With an EFI engine the first thing is codes!
The pdf I linked to will show you how to diagnose each code or each circut of the EFI system.
One mecahical thing this EFI can't do is read or change fuel pressure, it expects it to be correct and since you have a fueling issue you should check fuel pressure. If your return line is plugged or somhow restricted it will raise fuel pressure sometimes doubling!!!