What was found
ON APPROACH, WHITE SMOKE CABIN & COCKPIT. RAN QRH , DID NOT DETERMINE SOURCE OF SMOKE. BORESCOPED LT ENG 1ST STAGE HPC & 4TH STAGE HPC, NO DEFECTS IAW EMM 72-00-00. PERFORMED ENG CONSUMPTION RUN, ENG RAN APPROX 1 HOUR, NO DEFECTS, SMOKE, OR ODORS IAW EMM 71-00-00. BORESCOPED RT ENG, 1ST STAGE HPC & 4TH STAGE HPC IAW EMM 72-00-00. DURING ENG RUN, RT ENG OIL LEVEL FLUCTUATING. R & R OIL PUMP. INSTALLED ORIGINAL REPAIRED AGB & PERFORMED ENG RUNS & LEAK CHECKS, NO DEFECTS IAW EMM 71-00-00, 72-60-01, AND 79-20-05. MX FOUND AN AIR RESTRICTION ORIFICE IN APU BLEED LINES, BROKEN PIECE OF ORIFICE WENT DOWNSTREAM & RESTED ON ACM HEAT EXCHANGER. R & R DAMAGED APU BLEED LINE & REMOVED DEBRIS FROM EXCHANGER.