IIRC, the change to HO was 1991 for the XJ Cherokee. However, it wasn't
just a computer change: Jeep also redesigned the head, intake manifold and
exhaust manifold.

It's not impossible to upgrade to HO, but it's a bit of work. check out
rec.autos.makers.jeep+willys for a lot of people that know a lot more about
it than I do

Chuck


"James Morrow" > wrote in message
om...
> hey everyone! got a question for all you jeep gurus out there... i'm
> sure that someone can answer my question for me. ok, i have an 88
> cherokee with the 4.0 in it. now i remember a while back when i was
> just searching around reading articles on the internet someone said
> that the only difference between the regular 4.0 and the high output
> was the computer? the old was made by bendix if i remember right?
> anyways, in the same post i read that when they switched over to the
> high output jeep offered a mopar upgrade kit to turn the old 4.0 into
> the HO. i went to my local jeep dealership's parts dept to talk to
> them, and they said that they haven't heard of it and if it does exist
> then it was probably made by an aftermarket manufacturer. however, he
> didn't seem like the smartest guy in the world and he didn't even
> bother to look for it so there might be a mopar upgrade. my question
> is have any of you ever heard of this kit? if it is a mopar part do
> you know the product number? if it's aftermarket who makes it? i
> really want to do this. have any of you ever done this before or heard
> of it being done? money isn't too much of a worry so im not too
> concerned with the cost. a friend suggested that i go to a junkyard
> and pull the computer and all the associated wiring of a newer
> cherokee, but i don't know if it's just that simple. any input would
> be greatly appreciated. thanks in advance!
>
> james morrow