Upgrading your vehicle with an LS engine swap often requires careful consideration of the Powertrain Control Module (PCM) and its tuning. This article addresses common transmission issues encountered after an LS swap, specifically focusing on PCM tuning solutions for a 4L60E transmission in a BMW using a replacement 0411 PCM from a 2002 Suburban.
Understanding the Problem: Erratic Shifting Behavior
After swapping a 4896 PCM (OS 12212156) with an 0411 PCM (OS 12216125) in an LS swapped BMW, erratic transmission behavior was observed. The engine runs smoothly with the existing tune, but the 4L60E transmission exhibits unpredictable shifting patterns. Symptoms include:
- Random Gear Selection: Upon starting, the commanded gear jumps erratically between gears 1 through 4 without any discernible pattern.
- Premature Upshifting: While driving, the transmission shifts up through the gears far too early.
Troubleshooting steps already taken include:
- Hardware Replacement: All transmission solenoids and the pressure manifold have been replaced.
- Electrical Verification: Wiring connections from the PCM connector to the solenoids and pressure manifold switch have been confirmed to be sound.
- Park/Neutral Switch: A functioning P/N switch on the shifter grounds pin 34 when in Park or Neutral.
Despite these efforts, the problem persists, leading to the suspicion of a faulty PCM potentially grounding the transmission solenoids unintentionally. This malfunction seems to occur only when the engine is running.
PCM Tuning Solutions: Transferring and Refining the Tune
To address this issue, two primary PCM tuning options are being considered:
Option 1: Direct Tune Transfer
This involves a “Write Entire” process to transfer the existing tune from the old 4896 PCM to the new 0411 PCM. This approach raises the question of whether a direct transfer will effectively resolve the issue or if underlying problems within the tune itself might be contributing to the transmission problems.
Option 2: Stock Tune with Manual Adjustments
This method involves using the stock tune within the new 0411 PCM as a baseline and manually adjusting the engine parameters to match the existing tune. This approach allows for isolating potential issues within the transmission control portion of the original tune. By leaving the transmission controls in their stock configuration, it provides a controlled environment to diagnose if the original tune’s transmission settings are corrupt or causing the erratic behavior.
Conclusion: Finding the Right PCM Tuning Strategy
Ultimately, choosing the correct PCM tuning strategy depends on determining the root cause of the transmission issues. If the problem stems from the original tune, Option 2 offers a safer approach by allowing for a controlled comparison with the stock transmission settings. If a direct tune transfer is chosen (Option 1), careful monitoring and potential further adjustments may be necessary. Both options highlight the importance of a thorough understanding of PCM tuning when undertaking engine swaps and addressing complex transmission problems.
