Reset your fuel average, fill up your tank to full until the fuel gun auto stops,check air pressure in tyres 33psi, reset trip meter, drive on motorway, refuel again until gun auto stops, then divide kms on trip meter by litres of fuel refueled. and keep speed between 100/110. I get almost 17 using these things on khi/ hyd motorway. But direction of wind also matters as when travelling back to karachi from Hyderabad wind is in opposite direction hence avg decreases to almost 13/14