actually, all EFIs cant use advancers. it basically depends on what kind of ignition system ur car uses. i dont know abt city, but if ur car has a distributor, then chances are that u cant use an advancer. even if ur CNG technicial tells u dont believe him. ur car will continue knocking if u want good pickup and speed while running CNG. thats the trouble with CNG, u cant have the best of both CNG and petrol at the same time