RPM flare/surge when in cruise, w/ & w/out shudder

[joeb123joeb]

When going down highway, cruise set at 69, my rpms will flare sometimes. Will be about 1500 rpm and then will flare up about 50-100 rpm quick and go back down to 1500rpm. You can hear change in exhaust tone when it happens. Also, sometimes i get a shudder/vibration when the rpm flares, but other times i dont. Any ideas? TIA

[davester]

I would use a scanner to log live data, to see what's happening with the transmission, if the torque converter is unlocking or if it's downshifting briefly.

[m3n00b]

#MeToo

[HeySkippyDog]

Does it happen on an uphill grade, even a slight one? You might be right on the edge of a shift point.

Sent from my SM-J810F using Tapatalk

[joeb123joeb]

47 minutes ago, HeySkippyDog said:

Does it happen on an uphill grade, even a slight one? You might be right on the edge of a shift point.

Sent from my SM-J810F using Tapatalk
 

Can happen anytime, can be flat or a little uphill.

 

10 hours ago, davester said:

I would use a scanner to log live data, to see what's happening with the transmission, if the torque converter is unlocking or if it's downshifting briefly.

Any recommendation on a scanner?

[davester]

I would suggest something like Autogenuity w gm enhancement, or a knockoff of whatever gm is using now in place of a tech ii (they use a newer, different device now, I don't believe tech ii's work with newer trucks like yours).

[ksiesel]

16 hours ago, joeb123joeb said:

When going down highway, cruise set at 69, my rpms will flare sometimes. Will be about 1500 rpm and then will flare up about 50-100 rpm quick and go back down to 1500rpm. You can hear change in exhaust tone when it happens. Also, sometimes i get a shudder/vibration when the rpm flares, but other times i dont. Any ideas? TIA

Sounds like you are switching between V4 and V8 modes.  The TC unlocks for each transition between the two as I’ve noticed this on my truck too.

 

Watch the Fuel Economy screen in your truck on your next drive.  It should have an indicator for V4 and V8.  I bet that moments after you see the “flare”, you’ll see a shift from V4 to V8 or vice versa.

[joeb123joeb]

1 hour ago, ksiesel said:

Sounds like you are switching between V4 and V8 modes.  The TC unlocks for each transition between the two as I’ve noticed this on my truck too.

 

Watch the Fuel Economy screen in your truck on your next drive.  It should have an indicator for V4 and V8.  I bet that moments after you see the “flare”, you’ll see a shift from V4 to V8 or vice versa.

I thought that too, but i looked to see if that was it and it wasnt