AH astra 1.8L code (p0303)

[Timsim9000]

Wont be the phaser problem then. A fuel pump problem wouldn't be related to a misfire in #3.
You replaced the plugs with new ones? New coil pack?
Disconnect the harness plug to #3 injector, with a multimeter check the resistance of the injector. There should be some resistance. An open circuit would mean the injector is fubar'd.

Thanks mate, Whats within spec of good resistance?

 

[lmoengnr]

Thanks mate, Whats within spec of good resistance?

Somewhere between 5-20 ohms.
Might want to check all 4 injectors as a comparison.