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RPMs fluctuating when accelerating under light load???


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This is something I thought I picked up on earlier so I spent some time tonight driving around trying to replicate it. This is somewhat difficult to explain so I'll do my best. First I will get up to about 40 MPH which is around 1200 RPM's. The transmission is in the highest gear it would be for this speed. After maintaining this speed and throttle, I'll apply a little more throttle (not enough to drop a gear) and the RPMs will come up but not smoothly. I can see the tach needle almost 'bobble' a little while under this light load. I would say it's a fluctuation of about 50-100 RPMs. I did note that this was not during a V4 to V8 transision when accelatoring (already in V8). Engine was already up to operating temp also.

 

Has anyone else observed this? If not, it would be interesting if others could try to replicate what I just explained.

 

I've had this truck for 3 weeks now and just can't seem to get really used to this throttle. Not only does it seem heavy but when taking off from a start, its always feels like the first bit of throttle movement doesn't really do anything. Then after what feels like a lot of throttle pushing, the truck comes "alive" and get's going. Coming from my 2010 Tundra 5.7 the throttle was very smooth and not heavy at all. My 2005 Honda Accord also has a very light and smooth throttle. I can adapt to the feel of throttle but the flucuating RPMs concern me a little.

 

Thanks

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Probably won't make you feel better, but the current (LML) duramaxes also have a very 'flat' response to initial throttle movement. I found that once used to it other throttles seem overly touchy.

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Mine did this and I originally thought it was the torque converter slipping or kind of grabbing and letting go constantly. Since I have gotten my trinity though it seems to have gone away and I haven't touched any converter lock options yet. My guess is it's the throttle body doing something weird because as I was cruising in 6th and not changing my foot at all, I could see on my dashdaq that the throttle position was going up and down with the rpms (before tuning).

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That sounds like pretty normal torque converter stuff with a factory tune. Modern converters don't lock up like flipping a switch, they're pulse width modulated so the computer can lock it up to varying degrees. With a typical factory tune, just a small increase in throttle while cruising can cause the computer to unlock the converter to some degree. And the factory tunes usually make the engagement/disengagement slow, gradual and mushy so you never really feel it happening but if you watch the tach you can see something's going on.

 

Tuners often remove much of this making the converter lockup feel much more like another gear shift and limiting when it occurs.

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  • 7 months later...

My 2014 does this, and my 2010 did it. I was hoping it would be fixed....anyone out there see this and should I worry?

 

Dealer seems to think it is all normal, part of AFM and shift management.

 

Shift management kinda makes sense. My guess is since the transmission isn't slipping in lower gears or at higher speeds, such as 70mph, but only around 40-50, the transmission is trying to determine if it should shift or partially slip for additional torque, hence the objective of shift management as per the manual.

 

Looking for some piece of mind, I had to trade the 2010 for continual tranny problems, mainly failure to slamming gears/high internal pressure. I am hoping the 2014 is a different beast that will last.

 

Thanks for any and all help

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My 2014 does this, and my 2010 did it. I was hoping it would be fixed....anyone out there see this and should I worry?

 

Dealer seems to think it is all normal, part of AFM and shift management.

 

Shift management kinda makes sense. My guess is since the transmission isn't slipping in lower gears or at higher speeds, such as 70mph, but only around 40-50, the transmission is trying to determine if it should shift or partially slip for additional torque, hence the objective of shift management as per the manual.

 

Looking for some piece of mind, I had to trade the 2010 for continual tranny problems, mainly failure to slamming gears/high internal pressure. I am hoping the 2014 is a different beast that will last.

 

Thanks for any and all help

Try putting your truck in M5, A few of us here have notice better manners out of the trans. when doing this. It keeps it from going to V4. I don't click up to M6 unless I going to do 60MPH or better for a while. My in town fuel mileage hasn't been affected and you don't get that jumping around feeling. Even with the can tune Im using it just seems like it hits 6TH gear way to soon.
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I can try M5, and it does seem to help as it is not a high of the gear. But I know when I am seeing this the truck is already in V8 mode, not switching to V4.

 

So it begs the question, why is the truck partially slipping at this speed/load? It doesn't do it any other time.

 

Is it normal and a normal function as the original poster asked?

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I can try M5, and it does seem to help as it is not a high of the gear. But I know when I am seeing this the truck is already in V8 mode, not switching to V4.

 

So it begs the question, why is the truck partially slipping at this speed/load? It doesn't do it any other time.

 

Is it normal and a normal function as the original poster asked?

It appears that you resolved your question in your own post, I was adding that the trans seems to hit 6 speed to soon which would cause fluctuation in the RPM. I doubt that you are keeping exact pressure on the go pedal so your truck is reacting to your impute. If your trans is slipping, in no time it will get worse.
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KARNUT, do you see it on yours? That is what I want to know, can others see this happening?

 

 

Looks like between pedal sensitivity zoning at lower speeds, to AFM to shift management partially slipping TCC for additional torque without changing gears, that is what I am seeing. Must be a load that induces it at 40-50...probably because its in 6th gear and there is no power there.

 

That is why I drive from 0-60 in M5, then switch to drive(6th) when on highways.

 

Thank guys! Really appreciate it

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KARNUT, do you see it on yours? That is what I want to know, can others see this happening?

 

 

Looks like between pedal sensitivity zoning at lower speeds, to AFM to shift management partially slipping TCC for additional torque without changing gears, that is what I am seeing. Must be a load that induces it at 40-50...probably because its in 6th gear and there is no power there.

 

That is why I drive from 0-60 in M5, then switch to drive(6th) when on highways.

 

Thank guys! Really appreciate it

Yes, every automatic transmission I have ever owned from power glide on. It in the converter any way not the trans, unless something change while I wasn't paying attention. Edited by KARNUT
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There is a hill on my way home from work. 50 mph zone, my truck pulls it 6th at 1500 rpm, pulses like you are describing every time.

Annoying, but it doesn't appear to hurt anything.

Edited by Moldman
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There is a hill on my way home from work. 50 mph zone, my truck pulls it 6th at 1500 rpm, pulses like you are describing every time.

Annoying, but it doesn't appear to hurt anything.

Thank for all the help all. It is nice to know others see this too and it is just the tranny doing its thing.

 

I talked to the dealer and they said with the 6 speed and the Shift/Torque management system, the tranny will lock up and release at times depending on load to be in the best possible gear for fuel economy. It is normal.

 

I also noticed in M5, keeping the truck out of 6th until higher speeds are obtained, this issue goes completely away and the tranny stops fishing around for gears.

 

Lastly, I noticed the truck seems to have calmed down. I was told it may need to learn driving habits....even when it is in 6th gear at low speeds, it does it little if any, like it learned to hold the gear, or downshift. All I know is this baby is running great and I love it so far. Hope the next 200,000miles are this good.

 

Thanks again!

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