2016 Trailhawk Trans question: coasting? - 2014+ Jeep Cherokee Forums
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post #1 of 13 (permalink) Old 11-12-2016, 02:59 PM Thread Starter
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2016 Trailhawk Trans question: coasting?

I have 'felt' that when coasting downhill and I very lightly touch the brake, my jeep speeds up.
As though the engine breaking disengages.
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post #2 of 13 (permalink) Old 11-12-2016, 03:09 PM
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Originally Posted by Ol_mp View Post
I have 'felt' that when coasting downhill and I very lightly touch the brake, my jeep speeds up.
As though the engine breaking disengages.
My first post and glad to be here.
Ol Mp
Given it's a 9-speed transmission, there will be a number of characteristics that will be unique with this transmission.

Most likely, what you are experiencing is the rev match to enable the shift from 5th gear to 4th gear.

This 9-speed transmission has two dog clutches. Dog clutches are more of a manual transmission thing and not common in automatic transmissions. Many manual transmission have synchros that spin up the dog clutch gears so they can engage. The 9-speed does not have synchros (to save space) so the engine, under computer control, revs to spin up its end of the dog clutch so the gears can engage. If you've used a manual transmission before, it's very much like blipping the throttle while downshifting while letting the clutch out.

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Last edited by Array; 11-12-2016 at 03:12 PM.
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post #3 of 13 (permalink) Old 11-12-2016, 05:01 PM
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Welcome. Excellent information here.

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post #4 of 13 (permalink) Old 11-12-2016, 07:07 PM
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Yes I agree with Array. On previous autos whrn coasting down a hill if you tapped the brakes they would downshift to add additional engine braking.

These do the same by idea, but it doesnt work. Firstly to down change it has to rev up lime Array describes, then once it matches and shifts it doesnt let off the throttle much so the revs dont try to drop and give the engine braking effects. At least not straight away. If its a really long hill you evently notice a feeling like you finally took your foot off the accelerator. I think that is something to do extra emissions control

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post #5 of 13 (permalink) Old 11-12-2016, 07:28 PM
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.... I think that is something to do extra emissions control
Good point. Someone commented recently that when the KL coasts fuel economy goes to 100%; 99 mpg on my DID. They said the fuel injectors are turned off. But when engine braking is occurring the fuel economy goes down the can. I tried this the other day and found it to be true. Coasting downhill got me 99 mpg. Shifting over to ERS and forcing a downshift netted ~14 mpg. My question is why aren't the fuel injectors turned off during hard engine braking?

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post #6 of 13 (permalink) Old 11-13-2016, 02:10 AM
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I've had similar experiences when using the ERS (Electronic Range Selector) to downshift in order to use engine breaking going downhill towards intersections. It definitely feels like the Jeep is speeding up when it shifts down, but maybe it's only an illusion cause by increased revs. Engine braking is not very useful with this transmission, in my opinion.

My '14 shows 2 L/100km (117.6 mpg) when coasting.

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post #7 of 13 (permalink) Old 11-13-2016, 10:16 AM
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My '14 shows 2 L/100km (117.6 mpg) when coasting.
My 16 does the same thing when I coast.

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post #8 of 13 (permalink) Old 11-16-2016, 11:43 AM
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I've had similar experiences when using the ERS (Electronic Range Selector) to downshift in order to use engine breaking going downhill towards intersections. It definitely feels like the Jeep is speeding up when it shifts down, but maybe it's only an illusion cause by increased revs. Engine braking is not very useful with this transmission, in my opinion.

My '14 shows 2 L/100km (117.6 mpg) when coasting.

I agree with you, When I am in cruise control my TH will downshift and keep the speed about the same going up a hill, but with cruise on and going down hill it just speeds up until I have to brake some. Even in ERS I have to get it to the lowest ERS position to do anything and that is about too low.

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post #9 of 13 (permalink) Old 11-16-2016, 09:29 PM
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I agree with you, When I am in cruise control my TH will downshift and keep the speed about the same going up a hill, but with cruise on and going down hill it just speeds up until I have to brake some. Even in ERS I have to get it to the lowest ERS position to do anything and that is about too low.
Sounds like they have changed something. My 2015 when going downhill with cruise on and foot off the throttle, will try it's darndest to keep the speed the same. It shifts down and down and down on its own many times keeping the tach at 4,000-5,000 rpm but on long steep hills still can't keep it from speeding up a bit. If I get on the brake the downshifting stops like it's saying ok, you've got it now, I don't have to try to keep speed down anymore. With cruise off it doesn't do this downshifting either, but without cruise it isn't supposed to try and keep speed the same.
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post #10 of 13 (permalink) Old 11-16-2016, 09:40 PM
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Mine applies brakes automatically when going downhill whether on ACC or just normal Cruise. Might be part of the tech pack??

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