How long can I drive before repairing cylinder 4 misfiring? on 1996 Mazda MPV

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Check engine light diagnostic indicates cylinder 4 misfiring. Mechanic says I can drive a while longer, but it will get rougher. Light went out on it's own, but has come back on 2 weeks later - same diagnostic. Cost estimated at $300 to repair. I cannot afford this at the moment and may be given another vehicle in the next couple of weeks. How long/far can I drive the car at this point before giving up?
(1) Answer
If you do not repair a misfiring cylinder, and we're talking spark plug, coil, wire or the like -- then you are risking serious engine and catalytic converter damage that will cost you many times more than the $300 you were quoted.

If the misfire is spark related - which is what it sounds like -- then unburnt fuel is still being sent to the cylinder and out your exhaust - causing your catalytic converter to get entirely too hot - and causing damage.