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2021 JLUR won't coast downhill in 4Lo

flanders

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Love my Jeep. My most prized possession... until I'm driving downhill.

I drive up a steep canyon road in awe of my jeep's capability, loving life. Same road coming down I want to kick it in it's transmission.

4Lo won't hold me back! My dad (21 Bronco) and brother (21 Willys S) are coasting smoothly asking me why I'm on my brakes so much.

Thought it was normal til I found these two threads.

https://www.jlwranglerforums.com/forum/threads/2018-jlu-sudden-acceleration-downhill-in-4l.37338/

https://www.jlwranglerforums.com/forum/threads/19-jl-sudden-accel-downhill-in-4l.27161/

Both threads end without really identifying if this is normal behavior??

To be concise, in 4Lo going downhill:
1. Engine suddenly loses all 'hold back' and rpms surge. In manual mode too.
2. If I don't brake when it surges, it'll go up to 4000ish before some mysterious force pulls the rpms back down to normal. Then it'll surge again. Infuriating oscillations forever.
3. If I touch the gas at all, it sends it into this surge mode. Almost seems like I need to come to a full stop to reset it. Then it'll be good for a minute until it's to steep or I touch the gas. Then the rpms are at 4k again.

My question, is this normal? My brothers Jeep doesn't do this, but I have a lower low. If it is, great. If not, I'm going to be mad I just wasted the last year hating the thing every downhill.

Thanks in advance.
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Jim1964

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It might be helpful to mention what engine you have. I donā€™t experience this with mine.

I HAVE experienced what you describe with a number of different late model vehicles, not just FCA. I suspect itā€™s caused by making emissions a priority over your safety, and itā€™s throttling up to heat the catalyst or some such nonsense.

Correction: after changing locations to higher elevations-8-10k feet- it DOES do this. Not all the time. However frequently when coasting down the idle speed raises to 2200 rpm. So when conditions are right it will bounce between 2200 and 2500 just like it was on cruise control or something.

Shifting into N results in the engine continuing a high idle condition at 2200 for several seconds before it gradually slows down and returns to normal idle speed.

Thanks a lot, FCA! :no:
 
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bjm00se

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You're gearing down right? Not leaving it in "D" ? If so, what gear are you dropping it down to? Just checking the obvious.
 

Retrograde

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My question, is this normal?
No, it is NOT normal... mine does it too. And as time goes on, it becomes worse, and you notice it in High range, also (both 2x and 4x modes), in both 'D' and 'M'. (2020 JL, 3.6, AT. no Etorque)

Earlier this spring I was creeping down a teep, ice & snow covered Forest Service road and it decided to pull this crap, bolting down the hill. I had to jump on the brakes, and because the engine was fighting me, the anti-lock breaks didn't work, and the whole mess spun me around on the road and put me in the ditch.

My Jeep is about to go into the dealer for it, but I am not optimistic; anything more involved than putting air in the tires confounds my local dealer morons. So I'm also compiling information and other instances of this for a possible NHTSA complaint. Vehicles that accelerate by themselves and cause accidents is a pretty serious matter. (Watching this and other threads.)

Question for you, though: did you get notice of an emissions system recall? I'm wondering if the two are related...
 

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flanders

flanders

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@Jim1964
I've got the 3.6 with eTorque.

@bjm00se
It doesn't seem to care in D or M. Usually I go to M pretty quick because it's running away from me. I usually try to keep it in 2-3, maybe 1 for really hairy stuff. Does it in 4 as well.

@Retrograde
So is this on @JeepCares radar?
 

jessedacri

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@Jim1964
I've got the 3.6 with eTorque.

@bjm00se
It doesn't seem to care in D or M. Usually I go to M pretty quick because it's running away from me. I usually try to keep it in 2-3, maybe 1 for really hairy stuff. Does it in 4 as well.

@Retrograde
So is this on @JeepCares radar?
I'd consider what you describe to be typical of what my 2019 3.6 non-etorque auto does sometimes. I always thought it was odd but ultimately normal, tho mine is never so dramatic that I feel like I'm fighting active throttle application with the brake pedal. It for sure does "give up" on the engine braking and starts accelerating down hills in 4L on occasion.
 

BuyHold

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Can't you just put it in first or second gear, depending on how fast you want to go, and take your foot off the clutch? That always works for me.
 

Rico1111

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It seems that all are automatic transmissions.
 

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flanders

flanders

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So not normal... but normal? It bugs the heck out of me, but I know I'll drop it off at the dealership and two days later they'll say they drove it around and didn't notice anything abnormal. I was kind of hoping it just means some bad sensor (from factory?) that I could pay to replace. Doesn't look that way I guess.
 

jessedacri

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So not normal... but normal? It bugs the heck out of me, but I know I'll drop it off at the dealership and two days later they'll say they drove it around and didn't notice anything abnormal. I was kind of hoping it just means some bad sensor (from factory?) that I could pay to replace. Doesn't look that way I guess.

All of the JLs I've driven including mine, and those that I've been on runs alongside, have something like this behavior. Engine braking stops after ~2500rpm and it seems to add a little throttle instead. If you're getting like "runaway vehicle" vibes from it and you feel like its very challenging to stop forward progress with the brakes or further downshifting then I'd say there's an issue.

If anything I know there's two companies (Livernois and Diablo Sport) now making aftermarket transmission tunes/profiles for the ZF850RE transmission that might improve this behavior, but you'd have to be willing to go this route and risk warranty coverage. The feedback I've heard is extremely positive.
 

FINN 2.0

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I have a 2021 JLUR 3.6 and love the way 4/lo holds me back on hills. However, most of the gravel hills I have to use to get to the main road are no more than 20%.
 

At Risk Ute

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Have you tried the off-road plus button? I punch it going down steep stuff in 4L. Gears hang longer so Iā€™m not surging or riding the brakes. YMMV.
 

Stompr

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So I have been searching the interweb for days about this issue.

I have a ā€˜21 3.6 with a manual and it does this very same thing. 4 low, 1st gear or 4th, no matter. Coasting downhill with no throttle input and every 30 seconds or so, it winds up to 2200 then abruptly back down again. I have to brake against the engine running away to keep a controlled decent of any kind, at times to the point of killing the engine from that high RPM point.

Iā€™ve read numerous threads about throttle hang and idling madly high when itā€™s cold getting up to temp. Mine does these things as well and I understand why it is done, however this problem is at operating temperature, canā€™t possibly be for emissions and happens when I truly need NO throttle input.

It is problematic enough that I may decide to sell it if I canā€™t find a solution. Itā€™s dangerous but quite simply it makes me not enjoy using it off road which is exactly its purpose in life.

Itā€™s a relief, but not, that Iā€™m not only one that has experienced this. I thought maybe I had a problem child.

Iā€™m optimistic someone may see this thread and have a solution.
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