Hello all, I am thinking about swapping out my 91 ranger engine for one a bit newer. The current one runs just fine, but I would like to have an engine that produces a bit more power and one that has better fuel efficiency. My question is what other ranger engine years are compatible with my vehicle and could swap into my engine bay. Thank you!

I have a 4x2 4.0 L V6.

 

If you mean what engine with more power will bolt to your transmission, there is only 1.
You have a 4.0l OHV engine with 160HP, the newer 4.0l SOHC engine has 207 HP

These have a similar block/bell housing bolt pattern, SOHC has one extra hole I think.

You still need to swap Computer and engine wiring harness.
AND 4.0l SOHC only came with PATS computers and OBD II, so you will need to add a "wand" on your ignition key slot and an O2 sensor behind the Cat converter.
Your '91 should have a VSS(vehicle speed sensor) on the trans, but have a look, you will see where speedo cable comes out and there should be a wire connector on the same place, computer needs that.

Hopefully you have a manual trans, if not then that may be another can of worms.

I have read a couple of people suggesting the 4.0l OHV computer could run a 4.0l SOHC, I am sure it could "run it" since it is a MAF system but I doubt you would be happy with results.

All in all, you would probably be better of just doing the more common explorer V8 swap, engine and tranny.
A little more work, but more power and lots of how-to's for that