Did you check the connection?
If you have a technician stethoscope, you can hear it clicking. If you don't have one... 3$ at Harbor freight!
Could be a piece of dirt that entered the injector and plugged it.
Since it's not a completely close system (there's flow), no need to bleed the air, it's pushed out in a few seconds.
When the connection is in tight places, one of the connector pins can be pushed out a bit because there's no room to push it dead straight, and make bad contact. I'll check that first.
Make sure that it's the cylinder on which you remove the injector than is not firing, coincidence can happen
