Some gen one two door 3.0 did not even come with one. So I would say it is not critical to have one. But if you want one you are going to have to tear into it and see what you can do.

99 Montero....15mpg! Sold (so sad)
02 Jetta TDI....48mpg!
03 2500 Ram QCLB Cummins....18mpg
02 2500 Yukon XL, We out grew the montero, at least it has one locker.....13mpg (sold)
01 montero limited