Down hill and cruise control... - 2014+ Jeep Cherokee Forums
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post #1 of 22 (permalink) Old 02-08-2015, 04:20 PM Thread Starter
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Down hill and cruise control...

I am just wondering about the cruise control and how it functions. Previous vehicles I have owned with cruise enable and set, the vehicle tended to remain at the speed set going down hill. Yeah, it may accelerate a couple kms or so but the Jeep seems to increase and not slow down. Yesterday on a particular long down hill it accelerated to about 12 k/hr from where it was set to the point I had to hit the brake. Is this normal?
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post #2 of 22 (permalink) Old 02-08-2015, 04:36 PM
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Yes, very normal. At low rpm the engine is producing very little engine braking. Your speed is increasing because you are going down a hill..... If you want to maintain speed, move your shifter to the left and select 6 or 5, enough to get your engine rpm to 2500-3000 and you should have no problem maintaining the set speed. Also, learning to drive a manual transmission would probably help teach you a few things about engine speed vs vehicle speed. Something everybody with a license should know.
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post #3 of 22 (permalink) Old 02-08-2015, 04:40 PM
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Do you have regular cruise control or Adaptive Cruise Control with the ACC turn on? Regular will speed up (no braking) ACC will maintain going down hill.

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post #4 of 22 (permalink) Old 02-08-2015, 11:24 PM
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Quote:
Originally Posted by GCWIMMER View Post
Do you have regular cruise control or Adaptive Cruise Control with the ACC turn on? Regular will speed up (no braking) ACC will maintain going down hill.
However it does so by applying the brakes. I usually just hit cancel and move the stick left and bump it forward so it downshifts. Then towards the bottom of the hill (or whatever works) hit resume and bump stick back right so she finds the right gear and maintains the set speed.

I have not been using Cruise, just Adaptive Cruise, and the only fault I find is the use of the brakes rather than downshifting as the 45RLE in my 03 Liberty did.

YMMV

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post #5 of 22 (permalink) Old 02-09-2015, 05:11 PM
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Originally Posted by al7fi View Post
However it does so by applying the brakes. I usually just hit cancel and move the stick left and bump it forward so it downshifts. Then towards the bottom of the hill (or whatever works) hit resume and bump stick back right so she finds the right gear and maintains the set speed.

I have not been using Cruise, just Adaptive Cruise, and the only fault I find is the use of the brakes rather than downshifting as the 45RLE in my 03 Liberty did.

YMMV
When I was towing a 12' trailer across the country with ACC engaged, I found that it will downshift to maintain speed *sometimes*. Generally it will do brake application first, however. Once it has applied the brakes long enough, it will downshift if it can't maintain speed with light braking.

What I typically did was monitor what ACC was doing by watching the fuel economy gauge in the EVIC. When the gauge became maxed out at 99ish MPG, I knew the ACC system would begin applying the brakes downhill. From there, I'd just go to ERS mode and force a downshift of a couple gears (though typically I ran in ERS mode anyhow to limit top gear to 5 or 6 to prevent hunting). Then the ACC would achieve more braking through throttle control and would cease using the brakes.
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post #6 of 22 (permalink) Old 02-09-2015, 08:39 PM
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I just let it slow down using the brakes. I'm fine with that. Brakes are cheaper and easier to replace than transmissions.

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post #7 of 22 (permalink) Old 02-09-2015, 08:54 PM
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After only one experience with fading my brakes going downhill too enthusiastically back in highschool, I would not use my brakes to regulate my speed when going downhill, especially during long descents.

Brakes do overheat, and then they don't work.

Engine braking is the correct way to control descent speed. The brakes should be used to augment engine braking, but not to replace it. Especially on heavy cars like the cherokee.
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post #8 of 22 (permalink) Old 02-09-2015, 09:01 PM
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When I use ACC and I'm going down a hill I hit cancel and let the Jeep coast and actually speed up, I'd rather that than let the cruise apply the brakes, why not use the momentum to save fuel and avoid wearing your brake pads, then at the bottom of the hill when the speed goes back down to my set speed, I hit resume. On my Ram I basically do the same thing, the only thing is the truck downshifts to reduce speed instead of braking, like al7fi said in the earlier post.
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post #9 of 22 (permalink) Old 02-09-2015, 10:20 PM
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Originally Posted by sport_4x4 View Post
After only one experience with fading my brakes going downhill too enthusiastically back in highschool, I would not use my brakes to regulate my speed when going downhill, especially during long descents.

Brakes do overheat, and then they don't work.

Engine braking is the correct way to control descent speed. The brakes should be used to augment engine braking, but not to replace it. Especially on heavy cars like the cherokee.
At 4101lbs for the Trailhawk, I do not consider it to be a "Heavy vehicle" My 5500 lb Silverado is a lot heavier. Engine Braking is probably the best way to control/moderate downhill speed, but most people are not used to driving a 9-speed trans where the top 4 gears are all overdrives. Most are used to 4-speeds and an overdrive. Maybe 3-speed with overdrive depending on model year. It will take time for drivers to adjust. My 2012 Volt is set to use coasting to help re-generate the battery, so it will pick up speed on almost any downgrade. Took some time to get used to the idea of no engine braking. Adaptive Cruise Control may be different, I have no idea.

Last edited by SacsTC; 02-09-2015 at 10:27 PM.
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post #10 of 22 (permalink) Old 02-09-2015, 10:27 PM
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<<When I use ACC and I'm going down a hill I hit cancel and let the Jeep coast and actually speed up...>>

In my neck of the woods the next step would be noticing the flashing lights in your rear view mirror.

<<I would not use my brakes to regulate my speed when going downhill, especially during long descents. >>

That's where we only partially agree. On long descents, absolutely downshift and use engine braking. On rolling hills the brakes do the job, especially nice sized 4-wheel discs like the V6 Cherokee has. On top of that, the 3.2 doesn't seem to exhibit strong engine braking from my experience.

With a transmission as problematic as the Cherokee's seems to be, I think I'll avoid unnecessary downshifting. But that's just me.

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Last edited by Dodgeboy; 02-09-2015 at 10:32 PM.
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