Episode #1.8 - S1-E8
Question: As we know Gene died in 1953 so how did he save Alex in 1981 from the car bomb, he was already dead and in the purgatory world?
Answer: Agree with the other answer. This is not the place for spoilers. I suggest checking the series' entry on Wikipedia. There is a synopsis of each season's episodes that may have the answer you seek. Check here: https://en.wikipedia.org/wiki/List_of_Ashes_to_Ashes_episodes.
Answer: Have you finished watching the entire series? I don't think it's fair to answer this for someone who hasn't.