As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN PACKS TURNED ON AFTER T/O, COCKPIT FILLED WITH ACIDIC, SWEET FUMES. ISOLATED PACKS AND BLEED AIR VALVES, WAS UNABLE TO ISOLATE SOURCE. RETURNED TO FIELD. FOUND ENGINE EVC OUT OF TRIM. TRIMMED PER 747MM 71-00-00 TEST 8, PG 580C GROUND RAN FOR 1.5 HOURS WITH NO FURTHER SMOKE OR FUMES NOTED.