Low Engine RPM Transmission Rumble

[jdvaughn]

Hey Guys,

I am not here to complain about the quality of the vehicle, but rather ask a simple question to see if others are experiencing the same thing as I am with my truck. I like the truck regardless of the stupid things I hate and want to work through the bugs to make this thing 110%.

 

Anyways, I am at 6k miles and it seems that when I am driving on a flat road or a sight incline (no declines) at approximately 45 mph and the transmission has shifted up to 6th I seem to experience a slight rumble in the truck that seems to be trans related. If I stay away from that engine speed (Just over 1100-1200 rpm) it doesn't do it, but the second I let it shift up to 6th at 45 mph I seem to feel it come on.

 

Not sure if it is the torque converter locking up too early? If I go into tow/haul mode or manual to stay a gear higher then once again it doesn't take place. It seems it is related to the 1100-1200 engine rpm and 6th gear in the trans (~45 mph vehicle speed with 3.42 gears). I think I have seen one or two posts about someone having an issue with a torque converter on these trucks and the RPM/tach float that occurs when driving at a constant speed up a slight grade and was hoping someone could maybe shed some light on this. My RPMs seem to float a litte on constant speed up hill grades indicating that the torque converter may be loading and unloading?

 

I saw a post by someone stating you can supposedly pull the whole fuse box in one swipe and reset the TCM, but not sure if that actually works. I would be surprised if the TCM memory wasn't non-volatile memory(meaning it wont be lost if the power is lost/fuse box pulled),but hey if it has worked for others I may give it a shot. Any advice on this is appreciated!!!

[gone_fishing]

This sounds like what I was experiencing: http://www.gm-trucks.com/forums/topic/155198-rpms-fluctuating-when-accelerating-under-light-load/?do=findComment&comment=1374485

 

I'm pretty sure this issue is computer programing related. I wonder if we could get GM's attention on this matter.

[scooby5121]

Factory Setting for the 6 speed.... are exactly that.... Crappy.

Lots of threads about Transmission Surfing, etc.

My 08 had a Transmission update. Only if you wanted it and complained about how and when it shifts. There is a TSBulletin for the transmission back in 08.

Engine and Transmission Tune WILL FIX IT.

[scooby5121]

There is a service bulletin, my service manager
printed and gave it to me. They are all aware of the problem but
refuse to fix it. Apparently GM had to increase the average gas mileage
of all trucks so they made the 6 speed and have it shift prematurely to
lower engine speed and increase the mileage.

 

taken from another posting

[jdvaughn]

Gone-fishing

It sounds just like what your post was stating. Seems it js shifting early to try and maximize fuel. The issue is that running at low rpm under load can actually be less efficient, hence more fuel than a lower gear might be.

 

Anyone with a transmission tune that installed the tune and alleviated this issue? Any recommendations?

[jdvaughn]

There is a service bulletin for this issue on a 2014?

[jdvaughn]

Anyone tried to (and successfully) reset the tcm by pulling thr fuse box as I have seen in another post or two?

[scooby5121]

Gone-fishing

It sounds just like what your post was stating. Seems it js shifting early to try and maximize fuel. The issue is that running at low rpm under load can actually be less efficient, hence more fuel than a lower gear might be.

 

Anyone with a transmission tune that installed the tune and alleviated this issue? Any recommendations?

I have the tune and yes it is perfect..... Engine and Tranny program from BR Performance, In Oakville. Ont.

Everyone else has A Black Bear tune... they are one of the sponsors here.