I have a 1997 XE Hardbody 4cyl, 4wd, 5spd, standard cab. The brake pedal goes to the floor only while the engine is running. When I turn the engine off the pedal goes back to normal. I checked the vacuum hose for leaks and it seems ok, the master cylinder is just over a year old also. Does anyone have an idea on what would cause this? Thanks

 

Vaccuum leak or the brake booster I would guess.

 

Possible air in the line... try flushing it or get the air out of the lines like you do when you replace a caliper mine did the same thing and i fixed it

 

did you bleed brake master and the brake booster? if you did check brake hoses see if they move when pushing pedal down if it has rear brake drums see if wheel cylinders are leaking rear shoes could be out of adjustment.

 

I would suggest you to check the brake booster might be that has gone wrong. so do check and let us know.

 

Go head and check the brake booster. i think that might have gone faulty why don't you replace and check with that.

 

Vacuum leak that could be one of then. remove them and wash and clean them and later try to connect.

Nissan Altima Tail Lights

 

most of the time its vacuum leak and I always ask for assistance whenever I got that problem it didn't cost that much asking for pro help.

 

"The brake pedal touches the floor" problems due to so many reason either one listed below could cause the problem .
- Leak in the braking system
- Low brake fluid level in the brake fluid reservoir
- Air or water particles in the brake fluid (it requires brake bleeding)
- Leak in the brake master cylinder
- Worn out brake pads
- Vacuum problem in the brake power booster
- Leak in either brake circuit
- Improper brake adjustment
for the further information in the braking problem related solution you are cordially invited to visit my blog. Fixation of brake problems