Hi all, I'll start with a little back story. Long ago I overheated the XJ badly (to the point of shutdown) when a freeze plug sprung a leak. Fixed the freeze plug and thought all was well. Months later it started to develop another overheat issue, and this time I started to notice exhaust leaking into the coolant. Replaced head gasket and there was no improvement. Convinced I needed a new cylinder head, I parked the Jeep and it sat for over three years.

Fast forward, and I have replaced the cylinder head and the entire cooling system and a host of other parts. Plenty of short trips near the house, and all seemed great. I took it out for a shake down run and discovered this new problem. The Jeep seemed to run just fine including plenty of rocky climbs in 2wd and 4wd full time. However, when in 4wd low, and crawling through a steep rocky section the Jeep would sputter then die. When I backed off, it would start right back up with no issue. It doesn't seem to be related to being at a high angle, but more an issue of when the engine is under a heavier load. My first thought is fuel filter and/or pump, or maybe a vacuum issue, but before I start throwing money and time at parts I thought I would reach out to see if anyone had any ideas to help diagnose it.

Thanks in advance,
Matt

WELCOME to CF.

CEL (check engine light) or any codes?

Thank you, and no CEL and no codes.

does it overheat, either by gauge, or monitor temp via plug-in OBD2, when stalling in 4wd Lo ?

fuel filter is also a cheap item worth changing,

on some models, there is a in-tank filter sock for the fuel pump...they can get very dirty

I didn't have my scan tool, but the temp would get up to around 220 on the gauge. All in we did about 120 miles starting at about 105 degrees outside and cooling to about 85 in the mountains. The Jeep temps stayed in control and never got above 220ish and that was early on when it was hot outside and climbing.

I will probably go ahead and pick up a filter and probably a pump too. I haven't been able to recreate the issue here in town, so even when I replace some parts, I won't know if it fixes the problem until I can get it back out on a trail.

CPS? Mine did the same thing late last fall while on a day trip (so it was very cool out) and didn't throw any codes. Stalled maybe four or five times regardless of incline or load, and only while in 4Lo. It had a little trouble firing up maybe two or three times. If the CPS is the original from the factory, it might not be a bad idea to replace it (only Mopar) or at least give it a good cleaning.

I did replace the CPS many years ago, though probably not a Mopar unit. I would have thought that a CPS problem would happen under any circumstance rather than only under specific conditions. Also, I haven't had any issues with starting, which I would expect if it were a CPS. Hmmm?

try a long steep hill, take off from still, maintain WOT long as you can...if its the fuel pump or filter, you would expect to feel an issue within ~30secs