If you have access to an occiliscope you can check the signal from the ECU at the injector plugs and also direct from the ECU.

In theory you could also do this with a test lamp (a proper bulb test lamp, not one of those shit LED test lamps that MAC Tools make!! Usless peices of shit).

Connect the croc clip to the positive battery terminal and probe the negative connection on the injector plug. If it pulses on and off when the car is running, it is getting a signal from the ECU. If not, you can do this at the ECU end of the wiring loom and see if it work there.

If it works at the ECU plug but not at the injector plug, then there is a wiring fault.

Assuming it's a Cossie, wiring pin numbers and colours for the injectors are as follows...

Cylinder 1 - Pin 18 Brown/yellow trace
Cylinder 2 - Pin 32 Brown/green trace
Cylinder 3 - Pin 33 Brown/black trace
Cylinder 4 - Pin 35 Brown/white trace