Hummer H3. Instruction - page 83

Fig. 24: Measuring Engine Compression
Courtesy of GENERAL MOTORS CORP.

5. Measure the engine compression, using the following procedure:

1. Firmly install J 38722 to the spark plug hole. See Special Tools.

2. Have an assistant crank the engine through at least four compression strokes in the

testing cylinder.

3. Check and record the readings on J 38722 at each stroke. See Special Tools.

4. Disconnect J 38722 . See Special Tools.

5. Repeat the compression test for each cylinder.

6. Record the compression readings from all of the cylinders. A normal reading should be

approximately 1482 kPa (215 psi).

2006 Hummer H3

2006 ENGINE Engine Mechanical - 3.5L (L52) - H3

The lowest reading should not be less than 70 percent of the highest reading.

7. The following are examples of the possible measurements:

When the compression measurement is normal, the compression builds up quickly and
evenly to the specified compression on each cylinder.

When the compression is low on the first stroke and tends to build up on the following
strokes, but does not reach the normal compression, or if the compression improves
considerably with the addition of three squirts of oil, the piston rings may be the cause.

When the compression is low on the first stroke and does not build up in the following
strokes, or the addition of oil does not affect the compression, the valves may be the
cause.

When the compression is low on two adjacent cylinders, or coolant is present in the
crankcase, the head gasket may be the cause.

8. Install the air duct to the throttle body.

9. Install the spark plugs.

10. Enable the fuel system.

11. Install the ignition control modules.

CYLINDER LEAKAGE TEST

Tools Required

J 35667-A Cylinder Head Leakdown Tester. See Special Tools.

2006 Hummer H3

2006 ENGINE Engine Mechanical - 3.5L (L52) - H3

Fig. 25: Checking For Cylinder Leakage
Courtesy of GENERAL MOTORS CORP.

CAUTION: Refer to Battery Disconnect Caution in Cautions and

Notices.

2006 Hummer H3

2006 ENGINE Engine Mechanical - 3.5L (L52) - H3

1. Disconnect the battery ground negative cable.

2. Remove the spark plugs. Refer to Spark Plug Replacement in Engine Control.

3. Rotate the crankshaft to place the piston in the cylinder being tested at Top Dead Center

(TDC) of the compression stroke.

4. Install J 35667-A . See Special Tools.

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

instructions. See Special Tools.

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 control module or air inlet hose may indicate a worn
or burnt intake valve or a broken valve spring.

Air leakage sounds at the exhaust system tailpipe 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 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

IMPORTANT: A leakage test may be performed to measure

cylinder/combustion chamber leakage. High cylinder leakage
may indicate one or more of the following:

Worn or burnt valves

Broken valve springs

Stuck valve lash adjuster

Damaged piston

Worn piston rings

Worn or scored cylinder bore

Damaged cylinder head gasket

Cracked or damaged cylinder head

Cracked or damaged engine block

IMPORTANT: It may be necessary to hold the crankshaft balancer bolt to

prevent the engine from rotating.

2006 Hummer H3

2006 ENGINE Engine Mechanical - 3.5L (L52) - H3

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