Major Challenges & Considerations:
* Engine Mounts: The engine mounts are different between the YJ and TJ. You'll need to fabricate new mounts or adapt existing ones, likely requiring welding and significant fabrication skills.
* Transmission: The transmission may or may not be compatible. While both used AX-5 or AX-15 transmissions, there might be subtle differences requiring adaptation or a complete transmission swap. The bellhousing bolt pattern might differ, requiring a new bellhousing or adapter.
* Wiring Harness: The wiring harnesses are completely different. You'll need to either completely rewire the TJ harness to accommodate the YJ engine, or rewire the YJ harness to work with the TJ's electrical system. This is a very complicated aspect of the swap.
* Computer/ECU: The YJ's computer is incompatible with the TJ's system. You'll need to source a compatible ECU, likely from a similar-year YJ, and ensure it's properly programmed or potentially use a standalone engine management system (a significantly more advanced undertaking).
* Exhaust System: The exhaust system will not fit. You'll need a custom exhaust system fabricated.
* Fuel System: The fuel injection systems and lines are likely incompatible. You might need to adapt or replace fuel lines, injectors, and possibly the fuel pump.
* Radiator & Cooling System: The radiator and associated hoses may not be compatible, requiring replacements or adaptation.
* Driveshafts: The driveshafts might need to be modified or replaced due to differences in engine position and/or transmission.
* Body Modifications: You may need to modify the engine compartment or firewall to accommodate the YJ engine, particularly considering potential differences in size and accessory placement.
What You'll Need:
* Mechanical Skills: This isn't a beginner project. You'll need extensive mechanical knowledge and experience with engine swaps and fabrication.
* Welding Skills: Fabrication of engine mounts and potentially other parts will likely be necessary.
* Electrical Knowledge: Dealing with the wiring harness is arguably the most complex aspect of the swap.
* Tools: A comprehensive set of tools including wrenches, sockets, a welder, a cutting torch, and potentially specialized tools for working on the engine and transmission.
* Parts: Beyond the engine itself, you'll need a wide range of parts, including mounts, possibly a transmission, wiring harnesses, an ECU, exhaust components, and potentially various other components.
* Time: Expect this project to take many weeks, even months, depending on your experience and access to resources.
In short: While technically *possible*, swapping a 1992 YJ 2.5L into a 1998 TJ is a highly complex project best left to experienced mechanics with significant fabrication and electrical skills. The time and cost involved likely outweigh the benefits unless you have specific reasons for needing to use a YJ engine (and have the expertise to perform the swap). Consider the feasibility and expense carefully before starting. A more straightforward upgrade would involve sourcing a compatible used engine and transmission for the TJ.
