95 civic, brake pedal sinks when the car is running. Will build up pressure when the car is off after a few pumps of the pedal.
What could be wrong, have bled all calipers and even the master cylinder
Thanks in advance for the help.

 

Bad master cylinder would be my guess. With vacuum assist, it's too much pressure for the weak MC to handle and sinks to the floor, but not quite fully blown out so will build pressure without vacuum assist.

 

It looks like its brand new when I bought the car, maybe installed wrong

 

Previous owner likely didn't bench bleed the MC prior to install.