I have a 2000 Disco II, 150k miles. I have changed plugs and wires ( Bosch/Magnecor) about 1 year ago. I keep getting P0307 codes...cyl 7 misfire...I pulled the plug, the tip was rust colored, with no fouling that I could see. I put in a new plug, cleared the code, and it ran about 50 miles before throwing the same code. I have checked to make sure the plug wire is seated on the coil and the plug, which it is, Please help, I don't really know what to do here...

 

All i know is that could mean bad things for your wallet as it did for me. Lots of potential problems there, maybe a bad headgasket, maybe a weak coil, bad plug wire or plug, or in my case a rod that was bent and then let go in catastrophic fashion. Maybe someone else can help you find exactly what the problem is.

 

Pull that plug out, reattach the plug wire and run the engine in the dark, does it spark nice and strong?
Does coolant come out of the plug hole?
Are you loosing any coolant?

 

Are the other plugs still clean? Just because there is a misfire code on that one cylinder doesn't mean you shouldn't take a quick peek at all of them. If the others are clean you have wasted nothing but a few min of time. If they all look like that this quickly it is an additional clue.