Jesus said "before Abraham was I AM". To know what that meant to His contemporaries, look at the response from His hearers. Note the context at the end of verse 53. Then the response verse 59; the response of stoning is punishment for blasphemy, claiming to pre exist Abraham and using a reference to the omnipresent (I AM).
John 8: 53 Are you greater than our father Abraham, who died? And the prophets died! Who do you make yourself out to be?” 54 Jesus answered, “If I glorify myself, my glory is nothing. It is my Father who glorifies me, of whom you say, ‘He is our God.’[a] 55 But you have not known him. I know him. If I were to say that I do not know him, I would be a liar like you, but I do know him and I keep his word. 56 Your father Abraham rejoiced that he would see my day. He saw it and was glad.” 57 So the Jews said to him, “You are not yet fifty years old, and have you seen Abraham?” 58 Jesus said to them, “Truly, truly, I say to you, before Abraham was, I am.” 59 So they picked up stones to throw at him, but Jesus hid himself and went out of the temple.