Tools Required

J 35667-A  Cylinder Head 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.
2. Remove the spark plugs. Refer to SPARK PLUGS in Engine Performance - Removal and Installation.
3. Install the J 35667-A  .
   Fig 1: Measuring Each Cylinder On Compression Stroke

   Courtesy of GENERAL MOTORS CORP.
4. Measure each cylinder on the compression stroke, with both valves closed.

   Important:  It may be necessary to hold the crankshaft balancer bolt, 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 12-18 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 four primary areas, 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 the suspect cylinder head and inspect. 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:
   • Remove the piston from the suspect cylinder.
   • Inspect the piston and connecting rod assembly. Refer to PISTON, CONNECTING ROD, AND BEARINGS CLEANING AND INSPECTION  .
   • Inspect the engine block. Refer to ENGINE BLOCK CLEANING AND INSPECTION  .
10. If bubbles are found in the radiator, perform the following procedure:
    • Remove both cylinder heads and inspect. Refer to CYLINDER HEAD CLEANING AND INSPECTION  .
    • Inspect the engine block. Refer to ENGINE BLOCK CLEANING AND INSPECTION  .
11. Remove the J 35667-A  .
12. Install the spark plugs. Refer to SPARK PLUGS in Engine Performance - Removal and Installation.
13. Install the battery ground - negative cable.