Problems After Engine Change.

I have changed engine from a (4 cyl) 2.4 to a (6 cyl) 3.8 engine. and now it will not start. it starts up briefly and die again.
I have a feeling it is the immobilizer who makes trouble. is there anyone who knows if the immobilizer and the ECU to be coded together. ??

Greeting Per

Car 98 Voyager 2,4 aut with immobilizer and chip in the key
Doner car 96 3,8 Aut with No immobilizer and No chip in the key