backfire has 4 distinct synonyms spread across 3 of its 7 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a loud noise made by the explosion of fuel in the manifold or exhaust of an internal combustion engine
a fire that is set intentionally in order to slow an approaching forest fire or grassfire by clearing a burned area in its path
emit a loud noise as a result of undergoing a backfire
“My old car backfires all the time”
set a controlled fire to halt an advancing forest to prairie fire
Synonyms, antonyms and the broader and narrower relations for backfire come from Princeton University’s WordNet. Full sources and licences.