Ensuring optimal engine performance in your 6.5L diesel engine hinges on accurate timing, particularly the Top Dead Center Offset (TDCO). This guide details a step-by-step TDCO learn procedure using OBD2 diagnostic software and a scantool. Correct TDCO learning is crucial for engine efficiency and addressing timing and fuel delivery concerns. Follow these instructions for precise adjustment.
Before you begin, it is important to note: Do not attempt this procedure without a scantool. If your scantool provides a TDCO reading that differs from the result of this procedure, the value obtained from this procedure is the correct one relative to the actual position of the injection pump (IP).
If a timing adjustment is necessary, slightly loosen the injection pump, leaving the most accessible nut only partially loosened. This nut will secure the IP’s position both before and after any adjustment.
Here is the step-by-step procedure for performing a TDCO learn on a 6.5 diesel engine:
Step 1: Engine Warm-up and Initial Scan
Start by ensuring the engine is at its normal operating temperature. Using your scantool, clear all Diagnostic Trouble Codes (DTCs). Observe and record the initial TDCO value displayed by the scantool. This reading will serve as your baseline reference. Once recorded, turn off the engine.
Step 2: Accelerator Pedal and PCM Preparation
Turn the key to the “On” position (engine off). Fully depress the accelerator pedal and hold it down for at least 45 seconds. Then, release the pedal. This step allows the Powertrain Control Module (PCM) to prepare for the TDCO learn process.
Step 3: PCM Power Down
Turn the key to the “Off” position and leave it off for a minimum of 30 seconds. This allows the PCM to fully power down and clear its memory, including any learned driveability parameters. This memory reset is crucial for an accurate TDCO relearn.
Step 4: Engine Start and TDCO Relearn Initiation
Turn the key to the “On” position and start the engine. The TDCO relearn process will begin automatically 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 noise as the PCM searches for the correct injection position, especially if the timing is significantly off. If the timing is close to correct, these symptoms might be minimal or unnoticeable.
Step 5: Scantool Monitoring and TDCO Value Check
Connect your scantool and monitor the TDCO value in degrees. Note the reading.
Step 6: Injection Pump Adjustment (If Necessary)
Based on the TDCO reading from your scantool, adjust the injection pump accordingly. Remember that approximately 1mm of movement on the injection pump corresponds to about 2.5 degrees of timing change.
- If the TDCO value is less than -0.5 degrees (more positive), rotate the injection pump away from the turbo side to increase Before Top Dead Center (BTDC) timing.
- If the TDCO value is greater than -1.94 degrees (more negative), rotate the injection pump towards the turbo side to decrease BTDC timing.
After making a small adjustment, tighten one injection pump nut to secure its position.
Step 7: Repeat TDCO Learn Procedure
Repeat the “KoKo thing” (steps 2 through 5) to reassess the TDCO value after adjustment. Continue to repeat steps 6 and 7 as needed until the TDCO value is between -1.54 degrees and -1.94 degrees. Aim for a TDCO reading above -1.54 degrees within this range.
Step 8: Fine-tuning TDCO with Scantool (If Necessary)
Once the TDCO is within the -1.54deg to -1.94deg range, you can use your scantool to fine-tune the TDCO. Command the “TDCO LEARN” function in your scantool software. Slowly increase the idle speed until you observe the desired TDCO value. Once achieved, immediately exit the “TDCO LEARN” function and re-check the TDCO value in the monitor-only screen to confirm the adjustment.
Important Notes on TDCO Adjustment and RPM Limits:
- Exceeding approximately 1700 RPM during the scantool TDCO LEARN procedure can trigger a DTC. If this occurs, you must clear the DTCs before proceeding with any further timing adjustments. Timing adjustments will not function if any DTCs are present.
- Ignore OBD2 TIMESET or general timing readings. Focus solely on the TDCO value. If the TDCO is correctly set, the timing reading will typically be between +8.5 degrees and +10 degrees. This reading can vary slightly depending on Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT), especially in colder weather. A reading of +8.5 degrees indicates timing at the lower end of the acceptable range, while +10 degrees suggests timing at the higher end or that the PCM is still requesting more advance (check IAT to ensure it is not excessively high, above 85°F, which could falsely indicate advance demand).
Step 9: Finalizing and Securing the Injection Pump
Once the desired TDCO value is achieved and verified, fully tighten and secure all three injection pump nuts to the specified torque.
Step 10: Final TDCO Reading and PCM Relearn Drive Cycles
Take a final TDCO reading with your scantool for future reference and record it. It is crucial to perform several easy start-off and driving cycles, each lasting about 15 minutes. This allows the PCM to relearn normal driveability parameters based on the new TDCO setting.
Important Note on Relearn Persistence and Procedure Limits:
- The TDCO relearn is permanent. It will not change during normal vehicle operation. To alter the TDCO value, you must repeat either this “KoKo” procedure or use the scantool’s TDCO LEARN function.
- Do not perform this procedure more than twice consecutively. If repeated attempts are made without driving, the PCM may become unresponsive to further TDCO LEARN attempts. Drive the vehicle normally for approximately 15 minutes after two attempts to allow the PCM to adjust driveability parameters to the new timing value before attempting the procedure again. Some reports suggest the PCM may become uncooperative if TDCO LEARN is attempted too frequently in a short period without allowing time for other operational parameters to relearn.
By following these steps carefully, you can effectively perform a TDCO learn procedure on your 6.5 diesel engine using OBD2 software, ensuring optimal engine timing and performance.
