Non linear acceration from deadstop

alkaspeltzar · March 17, 2017

So I have noticed in my 2014 Silverado, 5.3L, 3.42 gears, 68K miles, that at times from a dead stop, without any change to throttle input, I get a non linear acceleration.

It is like I put my foot into the pedal but don't move it, the truck accelerates normally but then has a little extra bump at the end.

Some of the posters in the thread below mentioned something similar and I am trying to determine if anyone else notices this, knows why my truck is doing this, and is it okay?

http://www.gm-trucks.com/forums/topic/175595-slow-speed-uncommanded-acceleration/

Thanks

michigan2500hd · March 17, 2017

Could it be related to the"floating" gas pedal assembly? I'm planning on fixing mine this weekend. It has way too much flex and wiggle. Very 'tarded engineering.

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alkaspeltzar · March 18, 2017

No it's not the pedal. Mine doesn't have much play and I'd feel it move.

Try taking off at a light dead stop, with moderate throttle input. Too heavy you break tires free. Too little and truck is a tortoise. With moderate input, no movement in foot, it will accelerate as if I am putting my foot into it.

qwank · March 18, 2017

torque management

jerniganbrandon · March 19, 2017

It's the turbo spooling up

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brawls · March 19, 2017

My 2014 5.3L with 3.42 gears (bought new) has always exhibited a similar trait. On acceleration, at certain speeds it's as if the engine sounds like it's trying to figure out whether to increase or decrease rpm's. I thought maybe it was the variable valve timing, but maybe it is the torque management. In any event it's a bit weird, very unlike my old '97 Vortec 5.7L.

TxTruckMan · March 19, 2017

There's no cable going to your TB. It's controlled by your ECM, so you won't get linear acceleration from a stop to protect your drive line = torque management.

GM has had this for nearly 2 decades now.

Newell33 · March 19, 2017

There's no cable going to your TB. It's controlled by your ECM, so you won't get linear acceleration from a stop to protect your drive line = torque management.

GM has had this for nearly 2 decades now.

Nope. Not the same. My '14 had the same issue, and none of my previous trucks exhibited this characteristic. It's another example of poor programming.

KARNUT · March 19, 2017

I had to look it up linear is straight or straight line just as I thought. So every vehicle I own or have owned went straight when I hit the gas. The only exception is when some may kick out the back end a bit when I smoke them down, but straight is the overall objective. So linear may not be the right word.

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CounterMeasure · March 20, 2017

No, linear is the correct word. Go back to your days in school where you graphed out a line. If the line has a constant slope, then its linear. If its curved, its non-linear. And your description of driving direction is not the same as what is being asked here.

In this case, if you hold the pedal steady at say 20%, then you expect a constant increase in RPMs, giving smooth acceleration, thus a linear line if you plotted it out of pedal position to change in RPMs. But that's not what happens. At a point in the RPM band, the RPMs start to increase more on the way to shifting to second gear, so you get more acceleration at a constant pedal position as if you were gradually adding more pedal the fast you were going. If you graphed it out, the line would be curved, or non-linear.

Its the first vehicle I've owned that does this. My belief is its programmed this way for torque management and to allow a high enough RPM to give a smooth-ish shift into 2nd gear.

I had to look it up linear is straight or straight line just as I thought. So every vehicle I own or have owned went straight when I hit the gas. The only exception is when some may kick out the back end a bit when I smoke them down, but straight is the overall objective. So linear may not be the right word.

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njk4o5 · March 20, 2017

another case of the crappy stock gm transmission tuning

TxTruckMan · March 20, 2017

It's not the transmission. There was a video years ago on You Tube that showed how the throttlebody works on GM V8's. When you push the gas all the way down, the TB does not go to WOT instantly. It delays for a few seconds. There are mods available to bypass this, though I don't know if they work for our trucks. GM is trying to prevent you from damaging the engine/tranny to get more longevity out of the driveline. The surge you feel after a couple of seconds is probably the TB finally opening all the way.

Also, you're correct about the non-linear peddle response on these trucks. You have to push down much further on the gas to get the same amount of GO from previous years. When I first got my 2014 it took me a while to adjust to it. On my previous truck, 50% throttle got me 50% acceleration. On my 2014, 50% throttle got me 25% acceleration. You need to press down further on the gas to get your expected response.

And it's not crappy programming, it's GM's response to CAFE to achieve better fuel economy and to protect your drive line from damage.

Newell33 · March 20, 2017

This issue was new in the '14 body style 1500 trucks. This is not a torque management issue during shifting. It's an issue while the truck is accelerating in a specific gear. This is absolutely a programming issue.

TxTruckMan · March 20, 2017

This issue was new in the '14 body style 1500 trucks. This is not a torque management issue during shifting. It's an issue while the truck is accelerating in a specific gear. This is absolutely a programming issue.

It's probably not new, but more exaggerated with the new trucks. In first gear from a dead stop you get reduced power for a few seconds. Not transmission torque management specifically, but another way to protect the engine.