Technical changes for 1975 included the addition of a catalytic converter and electronic ignition to not only meet the stringent 1975 and later emission requirements, but also extended routine maintenance intervals, and improved fuel economy and driveability which was a must in the era immediately following the 1973–74 energy crisis, but also spelled the end of dual exhaust systems and mandated the use of unleaded gasoline as the converter could be rendered useless if contaminated with lead.