Pinking under load?

[sjb]

On the journey home after picking up my new CSL I noticed that when in a low gear (probably too low a gear-I was taking it easy) there is a 'pink' or 'pinging' depending on how you say it. It only does it for a second and at a certain load I guess. It only happens when I probably should be in one gear higher and when there's a load on the engine like a hill. No matter if I should be in another gear it obviously shouldn't be doing this anyway....even if it is slight and very brief, I can remember my Dad's old cortina 2000E pinking all the way up hills it's not like that. The seller put a quarter of a tank of fuel in so I initially thought he may have put supermarket crap in there so brimmed it with v-power and it's made a difference, does the ecu have ro re-adjust to different octane fuels over time? a long shot I know

What should I do next? I'm taking it easy and not loading the engine now anyway and keeping the revs up so I don't get it. It would be nice if it was something simple like plugs or the coil but I think it's going to have to plugged in and diagnosed???

It does a rather comprehensive 6 month warranty but it would be s shame if I have to go that route already.

Cheers in advance, Shawn.