Do you know if the injectors where replaced to address this fault or if the fault has come about since the replacement?
Is it possible to check rail pressure with a manual gauge and maybe monitor pressure sensor output voltage at the same time just in the case that the switch circuit is maybe shorted/open.
It's not something I have tried but would it be possible to disconnect individual injectors and test as before only on 3 cylinders, just in case one injector is sticking open.
A mechanic I know used to put a small ball bearing in the injector feed pipe to block fuel flow and run them on three cylinders until he eliminated each one.