I had the same issue but after the pump and the injectors everything was A okOriginally posted by Immo
I had to upgrade my fuelpump (also have gt-s injectors).
My fuelpump couldn't deliver, especially when boost kicked in, so I was running mad lean (1:19 !!) and in higher rpms it got a bit better (1:15) but still too lean. upgraded fuelpump and all was fine.