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 TAKE-OFF MARGIN INDICATIVE OF EGT INDICATION ERRORS. ACFT GROUNDED. COMPLETED TSR 906574 IAW AMM 77-21-01-200-801-FOO. FOUND EGT PROBES S1 AND S4 OUT OF TOLERANCE. CLEANED S1 AND S4 EGT CONNECTIONS AND RE-RAN TEST. S1 VALUE WAS 58-40 AND S4 VALUE WAS 75.44.