I replaced my 2004 dodge durango engine with a 2001 dodge durango engine. Why won't it fire up?

my best guess is you put the 4.7l engine in your truck and did not swap over the correct timing gear like the crank and cam tone rings and is giving the computer an incorrect reading of when to create a firing event therefor no attempt at running. just fixed the same thing on a customer vehicle were he put the jtec version of the 4.7l in the ngc version of the durango and would not start/run. if thats the case the engine has to come back out.

first check the obviouse-the coil.then scan and see if the crank sensor is working,with 4,71 engine and the difference in the years theres alot that can be wrong,did you chenge the computer?