Urgent Help: 2013 SRT8 6.4L LTFT Issue & Power Loss after Mechanical MDS Delete (Diablo T2 EX)

[JxS]

Hello all,

I'm hoping someone can help me diagnose a potential tuning or mechanical issue after an MDS delete. My engine lost noticeable power after the modification and subsequent tune.

Vehicle: 2013 Jeep Grand Cherokee SRT8 (WK2) with the 6.4L Hemi. Tuner: DiabloSport Trinity T2 EX. Tune Used: Stock Tune modified only to electronically disable MDS. Hardware Mods: Only a Mechanical MDS Delete Kit was installed on the motor.

The Issue: The motor is suffering from noticeable power loss, is running rough, and sounds like it is running on four cylinders at idle, even though the MDS is mechanically and electronically disabled. The fuel trims are significantly out of spec.

Current Data:

LTFT Readings (At Idle): I'm seeing heavily out of range LTFTs on both banks.(Need to update values)

Exact Values/DTCs: I will be logging and posting the exact LTFT/STFT values and any stored Diagnostic Trouble Codes (DTCs) first thing tomorrow morning.

Troubleshooting So Far:

I suspect the tune is not properly compensating for the mechanical MDS delete. I have visually inspected for vacuum leaks around the intake and the new MDS block-off plates, but a thorough check is next.

Questions for the Forum:

Given the out of range LTFTs and the sound of a severe misfire (or 'V4 mode' sound): Does this immediately point to a major vacuum leak introduced during the MDS kit installation, or is this a known severe tuning compensation issue for the 6.4L Hemi after this mod?

Assuming I confirm the out of range LTFTs tomorrow, what Diablo fuel table (e.g., Idle/Cruise) is the best place to start adding fuel percentage to correct the lean condition?

Thank you in advance for any initial thoughts—I'll update the thread with the exact numbers and codes tomorrow!
Codes:
P0300
P0172

[mikel]

this is almost never tune related and almost always mechanical.
all we do is flip a switch to tell the pcm its not equipped with MDS, and its gone. Post the Last tune written from the tunes folder, and we can confirm that.

Beyond that, its usually an install issue, or pushrods too long, valves not fully seated, something unplugged, etc.

Remember, if idling, it would not be trying to engage MDS, so even the stock tune should work fine to idle it. If it still has misfires and a rich code, you have a mechanical or install related issue.

[JxS]

Thank you very much for the immediate feedback. Given the severe running issues (P0300 Misfire and P0172 System Too Rich - Bank 1) and your expertise that this is almost never tune-related, I am now focusing entirely on the mechanical side of the MDS delete installation.

As requested, I have attached my "Last Tune Written" file for you to confirm the electronic MDS disable switch is active and correct. I also included some logs that specify the values.

[mikel]

I can confirm the only change in the tune file is MDS disabled.