What was found
NR 1 ENGINE N1 INDICATION BECAME UNSTABLE DURING CLIMB. REPEAT WRITE-UP. THEN EGT EXCEEDED LIMITS AT 952 DEG THEN FUEL FLOW INDICATION BECAME UNSTABLE WITH SURGING AND YAW. PULLED TO IDLE N-1 AND FF INDICATION REMAINED UNSTABLE BUT SURGING STOPPED. PERFORMED FADEC BITE TEST AND PULLED FAULT CODES NOTHING ABNORMAL FOUND. BORESCOPED HPT STAGE 1 AND 2 PER 72-00-00-6. NO DEFECTS NOTED. REMOVED AND REPLACED HMU REF AMM 73-13-00-4. PERFORMED PWR RUN PER JRH, ALL PARAMETERS WERE WITHIN LIMITS PER JRH.