Vacuum problem?
 

1998 XJ Sport
220k miles
4.0L I6
4WD
4dr

​​To start with, I haven't driven this vehicle myself since the end of October. I was in boot camp, and now I'm in tech school. I'm going to be able to start driving/working on it next weekend. The issues that arose were observed by my dad during the 19 hour drive to get the vehicle to me.

My dad stated that during the second day of the trip, the Jeep would start randomly downshifting out of overdrive (68mph), he slowed down to 55ish and it dropped into 2nd. And he said that it would shift really weird. The next day when he started again, it wasn't doing it until later on.

I don't have access to my Haynes manual for a little longer, so I'm trying to get some advice on where to start. I've been advised that it could be a vacuum leak, but I can't find references to XJ transmissions being vacuum actuated after '91, maybe my GoogleFu skills are weak, I don't know. My dad also said that cruise stopped working.

I was having some occasional minor issues with it before I left. Twice it just didn't seem to want to shift, and it felt like the power from the engine just wasn't making it to the wheels. And it just seemed to be not very responsive when I would give it gas. The first time it lasted for a week, then I heard s mechanical pop and the problem completely went away. A week later it came and left (didn't hear a pop) within about two days.

In between the initial problem and the long drive, my parents and in-laws had it taken to a shop and had the transmission and front and rear differential serviced, new tires, new rear brakes, and a new exhaust+cat put on. Everything but the tires I wanted to do myself, but I wasn't able to get to it, and they were paying for it and didn't want to take the drive without the stuff getting done, so I wasn't complaining.

Some other issues that have been ongoing are that the AC doesn't work at all, and the heat only blows on max.

Does this sound like a vacuum issue to you experts? I'm thinking because if the age of the vehicle I'm probably going to go through and replace the vacuum lines throughout the system.

Any advice or thoughts?

Thank you for your service.

I had a problem with my 1998 that was caused by a blown AC clutch fuse. I don't remember the number of the fuse, but it was tied to the transmission as well. It was located in the panel at the passenger's feet. Check ALL of your fuses. Do not rely on simply looking at the fuses...use a multimeter. Good luck.

And now I can't replicate the problem... It's running perfectly fine, except for the issues that I already had.

Note from DJ
Here is some information that I had saved about a 99 cruise control not working.
It’s worth a quick look.

OP by outracing with a 99
The issue that I am having is that I have just installed an advanced adapters SYE kit on my XJ. Since the install, I no longer have cruise control. My speedometer works, and the light comes on, but even if I am at 50mph, my cruise control won't set. Is there a fuse or perhaps a line that I should check out? Thanks for any help!
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Post # 2 by Op outracing
So okay, no one seems to know. So here is the deal. I'll post my findings in case someone else needs the info.

While working on getting the SYE kit in, I had the hood open. When I was all finished, I closed the hood, but when I did so, I dropped the prop rod. When it fell, it fell in such a way that it severed a vacuum line right there by the cruse controller. I replaced the line with a small section of hose, and now the cruise works.

Your heat only blowing on max is a classic sign of a bad blower motor resistor. The speeds below "Max" are limited by the resistor. If you have melted wires around the resistor you probably have a bad blower motor as well (it's drawing too much power causing the lines to melt.)
It's an easy fix with plenty of good write-ups and videos.

Thank you for your service. :)