Faulty firecracker (3)
I believe the answer is:
dud
'faulty firecracker' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for dud that I've seen before include "Forged" , "A palindromic washout" , "'Flop, turkey (3)'" , "Failure; washout" , "Fake -- failure" .)