This is the problem that I'm having with a newly acquired 2000 Cherokee XJ. It's lifted and also seems to have some gear issues bc it struggles to hit anything north of 65mph if on any sort of incline. I wonder if this is due to the lift and large, heavy tires. But the main concern (unsure if related to the speed/power issue or not) is that I've had it not start on me twice now in a one week period: once after driving about 60-90 minutes on the freeway on a slight incline the whole way. Was in a parking lot for about 10 min and then wouldn't start. Waited about another 10 min and then started without issue. Started again a couple times that day, both times after sitting for awhile. The second time it happened after driving 30-40 min on a multi-lane road going maybe 45 mph tops or so. Went in to a grocery store for 20-30 min and wouldn't start. Finally did after some patience. Then about 45 min later I felt all power to the engine seemingly die while going up a mountain road. Tried it periodically over 60-90 min period, but no success. Had to get towed a couple of miles to our destination. Then it started 36 hours later with no issue.
Note it doesn't at all seem to be the battery. Lights, radio, etc. seem to go fine. The battery is relatively new. There is no clicking sound when trying to start the car. You can tell it's trying, just doesn't turn over. The car seems to have no problem starting if it's stayed on surface roads for a mild period of time. It also seems to have no issue if starting after sitting overnight or anything.
If anyone has any insight, I would REALLY appreciate it. I'm not a car expert at all -- was living in a city for 10 years where I didn't have one. I tried taking it to a well-rated mechanic today, but they couldn't get it to not start, so said they couldn't diagnose the problem. Super frustrating. I'm worried I'll have to learn everything myself to take care of it, and am totally clueless where to begin.

 

a few issues and problems could be present

the speed issue could be, but shouldnt, be due to large tyres, what size are they ?

the non-start issue could be a few things

1) dirty NSS switch prevents engine starting...if it is an auto, rock the lever thru neutral and park with key in start

2) crank position sensor on its way out, gets old and fails, this is the main sensor that is needed to start the engine

3) bad earths or main cables ..you mentioned you felt a loss of power...it is essential to check these on an XJ..se extensive archive posts

4) bad starter motor, which can be easily removed and tested on a lifted vehicle

 

I would remove the starter, take to to an auto parts store and have them test it.
My jeep had the same exact start problems.
Was a bad starter..

 

Just to be clear.

Not starting means-- Engine NOT turning over when you turn the key? OR Engine not starting and running after you turn it over.

Seems the "starting " is confused some time as engine running vs. turning over.

A "help outline" of facts would be nice, people could use and get to the issue a little quicker do to the replies taking time.

A lot of extremely knowledgeable people here and I know its trying to them sometimes......

 

1. I'm assuming the starting issue is one where the starter is not turning the engine over, i.e., the starter motor isn't engaging. This condition exists until a cool down period and then the starter engages. This could be the starter solenoid contacts just barely making when hot from conducted engine heat causing thermal expansion and then re-making of the contacts when cooled down due to thermal contraction. That's a wild guess.

2. Running speed - get us numbers from your tachometer (RPMs) when you feel the engine shifting through each of the gears, and when it's at cruise speed. This is indicated by watching the RPM indicator needle rise while accelerating and then dropping down with each automatic gear change the transmission performs. Each dropping down event should occur at a certain RPM and basically indicates to the learned eye when proper changes are occurring. The average person does not acquire this level of awareness of the vehicles they operate, which is normal, but when problems arise it's good to become a little more in tune with what is/isn't normal for your vehicle. In your case, you're new to the XJ and it has a problem. There will be questions asked and advise given.

3. Does your XJ have a damage history report? You should be able to access one for your VIN number. https://vincheck.info/free-vehicle-history

4. Do you have any service history obtained from the previous owner?

5. When you shift from park to reverse, or drive, and let off the brake pedal does the vehicle begin to roll without pressing the accelerator pedal? If not, how much pedal pressure is needed to get it moving? We all get a feel for what normal is, which is similar in any vehicle, but you're experiencing a problem and nuanced details could indicate something amiss. This question relates to wheel drag.

6. After you finish your next drive and park the vehicle, go to each of your wheels and place your hand in close proximity to the center of each to see (feel) the radiant heat and if one wheel is giving off more than another. Relatedly, does the vehicle want to wander (pull) to the left or right when traveling. Most will fall off to the down-slope of the berm (crown) in the road but I'm not addressing that. I'm addressing any wheel drag that might be occurring.

In any case, keep the information coming. All is helpful. And, welcome to the forum and the XJ.