Guess what guys my guy has a nice 89 deville in real good shape with a broke transmission, and the car is only 300 dollers i will buy it. I know how the 4.9 and 4.5 engines are suppossed to be interchangable. Well I got a 4.9 with the transmission so my question is this: Will my 4.9 engine with the transmission fit right in without any mods? Do I need to change the computer too? what all would i need?
This is definitely not a plug and play swap. Your 89 Deville came equipped with a 4T60 non electronic transmission while the transmission matted to the 4.9 is a 4T60E electronic transmission. As a result, the transmission on the 4.9 will not shift with the computer in your 89 Deville. The computer on your 89 as well as wiring is different than a car with a 4.9 engine. You have a couple of choices though to make it work.
1. Get a donor car with the 4.9 and change over all the wiring and computers so that it'll work with the 4.9 and 4T60E transmission.
2. Swap the 4T60 non electronic valve body with the 4T60E transmission. I have never heard of this being done but I don't see why it would not work. They are basically the same transmission but different valve bodies. You could use either the 4.5 engine or 4.9 engine with this setup.
3. Rebuild your 4T60 transmission and use the 4.9 engine. You would have to use the intake manifold and TBI off your 4.5. You'll also need to add an adjustable FPR to get the extra fuel requirements of the larger engine dialed in.
Hope that you are mechanically inclined if you do choose to do any of these choices.