Hummer H2. Manual — part 1697
LOWER ENGINE NOISE, REGARDLESS OF ENGINE SPEED
Lower Engine Noise, Regardless of Engine Speed
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The engine block oil galleries
Broken valve spring
Replace the valve spring and spring shim.
Worn or dirty valve lifters
Replace the valve lifters.
Stretched or broken timing chain
and/or damaged sprocket teeth
Replace the timing chain and sprockets.
Worn engine camshaft lobes
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Inspect the engine camshaft lobes.
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Replace the camshaft and valve lifters as required.
Worn valve guides or valve stems
Inspect the following components and repair as required:
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The valves
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The valve guides
Stuck valves
Carbon on the valve stem or valve seat
may cause the valve to stay open.
Inspect the following components and repair as required:
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The valves
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The valve guides
Cause
Correction
IMPORTANT:
A cold piston knock which disappears in 1.5 minutes should be considered acceptable. A cold
engine knock usually disappears when the specific cylinder's secondary ignition circuit is grounded
out during diagnosis.
A low rumble/knocking may indicate a crankshaft or piston, lower engine, concern.
Low oil pressure
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Perform an oil pressure test. Refer to Oil
Pressure Diagnosis and Testing .
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Repair or replace damaged components as
required.
Worn accessory drive components
Abnormalities such as severe cracking, bumps or
missing areas in the accessory drive belt and/or
misalignment of system components.
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Inspect the accessory drive system.
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Repair or replace as required.
Loose or damaged crankshaft balancer
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Inspect the crankshaft balancer.
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Repair or replace as required.
Detonation or spark knock
Verify the correct operation of the ignition controls
system. Refer to Detonation/Spark Knock in
Engine Controls - 6.0L.
Loose torque converter bolts
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Inspect the torque converter bolts and
flywheel.
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Repair or replace as required.
2004 Hummer H2
2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2
ENGINE NOISE UNDER LOAD
Engine Noise Under Load
Loose or damaged flywheel
Repair or replace the flywheel.
Oil pump screen loose, damaged or restricted
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Inspect the oil pump screen.
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Repair or replace as required.
Excessive piston-to-cylinder bore clearance
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Inspect the piston and cylinder bore.
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Repair as required.
Excessive piston pin-to-bore clearance
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Inspect the piston, pin, and connecting rod.
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Replace the piston, pin and connecting rod
as an assembly, as required.
Excessive connecting rod bearing clearance
Inspect the following components, and repair as
required:
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The connecting rod bearings
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The connecting rods
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The crankshaft
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The crankshaft journals
Excessive crankshaft bearing clearance
Inspect the following components, and repair as
required:
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The crankshaft bearings
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The crankshaft journals
Incorrect piston, piston pin and connecting rod
installation
Pistons must be installed with the mark or dimple on
the top of the piston facing the front of the engine.
Piston pins must be centered in the connecting rod
pin bore.
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Verify the pistons, piston pins and
connecting rods are installed correctly. Refer
to Piston, Connecting Rod, and Bearing
Installation .
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Repair as required.
Cause
Correction
Low oil pressure
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Perform an oil pressure test. Refer to Oil Pressure Diagnosis and
Testing .
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Repair or replace as required.
Detonation or spark knock
Verify the correct operation of the ignition controls. Refer to
Detonation/Spark Knock in Engine Controls - 6.0L.
Loose torque converter bolts
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Inspect the torque converter bolts and flywheel.
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Repair as required.
Cracked flywheel - automatic
transmission
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Inspect the flywheel bolts and flywheel.
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Repair as required.
2004 Hummer H2
2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2
ENGINE WILL NOT CRANK - CRANKSHAFT WILL NOT ROTATE
Engine Will Not Crank - Crankshaft Will Not Rotate
Excessive connecting rod
bearing clearance
Inspect the following components, and repair as required:
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The connecting rod bearings
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The connecting rods
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The crankshaft
Excessive crankshaft bearing
clearance
Inspect the following components, and repair as required:
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The crankshaft bearings
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The crankshaft journals
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The cylinder block crankshaft bearing bore
Cause
Correction
Seized accessory drive
system component
1. Remove the accessory drive belts.
2. Confirm that the engine will rotate. Rotate the crankshaft by hand
at the crankshaft balancer or flywheel location.
3. Repair or replace the components as required.
Seized automatic
transmission torque converter
1. Remove the torque converter-to-flywheel bolts.
2. Confirm that the engine will rotate. Rotate the crankshaft by hand
at the crankshaft balancer or flywheel location.
3. Repair or replace the components as required.
Broken timing chain
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Inspect the timing chain and gears.
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Repair or replace the components as required.
Seized timing chain or timing
gears
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Inspect the timing chain and gears for foreign material or a seized
chain.
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Repair or replace the components as required.
Seized or broken camshaft
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Inspect the camshaft and the camshaft bearings.
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Repair or replace the components as required.
Bent valve in the cylinder
head
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Inspect the valves and the cylinder heads.
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Repair or replace the components as required.
Seized oil pump
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Inspect the oil pump assembly.
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Repair or replace as required.
Hydraulically locked cylinder
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Coolant/antifreeze in
the cylinder
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Oil in the cylinder
1. Remove spark plugs and check for fluid in the cylinder. When
rotating the engine with the spark plugs removed, the piston, on
compression stroke, will push fluid from the combustion chamber.
Refer to Coolant in Combustion Chamber .
2. Inspect for failed/broken head gaskets.
2004 Hummer H2
2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2
COOLANT IN COMBUSTION CHAMBER
Coolant in Combustion Chamber
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Fuel in the cylinder
3. Inspect for a cracked engine block or cylinder head.
4. Inspect for a sticking fuel injector.
5. Repair or replace the components as required.
Material in the cylinder
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Broken valve
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Broken piston rings
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Piston material
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Foreign material
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Inspect the cylinder for damaged components and/or foreign
materials.
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Repair or replace the components as required.
Seized crankshaft or
connecting rod bearings
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Inspect crankshaft and connecting rod bearings.
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Repair or replace the components as required.
Bent or broken connecting
rod
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Inspect the connecting rods.
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Replace the piston, pin and connecting rod as an assembly, as
required.
Broken crankshaft
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Inspect the crankshaft.
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Repair or replace the components as required.
Cause
Correction
DEFINITION: Excessive white smoke and/or coolant type odor coming from the exhaust pipe may
indicate coolant in the combustion chamber. Low coolant levels, an inoperative cooling fan, or a faulty
thermostat may lead to an "overtemperature" condition which may cause engine component damage.
1. A slower than normal cranking speed may indicate coolant entering the combustion chamber.
Refer to Engine Will Not Crank - Crankshaft Will Not Rotate .
2. Remove the spark plugs and inspect for spark plugs saturated by coolant or coolant in the cylinder
bore.
3. Inspect by performing a cylinder leak-down test. During this test, excessive air bubbles within the
coolant may indicate a faulty gasket or damaged component.
4. Inspect by performing a cylinder compression test. Two cylinders "side-by-side" on the engine
block, with low compression, may indicate a failed cylinder head gasket. Refer to Engine
Compression Test .
Cracked intake
manifold or failed
gasket
Replace the components as required.
Faulty cylinder head
gasket
Replace the head gasket and components as required. Refer to Cylinder Head
Cleaning and Inspection and Cylinder Head Replacement - Left or Cylinder
Head Replacement - Right .
Warped cylinder
Machine the cylinder head to the proper flatness, if applicable and replace the
2004 Hummer H2
2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2
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