Engine swaps

Is a 1994 Cadillac DeVille engine interchangable with a 2001 Cadillac DeVille?

I’m sure there are major changes in the engine control and fuel injection systems, so they aren’t interchangeable.

If the engine size is the same and will fit on the mounts ok, then you can swap them. However, the electrical work needed will be the biggest problem. The wiring harnesses are most likely different and you’ll have to find some way of splicing the old and new harnesses together. This is where you’ll run into tons of problems that will not make it worth your while to do it.

…and the ECM will have to be swapped, along with the engine.

However, whether the wiring harness of a '94 DeVille can even accomodate the ECM of an '01 DeVille is another question that the OP needs to resolve before sinking any money into this project.

Unfortunately, this is not like swapping a '51 Merc engine into a '40 Ford.

Are they both NorthStars?? If so, 1994 would have been the first year they used that engine in the DeVille… But even if they were both NorthStars, it would cost more than the car is worth to swap engines… The electronic interface turns into a nightmare few can deal with…If emissions testing is required, it’s completely impossible…