99 XJ to MJ engine transplant

Can anyone tell me how hard it would be to swap in a 99 4.0 into an 88 MJ?
I know the electronics are totaly diffrent. I can get the entire harness and ecm with the engine for a hell of a deal but I just need to know what I'll be in for .

TIA
Carmine B
Ocala FL

Physically, they are the same block and use the same mounts. What you're in for is completely rewiring the engine controls. Also, the fuel pressure is different for the newer engines, so you probably need an adjustable fuel pressure regulator ... although the stock regulator might handle it.

figure out a way to stuff the XJ's entire gastank under the MJ, you'll need to run all new fuel lines as well as do the wiring.

my suggestion would be to get the entire 99 XJ and swap just about every single piece you can. (you'll practically have to use the 99 dash unless you can clusterfawk the instrument cluster, heater contols, steering column, etc into the old style dash)

if your MJ's a 4-banger, you'll have to swap the frame horns that the motor mounts bolt to (they are different, 2.5 vs. 4.0)

Could be wrong- but my MJ's fuel tank looks like an XJ's tank turned sideways.

As said above, the engine will bolt into place with no problems. Beyond that, it's only wiring.

Easiest way is to score a FSM for both vehicles so you have the complete wiring diagrams and splice from there.

Really shouldn't be too hard if it's just the engine, you will need some older senders for the gauages to work. If it's the same trans the speedo will work.