What was found
ENGINE BACKFIRE, POP DURING LANDING ROLL WITH ACCOMPANYING FLASH NOTICED FROM CABIN. NO ABNORMAL ENGINE INDICATIONS. *S/D* WHEN THE STALL IN REVERSE OCCURRED THE NR 4 ENGINE REVERSER WAS LOCKED AND DEACTIVATED SO IT WAS NOT USED FOR REVERSE AND COULD NOT HAVE STALLED IN REVERSE. HOWEVER, HNL ACCOMPLISHED STALL CHECKS ON ALL THE ENGINES NR 1, 2 AND 4 ENGINES CHECKED OK. NR 3 ENGINE FAILED THE RABS CHECK. FOUND THE RABS SWITCH FAULTY AND REPLACED SWITCH.