Does stop smoke really work for engine - 1994 Ford Crown Victoria

It might, for a while. Unfortunately, these are temporary measures that are not repairs, but are cover-ups for the more serious issue that hasn't been addressed. In some cases, these products can actually do more harm than good, as they are designed to plug up leaks from small gaps. Sometimes they plug the wrong gaps and cause other problems. The real solution is to properly repair the problem. If that is not feasible or you are trying to nurse a dying horse a short while longer, than weight the benefits versus the risks and roll the dice, and hope for a good result. I, personally, would not use such products in my own vehicles.