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6 speed coasting question

7K views 24 replies 14 participants last post by  Justinm860 
#1 ·
I have a 2014 SRT Anniversary edition w/6 speed manual and 5.7L.


This transmission has an annoying feature by what seems to be a coast or freewheel spot in the power band. It's especially noticeable when in a light throttle mode in 3rd or 4th when you're in traffic or travelling at low speed and just slightly on or off the throttle. It'll freewheel when you take your foot off the throttle and not brake against the engine compression then engage again.


It'll also do this when decelerating to a stop in any gear, at a certain rpm/speed the transmission will "let go" and the car will coast freely for a brief period then engage again. There's no noise or anything associated with the action and it's very consistent in the way it functions.


I bought this car used from a dealer with 1400 miles on it so it's virtually brand new and has 4500 on it now. I also have never experienced the skip shift issue with 2nd gear I'm reading about, this car has always shifted into second regardless of the speed or whether it was cold or hot so maybe the previous guy had it modified. ???
Can anyone shed some light on this transmission condition? Do they all act like this?
Thanks!
 
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#2 ·
It must have something to do with the electronic throttle control raising the rpm slightly as it will sometimes do, and this rpm is just enough to cancel the deceleration and make it feel like as you describe. It is impossible for the M6 to coast in neutral as you say unless you put it in neutral or push in the clutch, just can't happen by itself on a full manual transmission. On the skip-shift, it will only engage if you try to shift from 1st to 2nd at exactly 20 mph at light throttle, so maybe you are just shifting above or below that point.


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#4 ·
It must have something to do with the electronic throttle control raising the rpm slightly as it will sometimes do, and this rpm is just enough to cancel the deceleration and make it feel like as you describe. It is impossible for the M6 to coast in neutral as you say unless you put it in neutral or push in the clutch, just can't happen by itself on a full manual transmission. On the skip-shift, it will only engage if you try to shift from 1st to 2nd at exactly 20 mph at light throttle, so maybe you are just shifting above or below that point.


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That certainly sounds possible, I have watched the tach when this is happening especially when decelerating to a stop and I really cant see anything different but it could be just enough applied throttle from the computer to make this happen. This is not a once in a while occurrence though it happens every single time I come to a stop and every time I'm in that part throttle area. I was going to set up a service visit and complain about it, maybe there's a cure. ??
 
#3 ·
My Challenger is auto, but I have other cars that are stick. It may be that you are feeling the point where everything is at the same rpm (engine, trans and wheels). In this very narrow window there no pressure on anything in the powertrain. You can actually up shift the trans without using the clutch in that window.

Jeff
 
#8 ·
Not normal, i use engine braking all the time in my 14 srt 6m and it works excellent - i never have the issue you describe. If anything, it get bogged down even more once i hit low rpms and you tend to lurch forward in your seat due to the change in engine braking increasing. I rarely have to use my brakes, i generally just tap them just to warn people behind me that i am slowing down in case they are not paying attention.
 
#11 ·
Really! No kidding, so some cars do it and others don't. Sounds like different versions of firmware in the computer maybe.......


I'm going to set up a service visit for a few things in a while, I'll talk with them about all this and see what they say. Probably the famous "they all do that" answer but at least I have some evidence from you guys that it's not common in most cases. I'll post whatever they tell me.
 
#10 ·
Maybe the bigger 392 engine makes a difference, dunno, but mine kind of throws out the anchor when I slow while still in a higher gear, at least compared to the auto in my Aviator. If I downshift hard without double clutching and rev matching, the tires sound a protest. Seems like she has plenty of compression braking.
 
#15 ·
I think Slidd is correct, the throttle increase must be just enough to give the illusion that it's freewheeling but it's really taking the load off the engine for a brief period when coasting. I'll pay a little closer attention to the tach later and see if I can detect it better.
 
#14 · (Edited)
It has NOTHING to do with the transmission- the transmission does not "let go" at any time unless you press the clutch or take it out of gear.

What you're feeling is the electronic throttle control and/or deceleration fuel cut-off (DFCO). The computer doesn't necessarily close the throttle all the way back to idle when you take your foot off the gas, it may (in certain speed regimes) target a certain throttle percentage or an equivalent no-load idle RPM (in other words, it goes to a a "fast idle" setting that may feel like free-wheeling). I assume this is mostly programmed to minimize emissions because an engine that's at a closed-throttle condition but being spun faster than idle speed by the drivetrain tends to spit a lot of unburned fuel into the tailpipes.... which is where that nice "rapping on the overrun" sound of fuel popping in the tailpipes on vintage cars came from. Challengers will do that *briefly* and then stop... which is a result of either throttle management or Deceleration Fuel Cut-off (DFCO).

DFCO is when the injectors will actually stop firing AT ALL when you're coasting- to save fuel and lower emissions. But it will only do that for a limited time because emissions will go up if it allows the catalysts and combustion chambers to cool down too much- so if you're coasting for a long time- say down a very long hill- you can be in total DFCO (no fuel flow) and then the PCM will re-start fuel flow to keep things warm, and that will feel like a subtle, sudden "freewheel" because the engine drag goes down when the fuel starts flowing again.
 
#17 ·
Hi,
I agree on the transmission comments, it was just a way to try and describe the issue. Thanks for the details and what you're saying makes sense, but I can start off on a flat surface, shift to second gear and take my foot off the gas using the engine backpressure to slow the car and it'll do what I've described. Possibly the computer is being triggered to supply fuel prematurely in an attempt to comply with conditions you describe but are not really present? What do you think?
 
#21 ·
I have a 2014 SRT Anniversary edition w/6 speed manual and 5.7L.
SRT with a 5.7 :scratchhead:.

I've ever noticed that behavior on mine, but I do have an aftermarket tune in it. I know cars at one point had a decel valve that would allow the motor more air so they would coast better in decelaration. In theory for better mileage.
 
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#24 · (Edited)
"I have a 2014 SRT Anniversary edition w/6 speed manual and 5.7L".

You've got yourself a really rare car there, didn't think they made any like that.
 
#25 ·
I have a 2014 SRT Anniversary edition w/6 speed manual and 5.7L.


This transmission has an annoying feature by what seems to be a coast or freewheel spot in the power band. It's especially noticeable when in a light throttle mode in 3rd or 4th when you're in traffic or travelling at low speed and just slightly on or off the throttle. It'll freewheel when you take your foot off the throttle and not brake against the engine compression then engage again.


It'll also do this when decelerating to a stop in any gear, at a certain rpm/speed the transmission will "let go" and the car will coast freely for a brief period then engage again. There's no noise or anything associated with the action and it's very consistent in the way it functions.


I bought this car used from a dealer with 1400 miles on it so it's virtually brand new and has 4500 on it now. I also have never experienced the skip shift issue with 2nd gear I'm reading about, this car has always shifted into second regardless of the speed or whether it was cold or hot so maybe the previous guy had it modified. ???
Can anyone shed some light on this transmission condition? Do they all act like this?
Thanks!
I am dealing with this now. It just started it feels like the car is coasting instead of engine/tranny breaking. You can definitely see that it is using fuel because during deceleration the current mpg will be 100+. But then after a few seconds may be like 20 or so the current mpg will drop down to like 17 while decelerating. It feels like it’s coasting or on cruise control it’s very annoying and killing my mpg.
 
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