Did some testing on my brake booster using a vacuum gauge.

I did the FSM test on page 11-17
"POWER BRAKE UNIT ON-VEHICLE INSPECTION Method Using a Tester"

The picture is choppy but I installed a vacuum gauge in-line on the engine side connections. This is with the check valve installed.

The car would produce between 14-15 in-Hg at idle.

In both Unloaded and Loaded conditions the unit did not hold vacuum for 15 seconds. (it lost vacuum immediately when the engine was turned off)

This leads me to believe that the unit is not functioning.

 

Are you having a hard time stopping?

 

What was the original problem and what has lead you to the booster?

 

Recently replaced master cylinder.
Brake pedal goes to floor when the car is running.
However, the pedal feels normal when the car is off.

Previously, before the car was properly bled, the pedal would go to the floor regardless of on/off.

 

sounds like there is another problem. the booster should hold vacuum, so if it doesn't its bad. if it failed completely though the symptom is a hard pedal all the time.