As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAXI OUT WHILE STARTING LEFT HAND ENGINE START VALVE DID NOT OPEN ,LEFT STARTER EICAS MESSAGE APEARED. AC RETURNED TO THE GATE AND MTX GROUNDED AC AND DEFERRED LH START VALVE FOR DEPATURE IAW MEL ABX-80-00-2-1.AND RETURNED AC TO SERVICE.