I won,t go into tech details but I was told by someone in the fuel industry that there is at best minimum testing of fuel ron quality ie meeting standards and levels stated . He claimed only one company regularly tested the fuel others rarely did , this would explain why my T5 petrol van reacts to different companies fuel .If I run one companies fuel the van is fine then I fill from another company same RON and I get an engine warning light strange that one . The light goes out if filled from the other company again .