For a while now I've had a miss on startup that clears within 10-20 seconds, which new leads hasn't sorted, so I figured/hoped a new set of plugs would sort that when I got around to it, or at worst one of my britpart coil packs was failing. This might still be an entirely unrelated problem, however..
Over the last couple of days I've had a missfire that rapidly got worse, to the point cyl 6 died entirely on my way home from work. Same on LPG and petrol. Plug lead connected fine at both ends, and it was only cyl 6 that was dead and not also a cylinder on the other bank, suggesting investigating the plug end first was the way to go. Pulled the plug... and it looked like this:
These plugs were new in 18 months ago, maybe slightly longer... so while they could do with changing, this looks concerning. I pulled another out and it looked like your typical wear - nothing unusual. #6 though looks like it has been rusting away...
I'm not losing coolant (for once), no steam other than when its humid out and the box has the usual condensation in it. Even if it were coolant, it wouldn't rust, and it should look clean rather than stained I would have thought. So lets say it was straight water in the cooling system, the plug would have to be sat in it to do that.
To further confuse things, when I did a compression test last year, this cylinder had higher compression than the rest - considerably higher if I recall. I didn't have my tester with me last night, just one that was older than me, which read about 150-180 psi but the non-return valve was leaking so didn't see a proper figure. I was mostly interested to see if I'd lost compression entirely at the time on that cylinder.
So I'm not sure what to make of this... conveniently had a spare plug from a Honda engined generator that fit, and its now running on all 8 again as if nothing had happened. Too early to tell on the startup miss, there seems to be little consistency as to when it does that, apart from cold startup.