Great post!

I have a Daihatsu Copen with the same error codes, P0300/1/2/3/4 and have been trying to get the bottom of it for weeks.

Replaced injectors, vacuum hoses, plugs etc. But still no joy.

The only way to access the fuel pump and filter is by taking the whole tank out and it is a big job. No issues starting in the morning though and no power loss. I am going to replace the coils next.

Good luck!