A B737-300 WAS DISPATCHED AFTER EXTENSIVE TROUBLESHOOTING; REPAIR AND REPLACEMENT OF UNITS FOR A CHRONIC #2 ENG FIRE WARNING. APPROX 1 HR INTO FLT; ACFT DIVERTED DUE TO #2 ENG FALSE FIRE WARNING.

Narrative

MAR/XA/00; ACFT XYZ RETURNED TO ZZZ WITH AN OVERHEAT LIGHT ON 'A' LOOP #2 ENG. 'B' LOOP WAS DEFERRED. WE TROUBLESHOT 'B' LOOP ISOLATING TO CONNECTOR #2906 PER WIRE DIAGRAM MANUAL. ISOLATED SHORT THAT DISAPPEARED WHEN CONNECTOR REMOVED. REPLACED CONNECTOR AND LOWER FIRE 'B' LOOP PRECAUTIONARY. 'B' SYS TESTED NORMAL PER MAINT MANUAL. REPLACED FIRE DETECTOR ACCESSORY UNIT AND TESTED PER MAINT MANUAL TO CORRECT 'A' SYS OVERHEAT LIGHT. BOTH SYS NORMAL; NO DEFERRALS. CALLBACK CONVERSATION WITH RPTR ACN 464751 REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT WAS WORKED FOR A CHRONIC #2 FIRE WARNING 'A' AND 'B' LOOP. THE RPTR SAID THE 'A' LOOP WAS CORRECTED WITH A DETECTOR UNIT REPLACEMENT AND TESTED PER THE MAINT MANUAL. THE RPTR SAID 'B' LOOP WAS FOUND TO HAVE A SHORTED CONNECTED AND WAS REPLACED AND ALSO REPLACED THE LOWER FIRE SENSING LOOP ON THE 'B' SYS. THE RPTR STATED THE ENG WAS RUN AT HIGH PWR (90%) FOR 15 MINS AND BOTH SYS OPERATED OK. THE RPTR SAID THE AIRPLANE WAS RETURNED TO SVC AND DISPATCHED AND AFTER 1 HR OF FLT DIVERTED DUE TO #2 ENG FIRE WARNING. THE RPTR SAID THE RPTED FIX WAS ALL FIRE SENSING LOOPS WERE REPLACED ON #2 ENG.