because of cylinders 4 running excessively hot.

As BXSS mentioned, your #4 plug is whiter than the rest. You might want to watch that cylinder.

[Legacy777]

Thanks for the link.

#4 cylinder is going to be getting the slightly higher flowing injector....so that may help that cylinder out.