As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT RETURNED TO PLATFORM AS A CONSEQUENCE OF CAPTAIN REPORTED APU PNEUMATIC PRESSURE DOWN TO 8 PSI WHEN LEFT ENGINE STARTED INSULATION VALVE WAS OPENED. ENGINES WERE STARTED WITH A GPU AND REPORT WAS DEFERRED IAW MEL 49-11-01. DURING OVERNIGHT SERVICE, ECU WAS CHECKED AND IT HAD FAIL CODE OF IGV ACTUATOR. IT WAS REPLACED IAW MM 49-52-02, TESTED CORRECT.