What was found
TAXIING TO RW27L, TAXIIED INTO POSITION, ANOTHER AIRCRAFT STATED OVER THE RADIO, (IT LOOKS LIKE FIRE COMING OUT OF THE APU EXHAUST), DECIDED TO TAXI DOWN THE RUNWAY AND TURN OFF THE APU. NO FIRE INDICATIONS WERE NOTED IN THE COCKPIT UNTIL I SET THE BRAKE AND PARKED, THEN GET AN APU FORE FAIL MSG, FOLLOWED BY AN APU FIRE WARNING. CALLED FOR THE IAC AND BLEW THE APU FIRE BOTTLE, FIRE INDICATIONS WENT AWAY. AT THAT POINT FIRE TRUCKS ARRIVED AND WE OPENED THE DOOR . FIREMAN STILL SAW SMOKE FROM THE APU SO WER EVACUATED THE AIRCRAFT. (K) REMOVED AND REPLACED APU IAW CRJ AMM 49-10-00. OPS AND LEAK CHECK GOOD. (M)