leehardy3

hey all,
i have just returned from driving my B6 S4 across France and spain. on the way back it started a serious misfire, so bad in fact i had to leave it in france and get it recovered. i have just been told that 1 Cat has failed and the spark plugs are red suggesting wrong fuel. i use 95ron in the uk which is recommended on the fuel filler cap, it also says that 97ron is good. in both france and Spain it is either 95ron/E10 or 98ron. i chose the 95/E10 but did put 1 tank of 98ron into it on the way down to spain. i probably used another 5 tanks before i started to get any problems. has anyone had any such issues or knows if either of the fuels i put through would cause this damage. fortunately a compression test has come back good so no internal damage.
any insights gratefully received.