As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT, NOTICED NH GAUGE FLUCTUATING RAPIDLY +/- 10 PERCENT. REDUCED POWER AND SELECTED NR 1 EEC TO MANUAL. NH GAUGE STILL FLUCTUATED. ALL OTHER ENGINE PARAMETERS NORMAL. INSTALLED NH SENSOR FOR TROUBLESHOOTING. DURING ENGINE RUNS NH/NL (LT) START FLUCTUATING AT GROUND IDLE. SWAPPED GAUGES. PROBLEM FOLLOWED. INSTALLED SERVICEABLE NH/NL GAUGE (LT). RAN ENGINES. OPS CHECK GOOD. P/N: SEDL-0C29M, S/N ON: 174A, S/N OFF: 180.