Focus LS Zetec 2006 strange performance problems

[StevenB]

Greetings, I am using 95 or 98 octane petrol since new and every time after servicing my car is sluggish. Return visit to Ford service centre cleared it in the past and Ford advised that they "reset the computer". Last service was not any different, expect that when I came back they told me that the resetting doesn't do anything and I am imagining things... I kept driving for about 4 months until I accidentally filled the tank with regular 91 unleaded. And instead of drop in performance, my car accelerated faster and had more torque up hills. It felt like "when it was good" on a 95 octane fuel. I could hear engine pinging (under hard acceleration and when pushing up hills), but the pinging stopped after few seconds. Yesterday I filled it up again with 95 octane and the car is definitely sluggish again with less power up hills... Can you assist with some ideas what can be wrong and more importantly, how to handle this with Ford ? BTW - I use Shell or BP only and car is now out of warranty. Thanks and regards, Steven