Hello,I have not clear yet why sometimes I have read 'He pumped up the tire' and others 'He pumped the tire up'. Is it the same or what is the correct one?
Both are fine.
"Pump up" is a phrasal verb. Some phrasal verbs are 'separable' and some are not. That is, some phrasal verbs must have the verb and the preposition together (not separable) and some can go either way, either together or separated with the preposition at the end of the sentence (separable). Do a search on "phrasal verbs" and you will find lists of these. The list should also indicate whether each phrasal verb is separable or not.