What was found
DEN - FLT 655 - NR 4 ENGINE, 2 PERCENT LOW N1 AT TAKEOFF AT 882 DEGREES, TARGET 92.5, ACTUAL 90.5 PERCENT N1. UNABLE TO DUPLICATE, NR 4 ENGINE CHECKED AT 871C AT RATED TAKEOFF. REMOVED AND REPLACED NR 4 FCU PER BANDOCH (PRECAUTIONARY) RESISTANCE CHECK OK. BLEED BAND ACT OK, PLUGGED OFF CUSTOMER BLEED PORT, POPPET VALVE CHECK, BLEED BAND DURING RUN, NO CHANGE.