As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IMMEDIATELY UPON ROTATION, ALL F/A STATION AND COCKPIT SMELLED A VERY ACRID, HEAVY ODOR. APU WAS OFF A/C FLIGHT RETURNED TO LAND THERE WAS NO SMOKE PRESENT. MTC IN PROGRESS. FOUND LT ENGINE AS SOURCE OF ODOR. REMOVED AND REPLACED NR 1 PER TRANSMITTAL. CHECKS GOOD OK FOR SERVICE. RUN UP CK ALL GOOD.