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-   -   when coasting very sluggish not smooth deacceleration (http://www.jeepgarage.org/f107/when-coasting-very-sluggish-not-smooth-deacceleration-51220.html)

morty346 12-06-2012 10:09 AM

when coasting very sluggish not smooth deacceleration
 
I am sure someone has posted on the forums, but my keywords dont seem to come up a match

If I accelerate to around ~25-30mph and then let go of the pedal I would expect a smooth deceleration instead I get something describe as a "fish on a line" or very jerky slowdown, seems like it will kill my gas mileage because I do a lot of city driving and would be nice to coast between red lights... but it slows me down enough that i have to use the gas to keep a constant speed

(11 GC overland v6 2WD)

HammFist 12-06-2012 06:39 PM

Re: when coasting very sluggish not smooth deacceleration
 
The transmission automatically downshifts when you take your foot off the gas for long enough (the engineers have assumed that you want to slow down). The downshift is what you feeling.

morty346 12-07-2012 08:23 AM

Re: when coasting very sluggish not smooth deacceleration
 
Quote:

Originally Posted by HammFist (Post 720860)
The transmission automatically downshifts when you take your foot off the gas for long enough (the engineers have assumed that you want to slow down). The downshift is what you feeling.

Isnt the engine suppose to "learn" my driving habits, and NOT do this?

if I accelerate higher and it will coast forever(or so it seems) its just when I only get up to 20-30mph that it does this

Jeep_addicted 12-07-2012 09:47 AM

Re: when coasting very sluggish not smooth deacceleration
 
Morty

Here are the usually shift points.

1st to 2nd = Usually 15 MPH Under light throttle
2nd to 3rd = usally 26-27 Mph under light throttle

If you are mashing the pedal aggressively it will hold the gear longer so the shift point will will be higher.

After you get up to third gear you are usally cruising in the 30-35 mph range and it will take a while longer to downshift once at speed.


The tranny shift logic takes a while to learn you and you to learn it.

I will give you an example if you are in stop an go traffic not exceeding I think e 9-10 mph it will hold 1 first.

So you may think that is had shifted to second when it was still in 1st so that when you back off the pedal you get that jerky lift off.

The TCU will learn your style but it take about 1000 miles. If someone else also drives the same vehicle regularly it takes longer before it smooths out its adaptation.

bill_de 12-07-2012 10:08 AM

Re: when coasting very sluggish not smooth deacceleration
 
I've read on various forums dedicated to different brands about vehicles learning driving habits.

So far I have been unable to find any documentation from a manufacturer addressing this.

Maybe I don't know what terms to search. Can someone give me a link to any manufacturer's site where they explain this feature?

Thanks

2012 Summit 12-07-2012 10:50 AM

Re: when coasting very sluggish not smooth deacceleration
 
Quote:

Originally Posted by bill_de (Post 721107)
I've read on various forums dedicated to different brands about vehicles learning driving habits.

So far I have been unable to find any documentation from a manufacturer addressing this.

Maybe I don't know what terms to search. Can someone give me a link to any manufacturer's site where they explain this feature?

Thanks

Try this:

Let me google that for you :)

bill_de 12-07-2012 11:20 AM

Re: when coasting very sluggish not smooth deacceleration
 
Adaptive ... why didn't I think of that?

I really appreciate the Google search. :thumbsup:

yoda42 12-07-2012 06:59 PM

Also if you take your foot off the accelerator suddenly the GC thinks you are possibly trying to avoid a crash, so it starts to apply the brakes before you do to shorten the braking distance. Try easing your foot of the accelerator

HammFist 12-07-2012 07:04 PM

Re: when coasting very sluggish not smooth deacceleration
 
Quote:

Originally Posted by morty346 (Post 721060)
Isnt the engine suppose to "learn" my driving habits, and NOT do this?

Nope. There is no way for the Jeep's ECU to know that you do not in fact want to slow down when you take your foot off the gas for several seconds (since the rest of us do). The only way you can "fix" this is to reprogram the ECU so it never downshifts while coasting, and as far as I know, we can't do that yet.

2012 Summit 12-08-2012 07:05 AM

Re: when coasting very sluggish not smooth deacceleration
 
Quote:

Originally Posted by bill_de (Post 721144)
Adaptive ... why didn't I think of that?

I really appreciate the Google search. :thumbsup:

You're welcome.

JoeSchmoe007 12-08-2012 10:47 PM

Re: when coasting very sluggish not smooth deacceleration
 
There was a TSB (software flash) for earlier '11 WK2 with V6 to improve driveability. It is listed there:

Jeep Grand Cherokee WK2 - Grand Cherokee Service Bulletins and Recalls

but I just can't recall exactly which one this is. I had it done and it made noticeable difference. If you didn't have it done you should.

JoeSchmoe007 12-08-2012 10:50 PM

Re: when coasting very sluggish not smooth deacceleration
 
Well turns out this TSB has it's own thread here:

http://www.jeepgarage.org/f107/atten...ore-19418.html

and this is the TSB: http://www.wk2jeeps.com/tsb/tsb_wk2_1801211a.pdf


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