is there any differance between a 4.0 and 4.0HO, curious what years and models have the high output? any comments would be great

 

Yes, different fuel injection system and a redesigned head, at least. The HO has a bit more power (18HP) and a bit more torque. HO was '91 to '99 (I think they stopped putting HO badges on in '96), after that it was the "Power Tech" with a different intake manifold.

 

I'm reasonably sure my 98 has the H/O motor.

When I'm cruising along at about 25-30 mph & stomp the loud pedal to the floor, my XJ jumps into hyper-drive.

Several people have agreed that it feels more like a V8 than an IL6.

And a strong V8 at that, feels like an old double pumper carb with the primaries & secondaries wide open.

 

4.0 HO started in '91.

 

....96 was the last year, before 97 redesign, that it was badged H.O....97-01 the injection system, intake/exhaust manifolds were redesigned along with some other tuning/boring, but the i6 is relatively the same engine....even on the wranglers and grand cherokees through 07...

 

x2

 

The 4.0 had a helluva run, didn't it? Pretty much the same engine with just minor changes from 1987 until they discontinued it in '06/07. That's 19-20 years, in relatively unchanged form except for intake manifolds and fuel injection systems (ok, true, the block was reinforced in '96 and the head was recast in '00, but parts throughout this time period are interchangeable)! Heck, you could even lump it with the 4.2 (which the 4.0 evolved from and shares a lot with) and go all the way back to '71.