Topic: What would it take...

[1lonejeeper]

To take to put a 2.5 out of a 99 tj into a 90 yj with a 2.5 And wound it be worth it.  I have a chance to get it for dirt cheap, motor, wiring harness and computer.

[jagular7]

If you need a replacement, then the labor to install the engine and hook up the electrical may be too much unless you do it yourself. Think about just using the long block as a replacement to your current engine. That might be a better scenario for you.

[st.chevrolet]

As with any engine swap your big question is; what are you hoping to gain by going to your new engine choice ?
To me going from a stock 2.5L for a newer stock 2.5L would not be worth your time, unless your doing it just to have a bit different from your everyday engine swap for the sake of doing it. There wont be much of a gain in horsepower & torque, so is it worth the the time and the money to put in the newer 2.5L in my opinion no.
But it all depends what your plans are for your Jeep.

[Jeffy]

What would it be like?  Well it would be like having 10 more hp and a slightly better gas mileage.  It would be a lot of work though.  You would want to have access to a complete salvage and park the two next to each other and start transferring parts.  There are a lot of differences but luckily, it's all bolt-on.

Problem with the TJ is that they changed a lot of stuff that might not bolt-on to your YJ.  Frame mounts will need to be changed as well as the engine mounts.  The gas tank will need to be figured out unless you just go with a fuel cell.  Gauges will need to be changed or go with aftermarket. Emissions will need to be transfered over as well.  Fuel lines, etc.  You'll have to figure out how to run the axle disconnect for disable it and run one-piece shafts.  It would be a lot easier to go with a YJ MPFI then a TJ as everything would be bolt-on.

I don't think it's worth it to convert everything to work with the TJ though.  With that amount of work, you could install any number of engines.  A 4.0L comes to mind on the easy scale.  Same amount of work but with a better engine.  Otherwise a Chevy V6 or SBC would probably be easier since they make harnesses for those already.  3400 or a 3600(SC) would bolt up to the transmission if you wanted to go that route as well.

If all you want is a fresh motor then you could take the engine and swap your manifolds onto it and keep everything stock otherwise.