hi mate if youve got over 300 bhp and have an uprated walbro pump fitted?if so for the car to run propely you need a minimum of half a tank but more so a full tank as the walbro pump empties the tiny poxy swirl pot that ford fitted to the car faster than it can fill so try filling the car full of petrol then see if car runs propely as i had this problem with mine and car is perfect if i have full tank but misfires below half a tank.hope this helps you mate!