What was found
APU STARTED NORMALLY ON THE GND BUT SHUT ITSELF OFF AFTER 2 MINUTES OF NORMAL OPERATION. OBSERVED & SMELLED WHITE SMOKE FROM THE WEMACS AS THE UNIT SHUT DOWN. THE APU FAIL LIGHT WAS ALSO ILLUMINATED. DOWNLOADED ECU -3 SHUTDOWN HISTORY HAS FAULT NR 4 LOW OIL PRESS SWITCH INPUT & NR 15 NO ENG SPEED SENSED. OIL VISIBLE ON INTAKE & DRAIN LINES. REMOVED APU PN 3800722-1, SN P-313, BUILT-UP & INSTALLED REPLACEMENT APU PN 3800722-1, SN P-570 IAW MM 49-10-00. SERVICED APU OIL IAW MM 12-11-03 WITH BP2380. RAN APU, OPERATIONS & LEAK CHECKED GOOD.