[urq] Why misfire burns rotor?

[Maurits Jonkergouw]

Yesterday I was accelerating from 120 to 150 km/h in the Coupe GT (non urq content, sorry) when u huge misfire occurred. Now the second new rotor is burned after the last repair when my wife was having the same problems driving the car and came to a complete stop (see picture from link).

Could you please look at the pic and tell me what is most likely causing misfires in general and why is it burning the rotor like this? The previous rotor was even more burned and the HT terminal from the lead on the cap side (to the coil) came off too (melted). 

Also checked the (new) plugs and they look like they've been very hot (clean and white, no deposits). So I think it's running lean (wrong CO), but I'm not 100% sure. Perhaps the NKG BP6ES plugs I using now (and the previous ones) are just not correct, although they are the official cross-reference for the Bosch W6DC plug.

Thanks in advance.


http://www.moregraphics.nl/quattro/images/burned_rotor.jpg