As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DIAGNOSTICS REPORTS NR 1 ENGINE TREND DATA SHOWS A SHIFT IN DELTA CRUISE AND TAKEOFF MARGIN INDICATIVE OF EGT INDICATION ERRORS. ACFT GROUNDED. ACCOMPLISHED TSR, REF MM 77-21-01 FOUND THE T49.5 S4 EGT PROBE OUT OF LIMITS, REPLACED S4 PROBE REF MM 77-21-01, OPS CK GOOD REF MM 73-21-00-700-804-F00.