As specific car brand has same engine specification, so getting good or bad mileage is not the engine fault. Car always consume max petrol when you press ur accelerator, because max fuel is required to make the car move or increasing speed, otherwise a little fuel is enough to keep the car moving. So it all depend on how much speed breakers u have in local travel. I have 2 ways to go to my office, one has just 4 speed breakers whilst other has 22, so i got 11 km/l and 7.5 km/l average respectively on these 2 ways, as engine is same, so its all the acceleration which consume fuel