Weird vibration / rough engine - no codes - pulling my hair out!

[Holmes]

Please Help with ideas:
2019 Mustang GTPP1
93 octane tune.
100% track set-up, pretty much everything in the Steeda Catalog.
Just had Diff rebuilt, drive shaft carrier replaced, new GT350 half Shafts installed.
Car was in the shop a long time and the techs drove it a lot “testing” so they say….different shop did my diff rebuild vs my normal guys. Diff rebuild shop said the roughness was due to my solid motor mounts, but it was never this rough before.
Car cranks easy, never stalls, puts down good power, lap times and track speed/acceleration data from the track computer looks good and consistent with prior performance.
But, I’ve got this bad roughness/vibration when under power. Most noticeable at around 2.5K rpm and 5.5K rpm. The roughness is always there. Even at startup and idle it feels rough, sort of out-of-balance, you can feel more roughness at around 2.5K and around 5.5K rpm. At any speed I can push in the clutch and when the rpm drops the roughness goes away, or at least is much less noticeable. If I didn’t know better, feels like a cylinder is missing, but no codes, power is good.
Any ideas what to check?
Thank you!

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[MrMike]

Any chance they didn't mount the driveshaft in the most balanced position after dropping and putting the diff back up?

 

[Holmes]

Was initially thinking that but roughness seems to be RPM related, not speed related. When clutch is pushed in, rpms drop, vibration is much less noticeable. Was thinking if it was the driveshaft vibration would get worse with speed. Now, having said, along with the diff rebuild we did install a new one piece driveshaft. After that, at or above 90mpg it felt like the car was going to shake itself apart. Felt like riding an unbalanced washing machine. Had my shop take the one piece DS off and put the two piece back on along with a new carrier. Now the “washing machine” shake is gone but this rpm related roughness is still there. Maybe two separate issues. Maybe the bad shake caused/exposed another problem with the transmission or engine?

 

[Holmes]

Was initially thinking that but roughness seems to be RPM related, not speed related. When clutch is pushed in, rpms drop, vibration is much less noticeable. Was thinking if it was the driveshaft vibration would get worse with speed. Now, having said, along with the diff rebuild we did install a new one piece driveshaft. After that, at or above 90mpg it felt like the car was going to shake itself apart. Felt like riding an unbalanced washing machine. Had my shop take the one piece DS off and put the two piece back on along with a new carrier. Now the “washing machine” shake is gone but this rpm related roughness is still there. Maybe two separate issues. Maybe the bad shake caused/exposed another problem with the transmission or engine?

Also if just sitting still and reving the engine in neutral, I can tell there is a roughness. It’s more noticeable under a power load when moving down the road or under any type of acceleration or just maintaining a constant speed. Push the clutch in at any speed, roughness gets much less noticeable. I did about 16 laps total at the last track event then got worried that I would break something or cause damage if I kept running it with the roughness. Plus it’s no fun when the car is vibrating like this. My GT350 by comparison feels almost like an electric car, it’s so smooth.

 

[sms2022]

Sounds like a glitch between the DI transition at least at low rpm. Could be a small vacuum leak too. Have you tried just resetting the keep alive memory for the ECU though?

 

[K Myers]

Please Help with ideas:
2019 Mustang GTPP1
93 octane tune.
100% track set-up, pretty much everything in the Steeda Catalog.
Just had Diff rebuilt, drive shaft carrier replaced, new GT350 half Shafts installed.
Car was in the shop a long time and the techs drove it a lot “testing” so they say….different shop did my diff rebuild vs my normal guys. Diff rebuild shop said the roughness was due to my solid motor mounts, but it was never this rough before.
Car cranks easy, never stalls, puts down good power, lap times and track speed/acceleration data from the track computer looks good and consistent with prior performance.
But, I’ve got this bad roughness/vibration when under power. Most noticeable at around 2.5K rpm and 5.5K rpm. The roughness is always there. Even at startup and idle it feels rough, sort of out-of-balance, you can feel more roughness at around 2.5K and around 5.5K rpm. At any speed I can push in the clutch and when the rpm drops the roughness goes away, or at least is much less noticeable. If I didn’t know better, feels like a cylinder is missing, but no codes, power is good.
Any ideas what to check?
Thank you!

All the mods are going to increase your NVH, but I would start with the drive shaft

 

[Eyesac]

I'm voting for bad dual mass flywheel. I had vibrations that started at about 2k and went to redline. It was noticeable, but not too alarming and happened for a pretty long time with no other issues and then quickly got much worse one random morning. No CEL, no stored codes.

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