Bishop

If this has been addressed or is a common issue I apologize, I did some searching and didn't find anything related, but I can't say that my searching skills are top notch.

So, I noticed this a few months back and I've kinda been keeping an eye on it and I think I have it "diagnosed" but I haven't the slightest clue where to start when it comes to troubleshooting what is causing the issue....

I can drive around all day every day in 2wd, no hassle, no problems. I put the Jeep in 4wd (specifically 4low, I haven't tested high) and drive it on the trail for a while, no big deal. But the problems arise after parking for a few and letting things cool down while enjoying the outdoors outside the Jeep. When I start the Jeep after it's been parked, after it's been driven around a little while in 4low, it stutters and runs like garbage, I would say it's misfiring as well... I apply some throttle and let it run to like 2.5k or 3k-ish for like 10 seconds and it seems to smooth out, run on all cylinders, etc... basically back to normal.... When it first started, it wasn't happening every re-start, but I've gone to the trails 3 times in the past month and it's been getting progressively worse, having this issue every time on all 3 trips, ONLY in 4wd... This past trip, last weekend it actually threw a code but I couldn't get to a reader in time. I'm sure it's saved but I haven't bothered..... I haven't bothered because when I'm back at the trail head, I pop the Jeep in 2wd and it starts up, idles and runs like normal, and away I go....

So............. WTF? haha..... Anyone heard of this before? Again I'll say I did some searching and even the most basic keyword searches turned up nothing.

Monster Mopar

Not really sure. The only thing related to the engine and 4wd is some vacume lines if you have a disconnect axle. But if it were a vacume leak I'd think it would do it instantly when you engage 4wd. I wonder if it's more about the style of driving that is done when in 2wd vs 4wd.

Nevertheless the first thing you should do is go pull the code.

Bishop

I'm a more mellow driver off-road than I am on-road, and I'm a mellow on-road driver haha... I made peace with the fact long ago that my Jeep wasn't going to be winning any speed contests, so I just mosey around town. If I have some time tomorrow I'll try to pull the code.

89Laredo

Sounds like heatsoak to Me, they get warm crawling around in 4low.
Especially being a 2000.

freegdr

id def check and see if there vacuum line issues at the tc rea.

freegdr

x2 changing to 2wd is stopping avacuum leak whish will change mixture

Monster Mopar

Maybe you are having a case of vapor lock, the engine generally will run hotter in 2 low, when you shut it off the fuel in the rail boils off and then runs like crap for the first couple of seconds after restart, once the fuel pump catches back up it runs fine.

A simple test would be next time you're out offroading and turn it off. Before restarting cycle the key a few times (maybe 5??) to allow the fuel pump to reprime the system. Make sure you let the pump run the entire prime cycle before truning the key off and then back on.

89Laredo

It's a 2000, nothing vacuum related to do wIth 4Wd..
Reread the OP, it runs like crap on restart. Classic heatsoak on 99+.

Monster Mopar

A vacume leak you cause the problem the instant he engaged 4wd, not just after driving it in 4wd for a while then turning it off, then restarting

freegdr

it would cause a higher idle but add heat soak to the equation which affects what 2 cyls i think and its gonna add to the heat soak issue...

Bishop

What's the heat soak issue? I'll definitely pull codes tomorrow.... Heat seems like it would persist even in 2wd... I can stop at the end of the trail, kill it and put it in 2wd, reattach discos, and start it without issue... Seems like if the heats going to do something to 4wd, why not do it to the 2wd 10 seconds after its switched?

89Laredo

Seriously. Do I really have to say this three times?
There is NOTHING, I repeat: ABSOLUTELY NOTHING vacuum related to do with the 4wd system on a 91+. This jeep is a 2000, it DOES NOT have vacuum disconnect, It DOES NOT have vacuum lines going to the transfer case.
Its not a Renix Freegdr, no matter how bad you want to push your renix "knowledge" into this.
It runs like crap on restart after being ran at high rpm and heating up, classic heatsoak which is a known problem on 99+ jeeps.

2000 FSM Tcase removal Diagram. See any vacuum lines? Nope!

Bishop

What do you consider high RPMs? Or at least high enough in this situation

Monster Mopar

I think it's more about the length of time it's been shut off, just not that it's been shut off. After a engine has been turned off temperature continues to increase for a period of time prior to decreasing. The time you shut down and rest on the trail must be longer than compared to the 10 seconds at the end of the trail. The time you spend at the end of the trail clearly isn't enough time for the effects of heat soak to set in, which can include vapor lock like I mentioned earlier.

The reason this doesn't happen in 2wd is because opperating temperatures are higher when running in 4wd especially low range.

Bishop

I know heat is still present but it did this once or twice during winter too if that might matter. Snow bashing still had some stumbling issues