What was found
WHILE SWITCHING FROM ENGINE BLEED TO APU BLEED IN PREPARATION FOR A BLEED OFF TAKEOFF, A THICK DARK SMOKE CAME OUT OF VENT SYS, PERFORMED APPROVED SMOKE IN COCKPIT/CABIN CHECK LIST. PERFORMED INSPECTION IAW AMM 05-51-26,FAULT WITH APU 49-94299, FAIL ATTEMPED START. RAN BOTH ENGS.AND PACKS, ISOLATION CLOSED NO BLEED OR PACK DISCREPANIES, REF L.P. 7280560/61 FOR APU PLACARD AND DIP TO REPLACE FILTERS. FAULT DATA FAULT CODE 1: 49-94299 FAULT COMMENTS : STARTER GENERATOR OIL FILTER SHOWS CLOGGED.