What was found
(CAN) WHILE STARTING THE ENGINES WITH INTENT TO PERFORM A TEST FLIGHT, FOLLOWING THE 500 HRS INSPECTION REQUIREMENTS, ON SELECTION OF BLEEDS TO MAX., A STRONG OIL ODOR WAS PRESENT. THE ACFT TAXIED WITH THE ODOR CONTINUING FOR A FURTHER 5 MINUTES. THE CREW TRIED TO ISOLATE THE SMELL BY SELECTING EACH BLEED ONE AT A TIME, WITH IT ONLY DISSIPATING WHEN BOTH BLEEDS WERE SELECTED OFF. WHEN BLEEDS WERE SELECTED ON, THE OIL SMELL RETURNED. TROUBLESHOOTING IS ON-GOING. MULTIPLE ENGINE RUNS WERE PERFORMED BY MAINTENANCE ENGINEER`S PRIOR TO THIS EVENT.