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Testing Procedure

WARNING: This page is about a different car, the 2003 Pontiac Montana, 2003 Oldsmobile Silhouette, and 2003 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.

Tools Required 

J 35667-A  Cylinder Head Leakdown Tester

With the use of air pressure, a cylinder leakage test will aid in the diagnosis. Use the cylinder leakage test in conjunction with the engine compression test in order to isolate the cause of leaking cylinders.

CAUTION: Refer to BATTERY DISCONNECT CAUTION in Cautions and Notices.
  1. Disconnect the negative battery cable.
  2. Remove the spark plugs. Refer to ENGINE CONTROLS - REMOVAL & INSTALLATION & OVERHAUL  in Removal and Installation in Engine Performance.
  3. Install the J 35667-A. 
  4. Measure each cylinder on the compression stroke, with both valves closed.

    Important:  Hold the crankshaft balancer bolt in order to prevent piston movement.

  5. Apply air pressure, using the J 35667-A.  Refer to the manufacturer's instructions.
  6. Record the cylinder leakage readings for each cylinder.

    Important: 

    • Normal cylinder leakage is from 12 to 18 percent.
    • Make a note of any cylinder with more leakage than the other cylinders.
    • Any cylinder with 30 percent leakage or more requires service.
  7. Inspect the 4 primary areas in order to properly diagnose a leaking cylinder.
  8. If air is heard from the intake or exhaust system, perform the following procedure:
    • Remove the valve rocker arm cover of the suspect cylinder head.
      • Ensure that both valves are closed.
      • Inspect the cylinder head for a broken valve spring.
    • Remove and inspect the suspect cylinder head. Refer to CYLINDER HEAD CLEANING AND INSPECTION   . 
  9. If air is heard from the crankcase system at the crankcase oil filler tube, perform the following procedure:
    1. 9.1 Remove the piston from the suspect cylinder.
    2. 9.2 Inspect the piston and connecting rod assembly. Refer to PISTON, CONNECTING ROD, AND BEARINGS CLEANING AND INSPECTION   . 
    3. 9.3 Inspect the engine block. Refer to ENGINE BLOCK CLEANING AND INSPECTION   . 
  10. If bubbles are found in the radiator, perform the following procedure:
  11. Remove the J 35667-A. 
  12. Install the spark plugs. Refer to ENGINE CONTROLS - REMOVAL & INSTALLATION & OVERHAUL  in Removal and Installation in Engine Performance.
  13. Connect the negative battery cable. Refer to BATTERY DISCONNECT CAUTION in Cautions and Notices.
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