What was found
DURING TAXI OUT, BOTH CREW MEMBERS NOTED LIGHT SMOKE FOLLOWED BY AN OIL ODOR. APU WAS SUPPLYING BLEED AIR FOR ECS AT THE TIME. APU WAS IMMEDIATELY SHUTDOWN, ECS SELECTED TO BOTH (ENGINES) POSITION ON PANEL CONDITIONS DID NOT IMPROVE. RETURNED TO RAMP, AND SHUTDOWN. NO EVIDENCE OF SOURCE WAS FOUND. INSPECTED APU INLET AND FOUND SIGNS OF BURNED OIL AROUND COMPRESSOR HUB. R & R APU IAW MM 49-00-00. OPS & LEAK CHECKED GOOD. RAN BOTH ENGINES AND APU, OIL ODOR IS NO LONGER PRESENT. REF MM 21-00-00.