I hehave a 99 ford taurus with brake issues,I've replaced the brake booster,master cyclender ,and bleeded the brakes.yet when car is off there is presuure in the brakes but when car is running there is no pressure and the pedal goes to the floor.PLEASE HELP

Sounds like you have air in the system. Did you bench bleed the master cylinder, prior to installation? Did you bleed the brakes in this order: RR, LF, LR, and RF? Did you tighten the lines going to the master cylinder with a flare or line wrench?

Sounds like you have air in the system. Did you bench bleed the master cylinder, prior to installation? Did you bleed the brakes in this order: RR, LF, LR, and RF? Did you tighten the lines going to the master cylinder with a flare or line wrench?

Yes I did all of that

Focus on the ABS system. Check for any ABS codes. Check all under hood and under dash fuses with a test light or multi-meter. Check your Owner's Manual for any ABS-related relays--if you find one, test it. Check connectors to the Hydraulic Control Unit.

Focus on the ABS system. Check for any ABS codes. Check all under hood and under dash fuses with a test light or multi-meter. Check your Owner's Manual for any ABS-related relays--if you find one, test it. Check connectors to the Hydraulic Control Unit.
Has no ABS on it and no leaks

Sounds like you have air in the system. Did you bench bleed the master cylinder, prior to installation? Did you bleed the brakes in this order: RR, LF, LR, and RF? Did you tighten the lines going to the master cylinder with a flare or line wrench?
There is a device that the vacuum line from the engine connects to that other lines connects to.it sits over top of master brake cylinder a small black box and supplys vaccuum also to brake booster.

Try adjusting the rear brake shoes and see if that helps. See if you disturbed the hoses going into the black box, which is likely a manifold.

Try adjusting the rear brake shoes and see if that helps. See if you disturbed the hoses going into the black box, which is likely a manifold.
There is a manifold at the rear of the car with brake lines going to it with a spring loaded lever I'm guessing it goes to the ABS system

First I need to ask if you bench bled the master before you installed it? If not, that is probably the problem you are having and the master could possibly be bad now. I know you said you did it but that is a big problem if you didn't. Also, TGM is correct in mentioning the bleeding order as that is very important. Be sure you did all of this.

If you did this and there are no leaks anywhere, you may need to have this pressure bled by someone. Years ago when I was a tech, we had a Taurus that wouldn't get a pedal after the calipers had been replaced. The ABS valve must have trapped air in it and no amount of normal bleeding would clear it. Once we got a pressure bleeder on it and went through that, the problem was cleared up.

Has no ABS on it and no leaks

ALL Ford Tauruses of that generation had ABS brakes.

Odinn7's idea of using a pressure bleeder is a great idea. The Cal-Van One-Man Brake Bleeder I use does the same thing. It has a one-way check valve in the end of it, which requires a fair amount of pressure on the pedal to bleed the fluid. This will ensure there is no entrapped air anywhere in the system. I've used it for 15 years on my 2000 DOHC Ford Taurus, with ABS brakes, and countless other brake/hydraulic clutch systems.