94 honda accord with no break pressure?

Car had no break pressure. No brake fluid leaks. Bled the breaks thinking that would solve the problem it didn't. Replaced master cylinder (not remaned) brand new. Re-beld breaks now the pedal has tons of pressure and acts normal with out the engine running but while the engine is running the pedal goes right to the floor with minimal breaking. I don't know what to do.

Is this one of those brake systems that split the master cylinder side to side (RF+LR LF+RR) rather them front and rear? If so your bleeding may need to be done again. Also if this car has drum brakes on the rear you need to make sure the brakes are adjusted correctly. The brake booster is working just fine don't go buying one. Does the pedal pump up when running, that would be brake adjust problem and I think that is where you need to work.

1. Leaky brake booster line.
2. Brake booster need to be replace.

Booster problem…

If you didn't bench bleed the master cylinder you may need to get a pressure bleeder to get all the air out. Try bleeding diagonally as suggested but plan on doing it a few times.

Do you hear an air leak when pressing the break? Sounds like the booster is bad

Dittos to what others have said… Here is an unlikely, obscure cause - but it happened to me: new car… Took it in for service… Unknowing mechanic put standard brake fluid in it which reacted with the factory silicone fluid… Which made the brake hoses swell shut inside. This was only discovered after all calipers, wheel cylinders, master cylinder & booster were replaced.