What was found
DURING APU START WHILE SITTING AT THE GATE IN YUL, THE APU OVERTEMPED AND SHUTDOWN. SMOKE ENTERED THE CABIN THROUGH THE ENVIRONMENTAL CONTROL SYSTEM. THE FLIGHT CREW CALLED FOR CFR AND DEPLANED THE PASSENGERS. CFR FOUND NO INDICATION OF FIRE. THE APU WAS DEFERRED AND THE AIRCRAFT RELEASED FOR FLIGHT. MAINTENANCE TROUBLESHOT THE APU AT MSP. THE APU WAS INSPECTED AND OPS CHECKED NORMAL. IT IS BELIEVED THAT AN INCOMPLETE APU START CAUSED THE SMOKE.