What was found
UNUSUAL ODOR REPORTED BY FLIGHT ATTENDANT & CAPTAIN BEFORE BOARDING. SEEMED TO SUBSIDE, CALLED MAINT, NOTHING DESCOVERED. PUSHED BACK & STARTED ENGINES, NOW SMELLED AGAIN BY MULTIPLE CREW MEMBERS. SMELLED IS LIKE BURNING PLASTIC. DETERMINED TO BE TYPE 9 ODOR IAW W/C 0550-2002. C/W FIG 1-4, NO FAULTS NOTED. RAN & IS LOCATED ENG 1 & 2 BLEED W/. P TRACK TOOL & SUBMITED RESULTS TO MCC WAITING FURTHER EVAL. TALKED WITH MCC PERFROMED GVI OF BOTH ENG NR 1 & 2, PLUS APU, NO EVIDIENCE OF OIL LEAK OR COMTAMINATION C/W W/C 2100-2007, NO TROUBLE FOUND REMOVED AND REPLACED RECIRC FILTERS IAW AMM 21-21. PERFOMED P TRAC RUB IAW 2/C 0550-2001 RESULTS SIGNIFICANTLY LOWER THAN FIRST TEST. RAN P TRACK TEST AGAIN WITH ONLY ENG NR 1 RUNING PER MCC REQUEST TEST RESULTS CONTINUED TO TREND DOWN. ACFT OK FOR SVC. (LP: 9593462, AIRCRAFT WAS GROUNDED)