Logging your B8 S4 with VCDS (formerly VAGCOM) is crucial for understanding your car’s performance, especially if it’s tuned. This guide provides a step-by-step walkthrough of how to log your Audi S4 using a Ross-Tech VCDS cable and software, focusing on essential performance parameters. We’ll cover setup, logging procedures, and interpreting the results.
Preparing for your VCDS Log
Before diving into logging, ensure you have the necessary equipment: a Ross-Tech VCDS cable and compatible Windows software. While different VCDS versions may have slight variations in parameter location numbers, the process remains largely consistent. Remember, logging with VCDS requires Windows software.
Step 1: Connect and Launch: Connect the VCDS cable to your car’s OBDII port, located under the dash on the driver’s side. Turn your car on and launch the VCDS software.
Step 2: Fault Code Check: Begin by scanning for fault codes. In VCDS, click “Auto-Scan,” then “Start.” Address any existing faults before proceeding. Save the scan results and clear faults using the “Clear all DTC’s” button.
Setting Up VCDS for Logging Your B8 S4
Step 3: Select Engine Module: From the main menu, click “Select” under “Select Control Module,” then choose “01-Engine” under the “Common” tab.
Step 4: Access Advanced Measurement Values: In the Engine Controller module, click “Adv. Meas. Values” to enter the logging section.
Step 5: Record Ambient Air Pressure: Find and select “Ambient Air Pressure.” Note the displayed value for later boost calculations, then uncheck the box.
Step 6: Selecting Key Logging Parameters: Choose the parameters you want to monitor. For a comprehensive performance log, consider these:
- 002: Accelerator Position (%)
- 009: Charge Air Pressure Specified Value (hPa)
- 018: Engine Speed (RPM)
- 089: Air Mass (kg/h)
- 186: Ignition Angle; Actual (degrees)
- 188: Intake Air Temperature (degrees C)
- 190: Intake Manifold Pressure; Absolute (hPa)
- 418-423: IGA_AD_KNK[0-5] (degrees) – Select two cylinders for knock detection monitoring.
- 540: RFP_AV (Bypass Valve Percentage)
Step 7: Saving Your Parameter Selection for future Vcds Log B8 S4: Save this parameter list for easy access later. Click the VCDS icon (top-left corner), name it “Performance,” or something descriptive.
Performing the VCDS Log on Your B8 S4
Step 8: Optimizing Logging Speed: This is crucial. Click the “Turbo” button and check “Group UDS requests.” This significantly improves logging resolution by aligning timestamps.
Step 9: Initiating and Starting the Log: Click “Log,” then “Start” to begin recording data. Your car should be running.
Step 10: Conducting the Logging Run: Perform a full 3rd (or 4th) gear pull, ideally from 3000 to 7000 RPM. Ensure consistent conditions:
- Controlled environment (drag strip or dyno preferred)
- A/C and radio off
- Windows up
- Dynamic mode enabled (if available)
- Traction/ASR off
Step 11: Stopping and Saving: Once the run is complete, click “Stop” then “Done, close.” The log file (.CSV format) will be saved in the Ross-Tech/VCDS/Logs folder.
Interpreting Your B8 S4 VCDS Log Results
Analyzing the logged data helps assess your S4’s performance. Here’s a breakdown of key parameters:
- Boost: Calculate requested and actual boost using logged values and ambient air pressure. Compare them to identify potential issues like leaks or insufficient boost. Stock S4s typically peak around 10-11 PSI, while tuned cars can reach higher pressures.
- Air Mass: Higher values indicate better airflow, potentially correlating with increased power.
- Intake Air Temperature: Lower temperatures are desirable for optimal performance. High IATs can lead to reduced timing and power.
- Ignition Timing: Look for timing pull (negative values in IGA_AD_KNK) which signifies knock. Excessive knock indicates potential problems with fuel quality, engine health, or tune.
- Bypass Valve: Ideally, the bypass valve should remain closed (0%) during a pull. Opening indicates boost exceeding the requested pressure or potential issues with the diverter valve.
By understanding how to perform and interpret a vcds log b8 s4, you can gain valuable insights into your car’s performance and identify areas for improvement or potential problems. This data is particularly useful when diagnosing issues or fine-tuning performance modifications. Remember to log consistently under similar conditions for accurate comparisons.
