I have a 90 YJ the only thing i dont like is that its carbureted and am thinking about looking for an aftermarket or even stock 4.0 to swap something fuel injected I was just wondering if anyone has done this before and how complicated it is and also is there any websites where you can see these motors and prices,

Yep! It's been done.. Prolly a lot less trouble and maybe cheaper to simply sell that one and buy a 91 or newer that already has the 4'0 in it.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

im assuming since its carb'd its a 4.2, find a later yj or cheeroke with a 4.0 and a computer and swap it into your yj, im sure if you search google you will be able to find info on it

if you have the 4.2 and it's carbed, you can swap just the head, computer and all of the fuel injection stuff off of a 4.0. Quite common.

you can just take it off of a stock 4.0 or is it some aftermarket part that you would have to order, because the jeep has around 130k so i wasnt sure if it would be worth it to buy these upgrades or just buy a whole new motor?

Kingdude Swapping just the head and injection is harder than swapping the complete engine and fuelie.. And prolly not cheaper either. Sometimes the head holes and the head bolts are different sizes. Most times the head shop has to weld up several coolant passages in the head.. You will end up with a larger size engine but one must work for those inches.
Changing the system over to fuelie will entail using the complete system off of the donor vehicle. In your garage it will most likely take weeks to get her going. Specially if you havn't done the deed before.
In the long run you prolly will get off cheaper if you sell the Jeep and purchase one with stock fuel injection.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

CJoffroad.com has a forum full of info on this subject. I would suggest buying a wrecked xj and using what you need. I used the AW4 4 speed automatic in my swap. For the rocks the automatic is great. You will want to study up on how to wire it but its not that bad.