Dont know if the link below the text will work to the PDF but Top Tier realizes that standards may need to change due to the explosion of DFI engines.
Gasoline Plus Standards
TOP TIER™+ Gasoline Performance Standard
The TOP TIER™+ Gasoline Performance Standard will extend the current benefits to newer, higher-efficiency gasoline direct-injected (GDI) engines. The new Plus gasoline standard will include a GDI Fuel Injector Cleanliness Engine Dynamometer Test while monitoring for optimal emissions and combustion behavior.Gasoline Plus Standards