2019 Yukon Stumble / Misfire, no codes

5.3 6 speed with 80,000 miles.
At light throttle there is a noticable stumble that smoothes out with RPMs.. no codes thrown.
Just changed the plugs and wires - they were shot. feels like it runs a little better, but the stumble is still there. Based on some forum posts, I decided to change the MAP sensor.
No improvement. Cleaned the MAF sensor, no improvement. Cleaned the TB, no improvement.

Misfires are on one or two cylinders at a time, sometimes on the same bank, sometimes on both banks.
Misfire count is usually 2-3 before it smoothes out.

I've attached an HP Tuners log file of a test drive.
At first glance, it looks like the upstream O2 sensors are a bit lazy.. but I'm far from an expert.

Can someone clue me in what to look for on the logs that would be a smoking gun as to what's actually up with this thing?

So you're logging misfires but not enough to set a code, correct?

I suggest doing a CASE relearn to at least rule it out; sometimes that clears up mysterious misfires. Can be done with a decent bidirectional scanner.

mecheng76 said:

Can someone clue me in what to look for on the logs that would be a smoking gun as to what's actually up with this thing

Click to expand...

I have HPT but can't unzip this file with chrome OS, and my HPT laptop no longer has a wifi antenna. I don't use it in internet....HPT & Power Commander only

But regardless I think you would have better chance getting help w/this on the HPT forum... Not bc members here cant or wont help! Just very few of us w/HPT

But you don't even need that... You have the ability to log and live watch your engine data! There are only a few things that can cause a misfire.

Look at cylinders that are misfiring, lets say it's #2. Swap the coil pack on #2 with the coil pack on any cylinder that has 0 misfires and see if the misfire follow the coil pack? If so, you prob need at least 1 coil pack. Could also be the plug on that same cylinder...
If misfire doesn't follow coil pack, then swap the spark plug with a cylinder that has 0 misfires.
if there's more than one cylinder misfiring isolate them and eliminate one possible cause at a time, Write down what you do as you go
If it's not any of the coil packs or any of the plugs, then try the injectors. Follow some good instructions to relieve pressure on the fuel rail and remove injectors.
Then remove the injector from the cylinder misfiring.
*TIP- You can use some alligator clips and or small magnets to hook injector up to 9V battery and spray some carb cleaner through it. Should see 4 evenly spaced cones of mist coming through.. Once cleaned reinsert it go for another drive...

I'd be stunned if it turns out to be anything other than one of these three components... But even then, you have what you need to solve the problem

Good luck