So I changed my spark plugs after 110k. The procedure went fine. The only thing is that i noticed the rightmost plug has a layer of brown deposit. The other plugs looked fine. See picture. Any clues? Thx.
Yes number 4 cyl spark plug well was full of water at some point. Common problem that usually results in misfire of that cyl because the water shorts out the igniter. Caused by failure of gasket on water dam right above the head in the valley below the windshield. I would imagine the igniter spark plug boot is corroded also. Or very over zealous carwashing. And....interested in the wear on the electrode area please. Could you post another picture of that too? And there's alot of rust on the threaded area of all the plugs. I hope you used this on the new plugs: http://www.permatex.com/products/au...ts/Permatex_Copper_Anti-Seize_Lubricant_b.htm And filled the igniter boots with dielectric grease.
Hard to say without knowing the plug gap. The spec is 1.0-1.1 mm. I agree that cyl 4 spark plug well had water in it. I assume that the corresponding igniter also had a rust stain? I'm surprised that the OP's car did not log DTC P0304.
I'm pretty sure the thread pitch is 1.25mm, so yeah the gap is not too far off. Yep it's pretty amazing jut how little electrode wear there is considering they've done 110 kmiles. I'd put new ones in after going to all the trouble to take them out etc, but I have to admit that they do look like they could be cleaned up re-gapped and tossed back in for another 110 kmiles!
It is not recommended that used iridium spark plugs should be regapped. The reason is that the side electrode might break off and end up in the combustion chamber where it can cause significant mischief.
