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Home >> Buick >> 2021 >> Envision Preferred, AWD >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls And Fuel - 2.0L (LSY) - Diagnostic Information And Procedures (2 Of 2) >> Diagnostic Information and Procedures >> Relative Engine Compression Test >> Circuit/System Testing
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Circuit/System Testing

  1. Ignition/Vehicle - Off
  2. Apply - Parking Brake
  3. Install - CH-51450-A Oscilloscope Diagnostic Kit & CH-51450-LEAD-A Oscilloscope Basic Lead Kit
    1. Channel A Lead: Blue @ Oscilloscope
    2. Channel A Lead: Blue @ B+ & Ground
    4. NOTE:

    Hover the mouse cursor over an icon button to display the button's description.

  5. Coupling - DC
  6. Select: Connect Detect

    Verify the following information is correctly displayed: Connected Channels = Green

    • If the information is not correctly displayed 

      Repair the poor connection & Repeat this step

    • Go to next step: If the information is correctly displayed 
  7. Setup - CH-51450-A Oscilloscope Diagnostic Kit & CH-51450-LEAD-A Oscilloscope Basic Lead Kit
    1. Select: Automotive
    2. Select: Charging and Starting
    3. Select: Relative Compression
    4. Select: Voltage
  8. Select: Start Capturing
  9. Perform the following action:
      NOTE:

      Make sure the component is not obstructed: Accelerator Pedal

    1. Fully Applied - Accelerator Pedal - Wide Open Throttle
    2. {Automatic Transmission} Apply & Hold - Brake Pedal

      {Manual Transmission} Apply & Hold - Clutch Pedal

    3. Engine - Cranking - For 5 - 10 s
    4. Select: Stop Capturing

      Verify the following information is correctly displayed: The waveform valleys are all even. Refer to: Oscilloscope Waveform Library

    • If the information is not correctly displayed 

      Verify the condition does not exist with the component and repair as necessary:

      NOTE:

      The following are examples of what could cause compression issues. Inspect all mechanical components for the applicable cylinder. The list is not all encompassing refer to: Symptoms - Engine Mechanical

    • Camshaft Lobe(s) - Visible Damage/Worn
    • Exhaust Valve or Intake Valve - Stuck Open/Visible Damage
    • Exhaust Valve Seat or Intake Valve Seat - Visible Damage
    • Piston - Cracked/Visible Damage
    • Piston Ring - Seized/Visible Damage/Worn
    • Valve Lifter - Visible Damage/Worn
    • Valve Spring - Visible Damage/Worn
    • Valve Rocker Arm - Visible Damage/Worn
    • Go to next step: If the information is correctly displayed 
  10. All OK.
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