Call around some local brake shops and talk to the guys and see if they will help you out it doesn't take 5 minutes to run through the procedure.not saying it will fix it considering i cant look at it in person but there known to trap air in them.
May as well be traped gas lol.. Good thinking about calling around. I do have someone in mind now that you brought it up..
If the pedal is good and hard without the engine running and not so good running, those large boosters are also known for making it "feel" like it's going to the floor when in reality, it is just doing what it's supposed to, give you maximum brake pressure. A good example is a 98-up Econoline, if you push the pedal down hard with the engine running, it feels like it bottoms the master like you have no pedal, turn it off and bleed off the booster and it's hard as a rock.
Ok so, today was a waste but not totally. We bought a used ABS unit. $45 was not bad for a gamble. Put it on and the same low pedal.. This time the ABS light was on tho. I took it back off and put his origional back on and the light is now off. We bought a shop manual from fleabay so he says he will wait to see what it might say if anything. Now he wants me to check his daytime running lights. They come on when they feel like it lol. Hopefully the manual will help in these areas..
And the lights were working fine before you starting messing with the brakes...right? Geez! Poor dad!