I have a 03 Odyssey that has a break pedal that when you are driving it goes all the way to the floor. If you pump it again, you get a good pedal. I thought it was the master cylinder but I replaced it and there was no improvement. Here are some of the symptoms:

• When driving first push of the brake pedal goes to the floor, the next one is good.
• I checked and there is good vacuum coming from the manifold to the booster pump.
• With the car off, if you pump the brakes you get better pedal each time you pump the pedal, but when you start the car it goes straight to the floor.
• With the car running, the first time I hit the pedal it goes all the way to the floor.
• With the engine running, if press-and-hold the brake pedal, then turn the engine off. Nothing happens to the pedal height

Any help or guidance would be greatly appreciated.

Thanks, Brian