Brakes on 1999 S-10 pickup four-wheel-drive
with the engine not running the brake pedal is very hard to push. As soon as I start the engine the brake pedal goes to the floor and will not pump up. I have replaced all the lines, bled all the wheels, replace the master cylinder all to no avail. Vacuum booster seems to be working okay. Any help you could give me would be greatly appreciated. Thank you