Focus - instant fuel economy display?

[pugdriver]

Hi

I'm looking at buying a new a Focus TDCI.

I would like the car to have instantaneous fuel economy display in the trip computer.. The owners manual says it does. I have looked at several cars and none of them do. They have average fuel consumption but not instant.

I have asked salesmen and they all assure me that it will, but none can show me a car with working instant fuel economy display.

I have looked at this and other online forums, it seems some people have this display in their Focus and others don't.

The most plausible explanation I have seen was on a UK Ford forum where there was a post saying that the service department can turn the feature on through IDS. (the integrated diagnostic system.) That poster said they need to "release INSTMPG on the BC." Whatever that is.

Has anybody had that done successfully?

Any service techs care to comment?

Thanks.