Will a 2004 dodge neon engine work in a 2001 dodge neon?
No, The neon was revamped in 2003, with updated engines and chassis changes. As a Chrysler mechanic, the 2000 dodge neon 2.4L DOHC is the best. That will fit in a 2001 also.
The most simple explaination is that there is no real difference. Plymouth was the original company that both Dodge and Chrysler grew out of offically in 2001. The 2001 Plymouth Neon was the last car the Plymouth produced so really there is not many differences at all between a 2001 Plymouth Neon and a 2002 Dodge Neon.