GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 Sierra - 2WD 🢒 Engine 🢒 Engine Mechanical - 4.3L 🢒 Cylinder Leakage Test

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 the Preface section.

  1. Disconnect the battery ground negative cable.
  2. Remove the spark plugs. Refer to Spark Plug Replacement use for the 4.3L engine.
  3. Rotate the crankshaft to place the piston in the cylinder being tested at top dead center (TDC) of the compression stroke, with both valves closed.
  4. Install the J 35667-A .

    5. Important: It may be necessary to hold the crankshaft balancer bolt to prevent piston movement.

  5. Apply shop air pressure to the J 35667-A and adjust according to the manufacturer instructions.

    6. Important: Perform the leakage test on all cylinders and record the values before doing any repairs.

  6. Record the cylinder leakage value. Cylinder leakage that exceeds 25 percent is considered excessive and may require component service. In excessive leakage situations, inspect for the following conditions:
    7. 6.1. Air leakage from the intake or exhaust system may indicate a worn or burnt valve or a broken valve spring.
             6.1.1. Remove the valve rocker arm cover of the suspect cylinder head. Refer to Valve Rocker Arm Cover Replacement - Left Side or Valve Rocker Arm Cover Replacement - Right Side .

             6.1.2. Ensure that both valves are closed.
             6.1.3. Inspect the cylinder head for a broken valve spring.
             6.1.4. Remove and inspect the suspect cylinder head. Refer to Cylinder Head Replacement - Left Side or Cylinder Head Replacement - Right Side .
    6.2. Air leakage from the crankcase, oil level indicator, or oil fill tube may indicate worn piston rings, a damaged piston, a worn or scored cylinder bore, a damaged engine block or a damaged cylinder head.
             6.2.1. Remove the piston from the suspect cylinder. Refer to Piston, Connecting Rod, and Bearing Removal or Piston, Connecting Rod, and Bearing Installation .
             6.2.2. Inspect the piston and connecting rod assembly. Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection .
             6.2.3. Inspect the engine block. Refer to Engine Block Cleaning and Inspection .
             6.2.4. Inspect the cylinder head. Refer to Cylinder Head Cleaning and Inspection .
    6.3. Air bubbles in the cooling system may indicate a damaged cylinder head or a damaged cylinder head gasket.
             6.3.1. Remove both cylinder heads. Refer to Cylinder Head Replacement - Left Side or Cylinder Head Replacement - Right Side .
             6.3.2. Inspect both cylinder heads. Refer to Cylinder Head Cleaning and Inspection .
             6.3.3. Inspect the engine block. Refer to Engine Block Cleaning and Inspection .
  7. Remove the J 35667-A .
  8. Install the spark plugs. Refer to Spark Plug Replacement use for the 4.3L engine.

    9. Caution: Refer to Battery Disconnect Caution in the Preface section.

  9. Connect the battery ground negative cable.