* Engine choice: "4-liter engine" is quite broad. Are you talking about a 4.0L AMC inline-6 (a common swap and relatively straightforward), a 4.0L inline-6 from a different manufacturer (like a Ford or GM), or a V6 or V8 of 4.0 liters? The complexity varies dramatically. The AMC 4.0L is the most popular and easiest option for a CJ swap.
* Transmission: The existing transmission likely won't work. You'll need a transmission compatible with your chosen 4-liter engine. This might mean a new transmission, bellhousing, clutch, driveshaft, and potentially transfer case modifications or replacement.
* Engine mounts: You'll need custom engine mounts to fit the new engine into the CJ's engine bay. These are usually not readily available and will need to be fabricated.
* Wiring harness: You'll need a wiring harness compatible with the new engine and potentially an aftermarket engine control unit (ECU).
* Exhaust system: The existing exhaust system will not fit. You'll need a custom exhaust system.
* Cooling system: The cooling system may need upgrading or modification to handle the new engine.
* Fuel system: You might need a new fuel pump, fuel lines, and potentially a different fuel tank or fuel tank sending unit.
* Computer/ECU: Depending on the engine and year, you might need to address the computer/ECU. For a later-model engine, you'll likely need to manage this effectively.
* Body modifications: You might need to modify the firewall, hood, or other body parts to accommodate the new engine.
* Inspection and registration: Depending on your location, you might need to have the swap inspected and registered.
In short, while it's *possible*, it's a major project requiring mechanical skills, fabrication skills, and potentially considerable expense. A 4.0L AMC inline-6 swap is the most commonly done and relatively easier option, while other 4-liter engines present a much greater challenge. Thorough research and planning are essential before undertaking this project. Consult Jeep forums and other resources for detailed information specific to your chosen engine.
