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Cylinder Leakage Test

Cylinder Leakage Test


Special Tools

EN-35667-A Cylinder Head Leakdown Tester

For equivalent regional tools, refer to Special Tools (LDK, LHU) .


Note

A leakage test may be performed in order to measure cylinder/combustion chamber leakage. High leakage may indicate one or more of the following conditions:



• Worn or burnt valves

• Broken valve springs

• Stuck valve lifters

• Incorrect valve lash/adjustment

• Damaged piston

• Worn piston rings

• Worn or scored cylinder bore

• Damaged cylinder head gasket

• Cracked or damaged cylinder head

• Cracked or damaged engine block



1.
Warning

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.

For Vehicles equipped with OnStar® (UE1) with Back Up Battery:

The Back Up Battery is a redundant power supply to allow limited OnStar® functionality in the event of a main vehicle battery power disruption to the VCIM (OnStar®module). Do not disconnect the main vehicle battery or remove the OnStar® fuse with the ignition key in any position other than OFF. Retained accessory power (RAP) should be allowed to time out or be disabled (simply opening the driver door should disable RAP) before disconnecting power. Disconnecting power to the OnStar® module in any way while the ignition is On or with RAP activated may cause activation of the OnStar® Back-Up Battery (BUB) system and will discharge and permanently damage the back-up battery. Once the Back-Up Battery is activated it will stay on until it has completely discharged. The BUB is not rechargeable and once activated the BUB must be replaced.


Disconnect the battery ground negative cable.

2. Remove all spark plugs. Refer to Spark Plug Replacement .

3. Rotate the crankshaft to place the piston in the cylinder being tested at top dead center (TDC) of the compression stroke.

4. Install the EN-35667-A Tester or equivalent.

5.
Note

It may be necessary to hold the crankshaft balancer bolt to prevent the engine from rotating.


Apply shop air pressure to the EN-35667-A Tester and adjust according to the manufacturers instructions.

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:

• Air leakage sounds at the throttle body or air inlet hose that may indicate a worn or burnt intake valve or a broken valve spring.

• Air leakage sounds at the exhaust system tailpipe that may indicate a worn or burnt exhaust valve or a broken valve spring.

• Air leakage sounds from the crankcase, oil level indicator tube, or oil fill tube that may indicate worn piston rings, a damaged piston, a worn or scored cylinder bore, a damaged engine block or a damaged cylinder head.

• Air bubbles in the cooling system may indicate a damaged cylinder head or a damaged cylinder head gasket.

7. Perform the leakage test on the remaining cylinders and record the values.