As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING L ENG START WHEN STARTER MOVED TO "GND" DUCT PRESS DROPPED TO ALMOST NOTHING, N2 NEVER SPOOLED UP TO MORE THAN 15%. DUCT PRESS WAS 30 PSI PRIOR TO THIS.(<P>SWAPPED ECU WITH KNOWN GOOD PART, OPS CHECK BAD. RETURNED AIRCRAFT TO ORIGINAL CONFIG. TRANSFERRED TO MDDR #128556, CAT 'C', DUE 29MAY20. MCC NOTIFIED. PLACARDS INSTALLED. DDG 49-11-01-01. YK @ 13:46. APU PNEUMATICS INOP.</P>)