how to bypass the anti theft on a 2001 explorer

Do you mean the car will not start or the engine will not turn over (spin) when the key is turned. Merely changing the engine should not affect the anti-theft settings. Does the fob cycle the doors? Cycle it a few times with the doors closed then give it a try.

I last the key whit thebchip i have one whit no chip

The anti-theft system