Mweinst

I pulled my spark plugs after running them for about 500 miles. One of the plugs has a dark spot on the side of the insulator. It only is on about 1/4 of the ceramic. The old plug from that cylinder had the same spot on it. Take a look and let me know if I should be concerned.

I know that the picture isn't that clear.

Auto_Werks 3.6

i noticed that on a set of plugs that i ran for only a hundred miles or so. I don't have an actual answer but i assume it has something to do with the direction of flame propagation making a shadow, but its a wild guess. strange that one cylinder is different in yours though, i had several like that

Mweinst

The fact that it's only on one plug is what made me make this post. That, and because the same spot was on the old plug, as well. Something's definitely going on in that cylinder to create that spot. I just don't know if it's okay, or if I need to be aware of some problem. I spent some time on Google, but couldn't find anything just like it.

grumpyf14d

Well, you can certainly see where the fuel air mixture is igniting. Timing looks ok considering where the mark is on the strap. If anything it looks like a little rich in that cylinder. What does the top of the piston look like?

Mweinst

I'm not 100% sure because it was hard to see in, but it looked a little moist on the top of the piston. Besides that, it looked pretty clean.