With the use of air pressure, a leak test will aid in diagnosing cylinder leakage. If necessary, the leak test may be used in conjunction with the engine compression test, in order to help isolate the cause of leaking cylinders.

Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

1. Remove the negative battery cable.
2. Remove the spark plug. Refer to Ignition System.
3. Install J 35667-A Cylinder Leakdown Tester.
4. Measure the cylinder on the compression stroke, with both valves closed.

Important: It may be necessary to hold the crankshaft balancer bolt/screw, in order to prevent piston movement.

5. Apply air pressure, using J 35667-A . Refer to the manufacturer's instructions.
6. Repeat the leak test for each cylinder.
7. Record the leakage readings for all of the cylinders.

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.

8. Inspect the 4 primary areas, in order to properly diagnose a leaking cylinder.
9. If escaping air is heard from the intake system at the throttle body, perform the following procedure:

•	Remove the rocker cover on the suspect cylinder. Refer to Valve Rocker Arm Cover Replacement .

•	Ensure that both valves are closed.

•	Inspect the cylinder head for a broken valve spring. Refer to Valve Train Components Cleaning and Inspection .

•	Inspect the cylinder head for a burnt valve face or valve seat. Refer to Valve Train Components Cleaning and Inspection .

10. If escaping air can be heard from the exhaust system at the tailpipe, perform the following procedure:

•	Remove the rocker cover on the suspect cylinder. Refer to Valve Rocker Arm Cover Replacement .

•	Ensure that bolt valves are closed.

•	Inspect the cylinder head for a broken valve spring. Refer to Valve Train Components Cleaning and Inspection .

•	Inspect the cylinder head for a burnt valve face or valve seat. Refer to Valve Train Components Cleaning and Inspection .

11. If escaping air is heard from the crankcase system at the crankcase (oil filler tube), perform the following procedure:

•	Remove the piston from the suspect cylinder. Refer to Connecting Rod, Bearing and Piston Replacement .

•	Inspect the crankcase system for missing or damaged piston rings. Refer to Piston and Connecting Rod Inspection .

•	Inspect the cylinder bore diameter and finish. Refer to Engine Block Cleaning and Inspection .

12. If escaping air is causing bubbles in the cooling system radiator, perform the following procedure:

•	Remove both cylinder heads and inspect for damaged cylinder head gaskets. Refer to Cylinder Head Replacement .

•	Inspect the cylinder block. Refer to Engine Block Cleaning and Inspection .

•	Inspect the cylinder heads. Refer to Cylinder Head Cleaning and Inspection .

13. Remove J 35667-A .
14. Install the spark plug. Refer to Ignition System.
15. Install the negative battery cable.