Hi, my 54 plate vectra sri cdti 120 has all of a sudden gone really **** on the fuel, i watch the range going down mile by mile as im driving along it will drop about 10 miles for every mile i drive, and i got about 150 miles to half a tank, thats driving it responsibly aswell lol. If im on the motorway at 70 mph the range will climb, but as soon as i start driving at round town speeds it drops off rapidly. No eml is on and no codes stored in ecu. Any ideas?