brake problems, help please!!
 

hey guys general question about brakes here. my brakes wont seem to stiffen up when i bled them and they seem to want to go all the way to floor, rather the engine is off or on. I have no fluid leaks anywhere and i have been over every last inch of brake line so i know this much 4 sure no external leaks at all. So my question,,,is there a way to tell rather its the brake master cylinder or the RABS valve 4 sure that is causeing this problem? this is a 91 explorer XLT 4wd with rear anti lock brakes not true ABS. another thing is i have replaced the brake master cylinderall the calipers, wheel cylinders,brakes lines both metal and rubber,and all new hardware. The only thing not changed so far is the RABS valve or proportioning valve im not certain which its actually called but that is the part im suspecious of. I have the instrument panelout at the moment but last time i checked the rear anti lock brake light was on i would assume there is a way to check for codes on the brake system but this i am also uncertain of or how to do it. If anyone has info on this type of brake system as far as how to retreive brake system codes or has a good idea of what is wrong with my brakes id really appreciate the help!! I have always been more into working on the engine in a car so when it comes to brakes im still a rookie for the most part..