Trying to help out a friend. He has a built 2.0 motor, and 1mm over size valves, 727cams. AEM EMS controlling a GT35, walbro 255fp, 850cc inj, Perrin Fuel Rail and AMS FPR kit, AMS intercooler + Pipes.
He went to get his car tuned today, and they said he was running lean at 5psi. They raised the pressure on the Regulator and tried again. Still no joy. 5psi= lean
He doesnt have a fuel pressure guage to know if his pressure is set, and doesnt have a WB (broken).

Would this be due to the injectors being to small for this setup, or a possibility of his fuel pump not working properly, or just the inital setup of his EMS? says he hasnt noticed the loud whine of the usual warlbro pump....
Im trying to figure this out for him because he is not 100% sure of how to work on his own ride, and im a fellow evo owner, with close to his same setup.(Stock blok for me and 1000cc injectors) and dont mind helping.

I told him it could either be the EMS, Fuel Pump, Injectors, or the Pressure Regulator. I also told him to reinstall his stock pressure regulator and see what happens. This will help with finding the problem. correct me if im wrong..
Thanks for the help in advance