98 - I am in the middle of the same swap (well, not middle...uh, first 1/4?)
Pirate4x4.com has a lot of good info. This forum has a few as well. I found few detailed write ups specifically on TJ 2.5 to 4.0 swaps - most were YJs. Here are a few tidbits I did learn
- Your T-case is 21 spline - you need to convert it to 23 spline, or buy a different T-case
- I think there were some electrical changes in 01 or so on the TJs - I suspect you can make your ECM work, but might have more trouble than if using something pre 01. Some sort of changes with how the ECM communicated with the guages or something?
- According to the Novak site - no changes in springs really needed - I would think there would be a need though. Time will tell. I have a Rancho lift and their springs were a bit stiffer than stock, so I might be Ok.
- I think (hope) you will be Ok with no AC - I dont have it either, yet my 4.0 ecm does - i believe you simply dont wire in anything on that circuit - no issue?
- You will need to relocate the weld on part of the motor mounts, using 4.0 mounts. Seems best bet is order them new.
- Your gearing with 4.10s will be great for some taller tires , with stock size tires, you will be spinning the 4.0 up a bit higher RPM. I think stock 4.0s have 3.57 or in some cases depending on tranny, even 3.07 gearing.
- I would bet that the 05 Rubi ECM has the SMART Key/SKIM stuff enabled. from what I understand, that crap started in 98 on some models but not all. Higher end models more than likely have it, and the newer it is, the more likely to have it. You have both...newer and higher end trim level. That alone might be a big road block. I got lucky - I am using a ECM from a 98 Grand Cherokee which did not have the SMART KEY stuff! Find out what the ignition key from the donor looked like. Grey end - SMART Key, Black end...not! Hope for black!
-Drive shaft length might be different. AX5 is shorter than a AX15. In my case I am using an AW4 - so definetly will deal with drive shaft issues.
- DO LOTS of google searches! Do LOTS of searches on any Jeep/Offroad forums you can find! Here is a link to some pics of an install in a TJ - I cant find the link to this guys post on Pirate4x4 - but he did a brief write up in a thread there. Good pics of the motor mounts location (though from what I read, best bet is to hang engine in place, pin down location that way - not trying to use measurement. http://www.jeepshots.com/shots/projects/4%20Liter%20Swap/
- Here is a link to a thread I started on the Michigan Wheelers forum - I will be updating it from time to time.
Best of luck! I look forward to reading some new threads on this!