What was found
AIRCRAFT WAS GROUNDED: OIL SMELL WAS DETECTED AT GATE SHORTLY AFTER PACKS WERE TURNED ON WITH THE APU POWERING THE BLEEDS. THE ODOR WENT AWAY QUICKLY.ON TAXI OUT WITH THE ENGINES POWERING BOTH PACKS THE SMELL CAMEBACK BUT WAS FAINT. DURING TAKEOFF ROLL AND INITIAL CLIMB THE SMELL CAME BACK AND WAS VERY STRONG, LASTING APPROXIMATELY 5-MINUTES. THE SMELL WAS NOT DETECTED BY THE FLIGHT ATTENDANTS AND WAS LOCALIZED TO THE FLIGHT DECK. REF: 7610202 MAINTENANCE FOUND DUCT AT ACM SPLIT AND REPLACED REMOVED AND REPLACED LH ACM MIX MUFFLER DUCT IAW AMM 21-51-17