how could i check to see if the master cylanders bad?

Press the brake peddle down till it'* firm. Then hold it there. If your foot stays in one spot, it'* good, if it slowly goes down, then the master cylinder is leaking fluid past the seals.

well, thats exactly what it does all the time. so now i guess its the master cylander.

Sounds like it'* rebuild or replace. Not that hard of a job. You will need to bleed the brakes real good after your done.

and how do you bleed the brakes?

You can do it with 2 people, or by yourself with a brake bleeder. You need to open the bleeder valves, one wheel at a time. Then pump the brake until no more air is in that line. You will need to watch and make sure the master cylinder always has plenty of fluid in it. If it runs out you have to start over. Do this for each brake. If the peddle feels spongy, then you still have air in the brake lines.

back to the mileage issue....i don't get any better mileage than you do and i have done everything mentioned, from full tune up to MAF cleaning, O2 sensor etc, etc. I don't get why some of you guys double what i get with respect to mileage, it makes no sense to me and i always run 94 octane???

is there any possibility that the master cylander could give way completley and then i wont have any brakes at all?