Have a misfire code on cylinder 3 tried sparkplug wires and was told injector .

The problem has to be found before it can be fixed and that requires 'hands-on' testing ! .. A 'qualified mechanic' using a professional scanner, a fuel pressure & vacuum test gauge, can determine exactly what is causing the misfire .. That's the least expensive route to take and will insure a successful repair. .. It seems someone has already tried guessing at it and that can be expensive while not actually helping .. e.g. catalytic converter replacement.