Question regarding transmission behavior

[bdbake01]

I have a 4x4 AT w/ 6.2L here. I only have about 2k miles on it, but I've noticed something interesting with the tranny behavior. If I'm coasting to a stop, somewhere around 30 ~40 mph it feels a bit like the engine begins braking. I'm not talking about hill/grade braking, I've seen that kick in and it's rather pronounced and has an associated DIC notification. This is subtle, but there. I can feel the engine/tranny dragging a bit seemingly slowing the truck. Is this normal/expected? Previous vehicles of various sorts all seemed to free wheel a lot more in this range.

[MMC]

Normal, I take advantage of it in snow or ice conditions you don't need to break much at all.

[fondupot]

Yes. This is normal. I cant remember what it's called, but its a fuel saving feature, instead of freely coasting and having to supply fuel to keep the motor, these new engines have a fuel shut off feature where when you are off the gas and coasting, no fuel is being used. Instead the wheels are driving the motor. So what you are feeling is the road speed.

 

You get used to it after a while.

 

I hope that makes sense.

[bdbake01]

Ok. This is pretty much what I was assuming, but it still feels a bit unusual. I guess it is unusual in that it's a relatively new "feature" or operating mode. Thanks for the feedback!

[iCryWheniGoPoop]

It's called "deceleration fuel cut off" or DFCO. Cuts fuel and timing after certain criteria are met in the ECU, causing the slight engine brake that you are feeling.

[fondupot]

It's called "deceleration fuel cut off" or DFCO. Cuts fuel and timing after certain criteria are met in the ECU, causing the slight engine brake that you are feeling.

 

There it is!

[GMC-AT]

and it sucks IMO... I don't have any issue with the Active Fuel Management .. put I can't get used trans and coasting behavior.

[bdbake01]

It's probably a great thing for mpg, but I'm kinda with GMC-AT here. It's just such an odd feeling to me. Seems like I'm burning the tranny's overrun clutches!

[KARNUT]

Could all ways downshift your self, have some fun with the rev matching.

[iCryWheniGoPoop]

It can be shut off for the guys that are getting tunes, I can turn mine off anyway. It would take me longer to hook up my laptop that it does to toggle it off in the calibration.

[MotoMedic]

It also reduces wear on brake rotors/pads.

 

It took me about 6 months to get accustomed to it... now I rarely notice.

[iCryWheniGoPoop]

I personally keep mine on, but being that I am somewhat of an aggressive driver, I rarely encounter the engine braking. I have noticed it more lately though as I start driving like an adult again but I don't see how it is negative in any way, unless you just like coasting. Its not an aggressive engine braking, its very subtle and I seriously doubt it puts any excessive strain on the drive train. I would hate to see what some of you guys were to say if you bought an Allison.

[bdbake01]

I personally keep mine on, but being that I am somewhat of an aggressive driver, I rarely encounter the engine braking. I have noticed it more lately though as I start driving like an adult again but I don't see how it is negative in any way, unless you just like coasting. Its not an aggressive engine braking, its very subtle and I seriously doubt it puts any excessive strain on the drive train. I would hate to see what some of you guys were to say if you bought an Allison.

 

Oh I'm with you. It is subtle, not much at all. Certainly nothing like the "grade braking" when it kicks in. Still, if you're not expecting it, it kinda seeems like the tranny is holding gear too long. Which, I guess it is compared to, say, an old powerglide

No no keep discussing I was just referring to my post. I had asked a question about being able to tune this feature out with a tune but I saw that had TDT answered my question once I hit the submit button. I only wished to delete my post not the thread. My apologies for my miscommunication.

 

Ah, no worries! Sorry to sound defensive!

[iCryWheniGoPoop]

 

Oh I'm with you. It is subtle, not much at all. Certainly nothing like the "grade braking" when it kicks in. Still, if you're not expecting it, it kinda seeems like the tranny is holding gear too long. Which, I guess it is compared to, say, an old powerglide

 

 

 

Correct, it is quite a bit more pronounced that the old 2 speed, especially since it did not have a lock up converter and wasn't capable of such newfangled nonsense.

[boxerbull]

I have a the 4.3 would my trans be the same? I was going to bring it in because it seems like from about 30mph down to 20mph there is a slight vibration almost like when your driving a manual trans and your in to high of a gear but not as pronounced as it would be in a manual trans. this is the second truck i have bought in a year and i had small issues with the other one too so i am loosing faith but if its designed to be that way it makes me feel better.