Manual Transmission Engine Braking Issue (?)

[OHJeeper]

Ok, so I've had my 2022 JT Rubicon 6MT for just over 8 months and FINALLY got to take it on the trails today. I had a 2018 6MT JLU Rubicon, so for the most part the same transmission/engine combination.

Today when descending a couple of hills in 4LO 2nd gear I would be cruising just fine at 1000-ish RPM and holding a steady descent with no brake pedal input, then all of the sudden it would accelerate and RPM's would go to near 3000. If I feathered the brake, the RPM's would drop back to normal range and it would hold again with the engine. I never touched the skinny pedal or the clutch ... and I don't remember ever having this happen on my JL.

Anyone else had this experience?

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[NachoRuby]

Are you using off-road plus? Throttle controller?

 

[OHJeeper]

Off Road+ was on

I do not have any throttle mods (pedal commander, etc) if that's what you were asking

 

[NachoRuby]

Yes that's what I was asking. You should see what it does w/o offroad plus, just for comparison. Strange indeed. But I always use offroad plus, and haven't noticed that.

 

[OHJeeper]

Appreciate the response, Nacho! Next time I'll try without OR+ and see what happens.

 

[zuki_dan]

I have noticed this same issue with the auto engine braking offroad. I believe it has to do with the emissions and electronic throttle opening the blade slightly causing the increase in rpm's.

 

[OHJeeper]

I have noticed this same issue with the auto engine braking offroad. I believe it has to do with the emissions and electronic throttle opening the blade slightly causing the increase in rpm's.

Are you running with offroad+ engaged or without?

If this is intentional behavior for emissions, that's REALLY bad (and unsafe) for offroading...

 

[zuki_dan]

I have noticed it with offroad+ on and off. Maybe not as noticeable with the auto but still does it during engine braking offroad in low range. I just bring the RPM back down with brake application. It is annoying though! Another reason to not like electronic throttle bodies.

 

[OHJeeper]

I have noticed it with offroad+ on and off. Maybe not as noticeable with the auto but still does it during engine braking offroad in low range. I just bring the RPM back down with brake application. It is annoying though! Another reason to not like electronic throttle bodies.

Do you use hill descent control on your auto, or just "manually" adjust the transmission to the gear you want? Wondering if the same happens with HDC... Not that I have that on my MT, but curious.

 

[zuki_dan]

Do you use hill descent control on your auto, or just "manually" adjust the transmission to the gear you want? Wondering if the same happens with HDC... Not that I have that on my MT, but curious.

I don't use the hill descent control because of all the noise from the abs motor. I manually shift the auto to hold gear. I recently just put the paddle shifters from the 392. I love the paddle shifters for manually controlling the gears offroad.

I haven't noticed it with HDC but that system does use the abs brakes to control the speed also.

 

[OHJeeper]

I don't use the hill descent control because of all the noise from the abs motor. I manually shift the auto to hold gear. I recently just put the paddle shifters from the 392. I love the paddle shifters for manually controlling the gears offroad.

I haven't noticed it with HDC but that system does use the abs brakes to control the speed also.

Thanks for the reply!

That whole paddle-shifter thread -almost- makes me wish I had the auto! Looks fun.

Speaking of 392, there was one in my trail group over the weekend. We did some hill climbs and he waited for everyone to get out of the way at the top and just nailed it all the way up the hill. Sounded AWESOME. I can't afford a $90k Jeep... and I love my manual so I'm outta' luck!

 

[amoyer_01]

Is this a different item then the engine trying to rev match? I dont have a Rubicon but I have a manual and coming to a stop sometimes without pushing in the clutch the engine will pump up the RPMs slightly.

 

[OHJeeper]

Is this a different item then the engine trying to rev match? I dont have a Rubicon but I have a manual and coming to a stop sometimes without pushing in the clutch the engine will pump up the RPMs slightly.

Yes, this is a different issue but the tachometer "symptoms" are similar - revs up on its own with no pedal input from you.

In this case, it's when descending a steep hill in 4LO and trying not to use the brakes, the throttle decides to increase revs to 3000 and the JT accelerates down the hill unless you apply the brakes.

NOT ideal, especially in tricky/slippery/steep areas.

Other MT issues (like what you referenced):

1. Rev Hang - holds RPMs high between shifts even when you let off the pedal. Usually happens at WOT or when waiting to shift higher in the RPM band
2. Idle float - RPM's sit at 2000-3000 when cold until you give it some pedal/brake input, then calms back down.
3. General Clutch "softness"- somewhat subjective, but many don't like the clutch feel and the fact that it can slip/burn because it's "weak" compared to a Centerforce or other aftermarket brand.

 

[NachoRuby]

Other MT issues (like what you referenced):

1. Rev Hang - holds RPMs high between shifts even when you let off the pedal. Usually happens at WOT or when waiting to shift higher in the RPM band
2. Idle float - RPM's sit at 2000-3000 when cold until you give it some pedal/brake input, then calms back down.
3. General Clutch "softness"- somewhat subjective, but many don't like the clutch feel and the fact that it can slip/burn because it's "weak" compared to a Centerforce or other aftermarket brand.

Rev hang and idle float are for emissions, so they aren't going anywhere. It's the only way you can buy an MT nowadays (any brand). It's For NOx emissions. It's been around in some form since at least 2008 or so, and is now ubiquitous. Our 2016 JK does it too. So did my 15 and 17 Subies and '08 and '19 VW. Hondas do it too. Modern automatics have it too, but you would probably never notice it.

Rev hang only occurs if your foot is still on the gas while you shift, though (even momentarily, or very slightly). If you take your foot off the gas before it gets to neutral, no rev hang. But yeah, that's reality now, and the only way they (anyone) can make a stick shift and meet emissions requirements.

The article below is one that I always reference that explains the "why's".

https://www.autoweek.com/news/techn...revs-slowly-on-purpose-to-curb-nox-emissions/

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