A boost leak can hinder the car's performance and potentially cause long-term damage to the engine. That's why boost leak testing is crucial for maintaining the optimal performance of your vehicle. When your vehicle is being tuned, your calibrator (tuner) may suggest you have a boost leak that needs to be resolved before proceeding with tuning.

    What is a boost leak?

    Before we dive into boost leak testing, let's understand what a boost leak is. In a turbocharged engine, the boost system delivers pressurized air from the turbocharger to the engine's intake manifold. This pressurized air, commonly referred to as boost, enhances the engine's power output.

    A boost leak occurs when there is an unintended loss of boost pressure due to a faulty or compromised component within the boost system. Common culprits of boost leaks include damaged intercooler hoses, loose or cracked connections, faulty clamps, defective diverter valve, defective PCV system, faulty SAI (secondary air injection on NAR Golf GTI/Audi A3/Jetta GLI) or a deteriorated intercooler. When a boost leak is present, the engine may not receive the intended amount of boost pressure resulting in decreased performance, slower acceleration, and potential damage to engine components.


    A typical datalog screenshot depicting a potential boost leak

    • Relative Manifold Pressure (psi) – MAP sensor located on Intake Manifold.
    • Boost Press. (psi) – PUT sensor located in throttle pipe.
    • Trgt. Boost Press. (psi) – Commanded boost pressure target.
    • Turbine Act. Base Value (%) – Commanded wastegate position in percentage.
    • Turbine Act. Final Value (%) – Actual wastegate position in percentage.

    In the screenshot snippet above, you can clearly see that the wastegate is closed in some points 40% greater than the commanded duty cycle, all while not being able to achieve the Trgt. Boost Press. (psi) target. This is most often the result of a system boost leak where the pressure is escaping, and the turbocharger is working much harder to try and reach/maintain the Trgt. Boost Press. (psi) value.

     Why is boost leak testing important?

     Boost leak testing is an essential preventive maintenance procedure that helps ensure your vehicle is performing at its best. By identifying and rectifying any boost leaks, you can prevent potential issues such as reduced power, decreased fuel efficiency, engine misfires, and even long-term damage to vital engine components.

     Boost leak testing not only helps maintain optimal performance but also safeguards the longevity of your vehicle. By addressing boost leaks early on, you can prevent further damage to the engine, turbocharger, and associated components, thereby potentially saving you from costly repairs in the future.

     How to perform boost leak testing?

     Performing boost leak testing on the EA888.3 involves a systematic approach to identify potential leaks and pinpoint their locations. Here's a step-by-step guide to help you conduct a thorough boost leak test:

    1.  Preparation: Ensure your vehicle is parked on a flat surface, the engine is cool, and the ignition is off. Gather the necessary tools, including a boost leak tester, a set of adapters specific to your vehicle, a flashlight, and a wrench or socket set.



    CTA Manufacturing 7912 Boost Leak Detection Kit

    1. Locate the boost system components: Familiarize yourself with the various components of the boost system, such as intercooler hoses, clamps, connections, PUT and MAP sensor locations, Diverter Valve, Wastegate Actuator, and SAI valve (if so equipped; GTi/A3).


    1.Turbo Charge Pipe
    5. Charge Pipe coupler
    7. Intercooler
    15. PUT Sensor
    16. PUT Sensor Gasket
    17. Throttle Pipe Coupler
    18. Throttle Pipe

       Intercooler and Charge/Throttle piping

      5. Wastegate Actuator
      8. Turbo Muffler
      9. Turbo Muffler Gasket
      11. Diverter Valve
      12. Diverter Valve Gasket
      13. Turbo

        Turbocharger component view

      14. Intake Manifold Gasket
      15. Intake Manifold
      18. Intake MAP Sensor
      19. Throttle Control Valve

      Intake Manifold component view with Direct Injection


      1. Connect the boost leak tester: The most commonly used tester for stock-style turbochargers is the APR boost pressure tester, shown below. These products are discontinued but shown as example:

        APR’s Boost Leak Tester Adapter for stock turbochargers, Discontinued.

        APR Boost Leak Tester Regulator, Discontinued.


        This tester requires you to remove your intake from your turbocharger, which also disconnects the Positive Crankcase Ventilation hose from the system. This is an efficient method for testing the entire system and prevents damage to the PCV system as it is not designed to see charged pressure. It is recommended that your air supply has a ball valve easily accessible so that you can shut off the air supply, or vary the pressure to the system. (Pic below)


        Typical ball valve for air supply.


        Alternatively, you can use a test kit similar to the CTA posted above, connected to an intake elbow. You must ensure that to protect the PCV system, you disconnect the PCV elbow from the intake and cap the port of the intake elbow sufficiently. ECS manufactures a convenient PCV elbow cap, however using a dust cap of appropriate size and a zip tie will also work. 


        Left: PCV Elbow on intake inlet shown from AToM V2. Intake. Right: ECS PCV Cap

        1. Pressurize the system: Using a regulator, set the line pressure to the recommended pressure:
          • Stock turbo: 30psi
          • Vortex or similar hybrid: 40psi
          • Typhoon or similar (large frame): 50psi

        Slowly start to introduce pressure into the system, listening for obvious leaks. Some leaks do not always present immediately. We recommend the above static pressures as they are at or above target pressures depending on your setup.


        1. Inspect for leaks: With the boost system pressurized, systematically inspect all the components, connections, and hoses for signs of leaks. Pay close attention to areas prone to leaks, such as hose joints, intercooler connections, and any visible cracks or damages. Use a combination of visual inspection, listening for hissing sounds, and feeling for air leaks around connections and hoses. To aid in leak detection, you can use a spray bottle with a tiny amount of dish soap. Spray around the above mentioned areas and the soapy water will provide you a quickly observable leak if one is present. A small amount of air leakage is expected as not all intake and exhaust valves are closed at any point, but any significant or audible leaks should be identified and addressed. NOTE: Testing methods cannot accurately determine if the diverter valve located on the compressor cover is leaking internally, only if the seal is damaged/torn will you hear/feel air escape.


        1. Road test to obtain new datalogs: After you have sufficiently repaired any leaks, retest and obtain datalogs for your calibrator.


        NOTE: If you have successfully tested your system and find no leaks externally, there still may be leaks present such as the diverter valve, or PCV plate. These components cannot be easily tested with standard procedures and may require replacement if testing reveals no leaking.