A fuel delivery system for a vehicle having an engine configured to selectively operate between a port fuel injection (PFI) mode, a gasoline direct injection (GDI) mode, and a port and direct fuel injection (PDI) mode. The fuel delivery system includes a PFI system including plurality of PFI injectors configured to supply fuel to the engine during the PFI mode, and a GDI system including a plurality of GDI injectors configured to supply fuel to the engine during the GDI mode. A fuel system monitor is configured to monitor the fuel delivery system when operating in the PFI mode, and attribute any fuel delivery system malfunctions occurring during the PFI mode to the PFI system alone, and monitor the fuel delivery system when operating in the GDI mode, and attribute any fuel delivery system malfunctions occurring during the GDI mode to the GDI system alone.