Boost pressure is a critical parameter for turbocharged engines like Volkswagen’s TSI and TDI. Monitoring and understanding boost readings using VCDS (Vag-Com Diagnostic System) is essential for diagnosing performance issues. This article explains how to use specific VCDS blocks to analyze requested versus actual boost in both gasoline TSI and diesel TDI engines.
Locating Boost Data with VCDS Blocks
Boost data resides in different Measuring Block Groups (Mbar Vcds Block) depending on the engine type. For TSI engines, boost pressure is typically found in Group 115. However, always consult your vehicle’s specific Ross-Tech VCDS label file for the correct group number. For TDI engines, boost pressure readings are usually located in Group 11.
Essential Supporting Data
Analyzing boost in isolation can be misleading. To get a comprehensive picture, it’s crucial to log additional data alongside boost pressure.
For TDI engines, simultaneously logging Group 03 (MAF and EGR values) or Group 10 (MAF and gas pedal position) provides valuable context. This helps determine if issues with airflow or EGR operation are affecting boost performance.
In TSI engines, logging a group indicating throttle valve angle or gas pedal position, such as Group 117, is recommended. If the engine is equipped with an EGR valve, logging Group 76 for EGR data is also beneficial.
Effective Logging Procedure for Accurate Boost Analysis
To accurately compare requested and actual boost, a specific driving cycle is necessary. Find a safe, open road and perform the following steps:
- Gear and RPM: Engage 3rd gear and maintain a steady RPM of around 1000-1500.
- Initiate Logging: Begin logging the selected boost group and its corresponding supporting data group. Limit logging to two groups per log to avoid data overload.
- Full Throttle Acceleration: Floor the gas pedal and maintain it until the engine reaches 4000-5000 RPM (adjust the upper limit based on engine type and safety). The critical data lies within the 2000-4000 RPM range where boost builds steadily.
- Data Analysis: Plot the logged data with requested and actual boost on the Y-axis and RPM on the X-axis. Include MAF and EGR data on the same plot for correlation. This visual representation allows for easy comparison and identification of discrepancies between requested and actual boost.
Interpreting Boost Discrepancies: TSI vs. TDI
Differences between requested and actual boost can arise due to various factors. In TSI engines, the MAP (Manifold Absolute Pressure) sensor is located before the throttle body. This means that at partial throttle, the MAP sensor reading might not accurately reflect the actual boost pressure in the intake manifold.
TDI engines lack a throttle body, so the MAP sensor more closely tracks intake pressure, resulting in a closer correlation between requested and actual boost even at partial load.
However, for accurate boost testing in both TSI and TDI engines, measurements should always be taken under full load conditions with the throttle wide open. Plotting data against RPM provides a clearer picture of boost performance across the engine’s operating range.
Conclusion
Analyzing “mbar vcds block” data for boost pressure is a powerful diagnostic technique for TSI and TDI engines. By following the outlined procedures and understanding the nuances of each engine type, you can effectively identify and troubleshoot boost-related performance issues. Remember to always consult the Ross-Tech VCDS label file for your specific vehicle to ensure you are using the correct measuring block groups.
