I have a couple questions about my Jeep. First what is the button that says power trans? I know what I think it does but I've never heard of it and its not in any manual have seen. But the big mystery is there are three things that went out at the same time that I believe llead to the same problem. just not sure exactly what would cause all three things to stop working. the first thing I noticed was I switched from heater to defrost and nothing happened the vacuum that operates that lever is not functioning properly.
Secondly the cruise control quit working. Last but not least the brake power booster stopped working with the brake assist. If anybody has any ideas where I should start first I would be more than glad to hear them. Or is it possible thmter that operates the brakes is malfunctioning and getting fault signals therefor sending fault PSI to faults tires

 

Power Trans is pretty much "tow mode", use it when towing. Idk about your other problems. Best bet is to post in the OEM tech section.

 

Sounds like you have a a vacuum leak somewhere, all those things run off of vacuum provided from the manifold.

Start checking the lines. And make sure you have a vacuum reservoir ball, should be behind the front bumper on the passenger side.

The trans switch changes the way it shifts. Just keep it on power.

 

Agreed.

Power trans makes the trans shift a little earlier, your mpg should stay the same I've heard of people getting better mpg on power mode, I personally get the same mpg in power or comfort.

It definitely sounds like you have a vacuum leak both the defrost and cruise control run off vacuum provided by the ball mentioned above, it's very common for those lines to break. Brakes work off the vacuum from the intake manifold as well so start poking you head around and listening for a hissing sound while the engine is on.

 

Thx for the info...it made me think and I remember hitting ice and sliding into. A mountab hitting the front passenger side. Maybe that ball got damaged. Should I take off grill or look through grill or is it in the engine compartment? Only had jeep a couple years but learned a lot about it. Thx again all for the insight. I will let ya know what I find. I also was driving last week and notice a burnt brake tpe smell and when I pulled over to check the frond pass.. well was smoking a liub was warm. I heard the calipers can sieze up? No grinding and wheel was stiff when I jacked it up so don't think it was bering? If caliper siezed do I have to replace or just free it up? I took off wheel n hub ang jammed greese in. Seems to be good but this is my first jeep n I'm still learning. Any help will be greatly appreciated.

 

That vacuum ball is in the bumper if you take off the passenger side end cap you will see it, it's tucked right up against it. You might be able to see it from under the jeep

 

You may have the Bendix 9 ABS on your 91 XJ. There is a recall for life on that system that should take care of the lack of assist, it's the 703 recall.