Chevrolet Silverado / GMC Sierra. Service manual — part 11

on the following strokes, and does not reach normal. Compression does not improve
much, if at all, when you add oil.

Head gasket leaking

Compression is low on the first stroke. The compression does not build up on the
following strokes, and does not reach normal. Compression does not improve much, if
at all, when you add oil. Adjacent cylinders have the same, or similar, low
compression readings.

15. If one or more cylinders fails to meet the minimum specified compression, repair or replace

all damaged or worn components and test the engine again.

CYLINDER LEAKAGE TEST

Tools Required

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

Test

With the use of air pressure, a cylinder leakage test will aid in the diagnosis. Use the cylinder
leakage test in conjunction with the engine compression test in order to isolate the cause of
leaking cylinders.

1. Disconnect the battery ground negative cable.

2. Remove the spark plugs. Refer to Spark Plug Replacement use for the 4.3L engine.

3. Rotate the crankshaft to place the piston in the cylinder being tested at top dead center

(TDC) of the compression stroke, with both valves closed.

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

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

instructions. See Special Tools.

CAUTION: Refer to Battery Disconnect Caution .

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

prevent piston movement.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado

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:

1. Air leakage from the intake or exhaust system may indicate a worn or burnt valve or a

broken valve spring.

1. Remove the valve rocker arm cover of the suspect cylinder head. Refer to Valve

Rocker Arm Cover Replacement - Left Side or Valve Rocker Arm Cover
Replacement - Right Side .

2. Ensure that both valves are closed.

3. Inspect the cylinder head for a broken valve spring.

4. Remove and inspect the suspect cylinder head. Refer to Cylinder Head

Replacement - Left Side or Cylinder Head Replacement - Right Side .

2. Air leakage from the crankcase, oil level indicator, 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.

1. Remove the piston from the suspect cylinder. Refer to Piston, Connecting Rod,

and Bearing Removal or Piston, Connecting Rod, and Bearing
Installation .

2. Inspect the piston and connecting rod assembly. Refer to Piston, Connecting

Rod, and Bearing Cleaning and Inspection .

3. Inspect the engine block. Refer to Engine Block Cleaning and Inspection .

4. Inspect the cylinder head. Refer to Cylinder Head Cleaning and Inspection .

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

cylinder head gasket.

1. Remove both cylinder heads. Refer to Cylinder Head Replacement - Left Side

or Cylinder Head Replacement - Right Side .

2. Inspect both cylinder heads. Refer to Cylinder Head Cleaning and

Inspection .

3. Inspect the engine block. Refer to Engine Block Cleaning and Inspection .

7. Remove the J 35667-A . See Special Tools.

8. Install the spark plugs. Refer to Spark Plug Replacement use for the 4.3L engine.

IMPORTANT: Perform the leakage test on all cylinders and record the

values before doing any repairs.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado

9. Connect the battery ground negative cable.

OIL CONSUMPTION DIAGNOSIS

Excessive oil consumption, not due to leaks, is the use of 1 liter (1 quart) of engine oil within 3
200 kilometers (2,000 miles). However, during initial engine break-in periods 4 828-6 437
kilometers (3,000-4,000 miles), oil consumption may exceed 1 liter (1 quart) or more. The causes
of excessive oil consumption include the following conditions:

External oil leaks

Tighten the bolts and/or replace gaskets and oil seals as necessary.

Incorrect oil level or improper reading of oil level indicator

With the vehicle on a level surface, allow adequate drain down time and check for the
correct oil level.

Improper oil viscosity

Use recommended SAE viscosity for the prevailing temperatures.

Continuous high speed driving and/or severe usage

Crankcase ventilation system restrictions or malfunctioning components

Valve guides and/or valve stem oil seals worn, damaged, or the seal omitted

Ream the valve guides and install oversize service valves and/or new valve stem oil seals.

Piston rings broken, improperly installed, worn, or not seated properly

Allow adequate time for the piston rings to seat. Replace broken or worn piston rings as
necessary.

Piston improperly installed or miss-fitted

OIL PRESSURE DIAGNOSIS AND TESTING

1. With the vehicle on a level surface, allow adequate drain down time, 2-3 minutes, and

CAUTION: Refer to Battery Disconnect Caution .

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado

measure for a low engine oil level.

Add the recommended grade engine oil, and fill the crankcase until the oil level measures
FULL on the oil level indicator.

2. Operate the engine and verify low or no oil pressure on the vehicle oil pressure gage or the

oil indicator light.

Listen for a noisy valve train or a knocking noise.

3. Inspect for the following:

Engine oil diluted by moisture or unburned fuel mixtures

Improper engine oil viscosity for the expected temperature

Incorrect or faulty oil pressure gage sensor

Incorrect or faulty oil pressure gage

Plugged oil filter

Malfunctioning oil filter bypass valve

4. Remove the oil pressure gage sensor or another engine block oil gallery plug.

5. Install an oil pressure gage.

6. Start the engine and then allow the engine to reach normal operation temperature.

7. Measure the engine oil pressure at the following RPM:

Specification:

1. 42 kPa (6 psig) minimum, at 1,000 RPM

2. 125 kPa (18 psig) minimum, at 2,000 RPM

3. 166 kPa (24 psig) minimum, at 4,000 RPM

8. If the engine oil pressure is below minimum specifications, inspect the engine for one or

more of the following:

Oil pump worn or dirty

Malfunctioning oil pump pressure relief valve

Oil pump screen loose, plugged, or damaged

Excessive bearing clearance

Cracked, porous or restricted oil galleries

Engine block oil gallery plugs missing or incorrectly installed

Broken valve lifters

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 4.3L - Sierra & Silverado