Dear Brother its not problem of CAT, i run alto 660cc from last 2 yrs upto 85000km, but i cant remove CAT and millage 19km on highway, 18km with A.C at the speed of 100-110km/hr, 15-16km in city. u just add injector cleaner in petrol tank and sometime use HOBC to clean injectors. use Liqui Moly ( germany) brand injector cleaner having price PKR 650/ , its sufficient for 75lit petrol.