u/RabidBlackSquirrel

1999 3.0 v6, The saga continues. It's been nearly two years now since my first post: https://www.reddit.com/r/fordranger/comments/1hvyybr/missing_cylinder_for_15_seconds_on_cold_start/

I'd since gone through and replaced all ignition bits:https://www.reddit.com/r/fordranger/comments/1sdl3v3/whats_up_with_this_cylinder/

Plugs, wires, coil, IAC, MAF, PCV, all replaced, all OEM parts. Misfire actually went away for a couple weeks but has now returned. It rarely throws a code but when it does, always cylinder 6 and cylinder 6 only. It always goes away within ~15 seconds. Truck drives great, no miss no stumbles no issues. Warm starts are perfect. No smoke of any kind.

So... what now? I need to run a compression test for my own sanity, but wouldn't low compression lead to other running issues that I don't have?

• Bad injector? She's on original injectors at 130k miles. OEM injectors on these don't seem to be failure prone though.

• Valve stem seal? Could there be some oil leaking through when I shut the truck down that coats the plug overnight and burns off when I go to start later?

If it was on of the above two, why would it go away after an ignition refresh and then come back? New plug a bit more resilient to fouling initially being that it was all squeaky clean and new?

• Something else? That vertical scoring I saw in my scope was a little worrying.