Chevrolet Silverado / GMC Sierra. Service manual — part 406

for the cylinder being tested.

10. Observe the J 26999 and note the reading as the compression test is being performed. See

Special Tools. A normal cylinder reading will be indicated if compression builds up
quickly and evenly to the specified level. An abnormal reading will be indicated if
compression is low on the first compression stroke, starts increasing on the following
compression strokes but does not reach the specified level.

11. Record the compression reading for the cylinder just tested.

12. Disconnect the J 26999 from the EN-47603 and remove adapter from the glow plug hole.

See Special Tools.

13. Repeat steps 8 through 13 for all remaining cylinders. All 8 cylinders must be tested to

obtain valid test results. Record the readings.

14. The minimum compression in any one cylinder is 2069 kPa (300 psi). There should not be

more than 345 kPa (50 psi) difference between a suspect cylinder and the average
compression of all 8 cylinders.

Normal-Compression builds up quickly and evenly to the specified compression for
each cylinder.

Piston Rings Leaking-Compression is low on the first stroke. Compression builds up
with the following strokes but does not reach normal.

Valves Leaking-Compression is low on the first stroke. Compression usually does not
build up on the following strokes.

CYLINDER LEAKAGE TEST

Tools Required

J 35667-A Cylinder Head Leakdown Tester

J-35667-8 Cylinder Head Leakdown Adapter. See Special Tools.

Test

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Fig. 45: Testing Cylinder Leakage
Courtesy of GENERAL MOTORS CORP.

CAUTION: Refer to BATTERY DISCONNECT CAUTION

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, burnt, or stuck valves

Broken valve springs

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

1. Disconnect the battery ground negative cable.

2. Remove the glow plugs.

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-35667-8 and J 35667-A . See Special Tools.

5. Apply shop air pressure to J 35667-A 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 intake manifold tube, may indicate a worn, stuck or burnt
intake valve, broken valve spring, incorrect valve lash or damaged valve train
components.

Air leakage sounds at the exhaust system tailpipe may indicate a worn, burnt, or stuck
exhaust valve, broken valve spring, incorrect valve lash or damaged valve train
components.

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 gasket.

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

OIL CONSUMPTION DIAGNOSIS

Incorrect valve lash

Damaged valve train components

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.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

The accepted rate of oil consumption, not due to leaks, is the use of 0.946 liter (1 qt) or less
within 379 liters (100 gallons) of fuel used. This rate only applies to vehicles under warranty,
maintained in accordance with the appropriate maintenance schedule, driven at legal speeds and
within design intent of the vehicle.

Oil economy should not be tested until the vehicle has accumulated at least 8000 km (5000 mi)
and the oil has been changed for the first time. During initial engine break-in periods before the
first oil change, oil consumption may exceed 1.9 liters (2 qts) or more per 379 liters (100 gallons)
of fuel used.

Checks

Causes

Preliminary

The causes of excessive oil consumption may include the
following conditions:

External oil leaks

Refer to Oil Leak Diagnosis.

Incorrect oil level or improper reading of the oil level
indicator

With the vehicle on a level surface, run the engine for a
few minutes, allow adequate drain down time (2-3
minutes) and check for the correct engine oil level.

Improper oil viscosity

Refer to the vehicle owners manual and use the
recommended SAE grade and viscosity for the prevailing
temperatures.

Continuous high speed driving and/or severe usage

Crankcase ventilation system restrictions or
malfunctioning components

Oil residue in the charge air cooler system is normal with
a closed PCV system

Worn valve guides and/or valve stems

Worn or improperly installed valve stem oil seals

Piston rings broken, worn, not seated properly

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado