Does anyone know what the official fuel quality is supposed to be like?

Do all brands come from the same source?

Reason. We have been looking at buying a new Hyundai. They do not do any diesel models as the diesel quality is so poor it causes problems with the engines.

A friend has just had an engine failure on a Ford caused by poor diesel fuel, and apparently Audi will not honour warrenty claims which can be attributed to poor diesel.

Any info appreciated.

Colin