As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT, UPON START ATTEMPT FOR LH / #1 ENG LH ENG VALVE DISCREET + LT ILLUM, DUCT PRESSURE RETURNS TO 0 PSI. AIRCRAFT RETURNED TO BLOCKS (BTB). PUT THE APU BLEED AIR SWITCH TO THE OFF POSITION PER ABX 767 MPM 36-11-04. OPS CHECKED GOOD IAW 71-00-00. AIRCRAFT RETURNED TO SERVICE.