What was found
AFTER NR 1 ENG STARTED WITH APU ON TAXI TO RUNWAY WE SMELLED A STRONG BURNING SMELL. STARTED NR 2, IT WENT AWAY, SLIGHTLY CAME BACK WITH SAME BURNING SMELL. TROUBLE SHOT ODOR TO NR 1 PACK, DEFERRED 31 PACK, ACM MEL 21-27. COMPLIED WITH ETN-EM-72-034. TROUBLE SHOT USING ETN-EM-72-034(SEE LG PG 3819895 1, COULD NOT FIND ANY ABNORMAL SMELL AFTER RUNNING BOTH ENGS IAW RR 72-00-00. RAN NR 1 PACK, OPERATIONS CHECKED GOOD IAW AMM 21-51-00. MEL RESTORED.