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Tools Required

J 35667-A Cylinder Leakdown Tester

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

  1. Remove the battery ground (negative) cable. Refer to


Before servicing any electrical component, the ignition key must be in the OFF or LOCK position and all electrical loads must be OFF, unless instructed otherwise in these procedures. If a tool or equipment could easily come in contact with a live exposed electrical terminal, also disconnect the negative battery cable. Failure to follow these precautions may cause personal injury and/or damage to the vehicle or its components.

in General Information.

  1. Remove the spark plugs. Refer to Ignition System.
  2. Install the J 35667-A .
  3. Measure each cylinder on the compression stroke, with both valves closed.


It may be necessary to hold the crankshaft balancer bolt, to prevent piston movement.

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


    • 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.
    • Inspect the four primary areas, to properly diagnose a leaking cylinder.
    • 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 the suspect cylinder head and inspect. 
    • If air is heard from the crankcase system at the crankcase (oil filler tube), perform the following procedure:
    • Remove the piston from the suspect cylinder.
    • Inspect the piston and connecting rod assembly.
    • Inspect the engine block.
    • If bubbles are found in the radiator, perform the following procedure:
    • Remove both cylinder heads and inspect. 
    • Inspect the engine block.
    • Remove the J 35667-A .
    • Install the spark plugs. Refer to Ignition System.
    • Install the battery ground (negative) cable. Refer to Battery.


    Bad Rings: air will blow through the oil filler when performing the leak-down.

    Bad Intake Valve: air will blow through the throttle body when performing the leak-down.

    Bad Exhaust Valve: air will blow through the tailpipe when performing the leak-down.

    September 01, 2019 — Joseph Losco