A misfire in your car means that there's incomplete combustion within the engine. In short, one of your engine's cylinders isn't firing at all or was firing, but not thoroughly. Usually, misfires only impact one cylinder. But, if the situation worsens, you might experience misfires in numerous cylinders at once. You'll notice a misfire when the engine feels and sounds rough, as one (or more) cylinders isn't firing in unison with the rest. Moreover, other tell-tale signs that your engine is misfiring include poor performance or hesitation while accelerating. You might notice how it loses power momentarily, or that the engine shakes and rattles more pronouncedly. Leave it unfixed, and you'll soon notice other long-term symptoms appearing, such as bad fuel economy and increased emissions.