Help! Bleeding brakes 98 2WD Blazer!
 

So I just got done replacing my back two calipers and putting new rotors all the way around. My dad and I got the system bled out (or so we thought) with good pedal with the ignition off. However, as soon as the truck is fired up, I lose the pedal, it goes straight to the floor.

We have gone around and bled all four brakes several times, with no air coming out anymore. What am I missing here? The reservoir was completely emptied during the caliper exchange, and I've seen some people posting about air being trapped in the ABS system perhaps? Although all these threads never have a definitive fix for the problem. Any help (and pictures if possible!) on what's wrong or where to bleed the system would really be appreciated!

If the reservoir emptied then you need to bleed the master cylinder,and very possibly the abs pump. Im pretty sure there are steps here for the master cylinder. As for the abs pump if you need to bleed that they can be a real pain,since some you have to use a tech2 type scanner to make the abs pump purge itself.

So should I just break down and take it to the dealership to get it bleed out correctly? Or if I get one of these scanners can I do it myself? I'm just at a loss @ how I should go about rectifying this problem.

When the vehicle is running and you pump the pedal do you get the pressure back??

No, i can pump it all day and no pressure builds up w/ the ignition on. With ignition off it builds up fine.

When its on do you hear any noises like a vacuum leak or the abs pump running or anything different.

No, everything sounds the same, should I pull the vacum hose and make sure im getting pressure, could this be the problem?

like someone mentioned you may have to bleed the master cylinder. Are you losing any more fluid when you filled the resevoir?