What was found
PREFLIGHT FIRE DETECTION TEST, OVER HEAT, FIRE DETECTION LOOP "A", NR 2 ENGINE INOPERATIVE. ALSO SHOWS FAULT ON NR 2 WHEN LOOP "A" SELECTED. ACFT GROUNDED. INITIAL TEST NORMAL. RESISTANCE CHECKED D998 PIN 24 AND 25 AT ENGINE AND APU FIRE CONTROL MODULE SHOW 5 OHMS. AFTER OPENING ENGINE, RESISTANCE CHECK WENT TO 15 OHMS. TAPPED ON M1759 ENGINE CORE LT, RESISTANCE WENT OPEN. REPLACED M1759 ENGINE FIRE DETECTOR REF MM 26-11-01. REINSTALLED ENGINE & APU FIRE CONTROL MODULE. ENGINE FIRE TEST NORMAL.