My Ford Duratec knocks on the lower octane. So whenever I can I use high octane but the local garages have dropped it, so Tesco is the only local supplier.
It is interesting that the ignition advances on the better fuel perhaps that's why it knocks when I fill it with the ordinary stuff.
It will take time to revert back to a lower octane fuel, they sometimes say a tank or two so might knock until then.. not ideal.
