What was found
DURING CLIMBOUT EXPERIENCED SLUGGISH ENGINE RESPONSE NR 4 ENGINE AT FL 210. CLIMBING THROUGH FL 290 HEARD AUDIBLE STALL AND OBSERVED SUBSEQUENT TOTAL LOSS OF ENGINE POWER. ALL PARAMETERS DROPPED OFF INCLUDING EGT. RELIGHT OF ENGINE WAS NORMAL AND ENGINE PERFORMANCE REMAINED NORMAL DURING RETURN TO JFK. INSPECTED INLET/EXHAUST AND BLEEDS, BORESCOPED ENGINE 8TH, 9TH, 14TH, AND 15TH STAGE COMPRESSORS, BORESCOPED 1ST AND 2ND STAGE TURBINES, NO DAMAGE. REMOVED AND REPLACED FUEL CONTROL UNIT AND TT2 SENSOR.