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Compression Test .
Faulty external engine
oil cooler
Faulty cylinder head
gasket
Warped cylinder head Machine the cylinder head to proper flatness, if applicable, and replace the
Cracked cylinder head Replace the cylinder head and gasket.
Cracked cylinder liner
or engine block
Cylinder head, block,
or manifold porosity
ENGINE COMPRESSION TEST
1. Charge the battery if the battery is not fully charged.
2. Disable the ignition system.
3. Disable the fuel injection system.
4. Remove all the spark plugs.
5. Turn the ignition to the ON position.
6. Depress the accelerator pedal to position the throttle plate wide open.
7. Start with the compression gauge at zero and crank the engine through four compression strokes, 4 puffs.
8. Check the compression for each cylinder. Record the readings.
9. If a cylinder has low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the
combustion chamber through the spark plug hole. Recheck the compression and record the reading.
10. The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder.
No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any one
cylinder is 1 035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa
(105 psi). (1 035 x 70% = 725) (150 x 70% = 105).
Normal - Compression builds up quickly and evenly to the specified compression for each cylinder.
Piston Rings Leaking - Compression is low on the first stroke. Then compression builds up with the
following strokes but does not reach normal. Compression improves considerably when you add
oil.
Valves Leaking - Compression is low on the first stroke. Compression usually does not build up on
the following strokes. Compression does not improve much when you add oil.
If 2 adjacent cylinders have lower than normal compression, and injecting oil into the cylinders
does not increase the compression, the cause may be a head gasket leaking between the cylinders.
ENGINE BALANCING
The 1997-2004 5.7L LS1/LS6 engine with crankshaft balancer is a balanced assembly. On manual transmission
Replace the components as required.
Replace the head gasket and components as required. Refer to Cylinder Head
Cleaning and Inspection , Cylinder Head Replacement - Left and Cylinder
Head Replacement - Right .
cylinder head gasket. Refer to Cylinder Head Cleaning and Inspection .
Replace the components as required.
Replace the components as required.
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