Since my last update I've done a bit of testing.
Received my noid lights and went to test the signal, to see if the noid lights will light up. All of them did as well as saw that fuel was being pumped through the fuel lines. So no fault there.
Received all my parts with which I could test the injectors with. Took a while because the first signal generator didn't work with my injectors, so had to get a different one.
Tested each injector and all worked perfectly fine, even the 4th cylider one that had the fault code. Everything checks out.
Don't know what's left. Have to check the recently replaced swirl flaps? Will have to put the injectors back and maybe swap them around. Maybe something changes then but last time it didn't, so not sure.