What was found
REPEAT WRITE UP - NO RAIN, NO ANTI ICING DONE, NOTHING BUT CLEAR WX PRECEEDING THIS EVENT. ON TAXI OUT NEARLY 2 TO 3 MINUTES AFTER ENG START WE RECEIVED A MIN EQUIP SMOKE WARNING STEADY FOR APPROX 30 SECONDS. NO SMOKE WAS DETECTED IN THE F/O'S SNIFFER. APU WAS DEFERRED AND NOT USED FOR ENG START. SUSPECT OIL CONTAMINATION INTO AIR CONDITIONING DUCTS. REF TSM 26-15-00 FIG 102, BOTH WATER SEPARATOR COALESCER BAGS R&R IAW AMM 21-51-16-03. NEED TO CARRY OUT AIR CONDITIONING DUCT CLEANING PROCEDURE REF AMM 21-51-00-03 USING ENGINE AIR. AIR CONDITIONING DUCTS CLEANING PROCEDURE PER MM 21-51-00-03, ENGINE RUN PERFORMED BY CREW, NO MORE SMOKE NOR ALERT.