Stumble at part throttle, no codes: It's the torque converter

[John H Daniel]

My 2011 Denali has started an annoying stumble at part throttle.
So under light load, in any gear, with just enough throttle to accelerate, but not shift down, the engine will stumble/miss/hesitate. Down shift to higher revs, its smooth, no problem.
I noticed it first while towing; when cruise control is trying to add speed before needing to down shift.
No codes, fuel pressure is good, new plugs, air filter; tried injector cleaner, cleaned throttle body, checked for vacuum leaks.

Any ideas?

 

[Geotrash]

My 2011 Denali has started an annoying stumble at part throttle.
So under light load, in any gear, with just enough throttle to accelerate, but not shift down, the engine will stumble/miss/hesitate. Down shift to higher revs, its smooth, no problem.
I noticed it first while towing; when cruise control is trying to add speed before needing to down shift.
No codes, fuel pressure is good, new plugs, air filter; tried injector cleaner, cleaned throttle body, checked for vacuum leaks.

Any ideas?

How many miles on it?

 

[John H Daniel]

198,000. I've had it last 20,000.

 

[Doubeleive]

Might be time for a new maf, also cleaning the throttle body does not always fix all issues they wear out, mine was doing something similar and I changed the throttle body to a ls3 type since I was replacing it anyway and the problem went away

 

[Fless]

Have the accelerator pedal position sensor and the throttle position sensor been graphed (for smooth tracking) and compared?

 

[John H Daniel]

Have the accelerator pedal position sensor and the throttle position sensor been graphed (for smooth tracking) and compared?

No

 

[Geotrash]

+1 for the MAF.

 

[gpracer1]

Could be all those ideas but you will need scanner of some sort to log data. If it were me I would watch the O2 sensors switching and then see if either or both banks react to the problem happening. That way you can rule out one side or common sensor.

 

[2K8Lade]

+1 for the MAF.

Any way to tell if it's bad? I'm still trying to figure out my issues and I saw the MAF readout of like .10 to .17 lbs/s or something like that. No idea what the normal number is.

 

[John H Daniel]

I went after the ignition and intake stuff many folks have done. Nothing helped.
With more research, I settled on the torque converter shudder/ failing TC/ lockup clutch.
I was hoping to just replace the TC, but was concerned that its failing many have shed metal particles. So I connected a hose I use to change fluid to the trans oil cooler and pumped out a cup or so.
Yep, metal in the cup.
So rebuilt trans, TC and are about to happen. Good time to replace that leaking rear main seal as well.