I have an 03 S type with 4.2L v8 that is bad .If i purchase a suitable replacement engine, how difficult is the swap ? My main concerns are with onboard computer and related electrical equipment, will that all work correctlly with a different motor . Will there have to be reprogramming done or some things along those lines that I possibly could not do myself. I have replaced several motors over the years but never a jag . I love the car. Any advice will be humbly appreciated and used.

 

The used engine won't normally come with computer (PCM) but simply keep the existing one anyway.

Make sure you buy the equivalent engine and then it's just a time-consuming job.

You'd do better to post in the right forum...

 

There are many threads about removing the 4.2 engines from the car in the S-type section of the forum. Do a search and some research to try to find the little idiosyncrasies and tricks to help disconnect the engine harnesses, hoses and accessories so the engine will cleanly lift out of the engine compartment. Things like the engine and trans does come out the top, but it is best if you remove the front bumper cover, and radiator assemblies, as well as the fender cover liners so you can reach things that need to be disconnected from the sides of the engine.

I dropped my first S-type engine out the bottom, the second I pulled out the top. Out the top is better overall. Plan on a full weekend to get the engine out. Probably take 8 to 12 hours total time to remove if all goes well. Also take lots of pictures and label/sort the parts as you take it apart. If you don't get the new engine put in within a week or two, you will forget where all the nuts and bolts go.

One of the problems you will run into is finding a good replacement engine. In my mind anything with over 75K miles should be refreshed before you put it in. For my 03 STR with a blown engine, I purchased an 04 STR replacment with 75k miles. I am still purchasing parts to do a partial rebuild on it.

High probability you will have to purchase a newer replacement engine (06 to 09 to find one that has under 100K miles. If you do, you will have to double check that all the bolt-on accessories and sensors are the same. You will want to use your original engine and trans harness. All of this isn't difficult, you just have to take a methodical approach to swapping parts if they are different.

Enjoy.