Maintaining optimal engine timing is crucial for the performance and longevity of your 6.5 diesel engine. The Top Dead Center Offset (TDCO) is a critical parameter that the engine control module (PCM) uses to manage fuel injection timing. When the TDCO is not correctly learned or set, it can lead to issues like poor fuel economy, increased engine noise, and reduced power. This guide provides a detailed walkthrough on how to perform a 6.5 Obd2 Tdco Learn procedure, often referred to as the “KoKo” method, ensuring your engine runs smoothly and efficiently.
Understanding TDCO and Its Importance
TDCO, or Top Dead Center Offset, is essentially the fine-tuning of the injection pump timing in relation to the engine’s crankshaft position. The PCM needs to accurately know this offset to deliver fuel at precisely the right moment for optimal combustion. Factors like injection pump replacement or timing adjustments can necessitate a TDCO relearn. Without proper TDCO learning, the PCM may rely on incorrect data, leading to suboptimal engine performance.
The “KoKo” TDCO Learn Procedure: Step-by-Step
The “KoKo” method is a manual procedure to initiate the TDCO learning process using the vehicle’s accelerator pedal and ignition key. It’s a practical approach when you need to ensure the TDCO is correctly relearned, especially after mechanical adjustments to the injection pump.
Here’s how to perform the “KoKo” TDCO learn:
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Prepare Your Vehicle: Ensure your 6.5 diesel engine is at its normal operating temperature. Clear any Diagnostic Trouble Codes (DTCs) using an OBD2 scantool. It’s also wise to use the scantool to note the initial TDCO value as a baseline for comparison.
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Key On and Pedal Depress: With the engine off, turn the ignition key to the “ON” position (without starting the engine). Fully depress the accelerator pedal and hold it down for at least 45 seconds. This step allows the PCM to prepare for the TDCO relearn process.
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Key Off and Memory Clear: Turn the ignition key to the “OFF” position and leave it off for a minimum of 30 seconds. This crucial step allows the PCM to fully power down and clear its memory, including any learned driveability parameters. This ensures a clean slate for the TDCO relearn.
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Engine Start and TDCO Relearn: Turn the ignition key back to the “ON” position and start the engine. The TDCO relearn process will automatically begin as soon as the Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) reach operating temperatures. You might notice a slight engine hesitation or increased engine rattle as the PCM actively seeks the correct injection pump position. If the timing is already close to correct, these symptoms may be minimal or unnoticeable.
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Verify TDCO with Scantool: Connect your OBD2 scantool and monitor the TDCO value. The scantool will display the learned TDCO value in degrees.
Adjusting TDCO Based on Scantool Readings
After performing the “KoKo” TDCO learn, if you find the TDCO value is outside the acceptable range, you may need to make minor adjustments to the injection pump.
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If TDCO is less than -0.5 degrees (more positive): This indicates the timing is too advanced (BTDC – Before Top Dead Center). Loosen the injection pump retaining nuts (except for one easily accessible nut to maintain position) and rotate the pump away from the turbo side to increase BTDC timing (make the TDCO value more negative).
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If TDCO is greater than -1.94 degrees (more negative): This indicates the timing is too retarded. Rotate the injection pump towards the turbo side to decrease BTDC timing (make the TDCO value more positive).
After each adjustment, tighten one nut to secure the pump and repeat the “KoKo” TDCO learn procedure and scantool verification until the TDCO value falls within the desired range of -1.54 degrees to -1.94 degrees. Aim for a value above -1.54 degrees for optimal performance.
Once you are close to the target range, you can use the scantool’s “TDCO LEARN” function for finer adjustments. Command TDCO LEARN with the scantool, and then slightly increase the engine idle speed until you observe the desired TDCO value. Immediately exit the TDCO LEARN function and re-verify the TDCO in the monitor-only screen.
Important Notes:
- DTCs and TDCO Learn: Ensure all DTCs are cleared before attempting TDCO adjustments, as timing adjustments will not function if DTCs are present.
- Idle Speed and DTCs: Avoid increasing the idle speed above approximately 1700 RPM during scantool TDCO LEARN, as this can trigger a TDCO DTC, requiring you to clear codes and restart the process.
- OBD2 Timing Readings: Ignore generic “TIMESET” or timing readings from OBD2. Focus solely on the TDCO value. A correct TDCO typically corresponds to a timing reading between +8.5 and +10 degrees, but this can vary based on ECT and IAT.
- Post-Adjustment Procedure: After achieving the correct TDCO and locking down the injection pump, take a final TDCO reading with your scantool for future reference. Drive the vehicle for several short trips (around 15 minutes each) with easy starts and stops to allow the PCM to relearn normal driving parameters with the new timing setting.
Final Considerations
The TDCO relearn procedure is a crucial step in ensuring your 6.5 diesel engine operates at its peak efficiency. Remember to perform the “KoKo” procedure no more than twice consecutively. If further adjustments are needed, drive the vehicle normally for about 15 minutes to allow the PCM to adapt to the new timing value before attempting the procedure again. In some cases, repeated TDCO LEARN attempts without allowing for PCM adaptation can lead to PCM non-cooperation.
By following these steps carefully, you can effectively perform a 6.5 OBD2 TDCO learn and optimize your diesel engine’s timing for improved performance and fuel economy. Always prioritize safety and consult a qualified mechanic if you are uncomfortable performing these procedures yourself.
