Have you changed the injectors around to see if the fault persists on cylinder 4. I'm know expert but i'm fairly certain that amperage waveform isn't correct.

I've had issues in the past with the wiring from the main multi-plug (under inlet manifold) upto injectors and run new wires up to an injector before and soldered into the wiring loom.

That's though if i've got the correct system where the injector loom is in a rubber casing and forms 1 complete sub loom.