What was found
AFTER ENGINE START AND WELL AFTER APU SHUTDOWN CABIN FILLED WITH A LIGHT FOG OF SMOKE. REMOVED APU. INSPECTED FIREWALL, MOUNTS, AND SUPPORT STRUCTURE. NO DEFECTS FOUND. INSTALLED REPAIRED APU IAW CE-750 M/M 49-10-00 AND HONEYWELL GTCP36-150CX MM 49-20-00. OPS AND LEAK CHECK IS GOOD. REMOVED P/N : 3800576-1 , REMOVED S/N : P-412, INSTALLED P/N : 3800576-1 , INSTALLED S/N : P-166.