What was found
AIRCRAFT APU RUNNING ON GROUND / CABIN FILLED UP WITH BLUE SMOKE, CUT APU BLEED AIR OFF, AND SMOKE SLOWED BUT DID NOT STOP, AIRCRAFT HAD BEEN SITTING IN HEAVY RAIN. STARTED BOTH ENGINES, AC DID NOT SMOKE. FOUND APU OIL OVERSERVICED. REMOVED EXCESS OIL, RAN APU . OPS CHECK GOOD. NO SMOKE W/ APU BLEED AIR. WORK PERFORMED IAW HONEYWELL RE-100(XL) APU MM CHAP 49-90-00 .