Hummer H3. Manual — part 486

BASE ENGINE MISFIRE WITH ABNORMAL INTERNAL LOWER ENGINE NOISES

A damaged crankshaft reluctor wheel can
result in different symptoms depending on the
severity and location of the damage.

Systems with electronic
communications, DIS or coil per
cylinder, and severe reluctor ring
damage may exhibit periodic loss of
crankshaft position, stop delivering a
signal, and then sync the crankshaft
position.

Systems with electronic communication,
DIS or coil per cylinder, and slight
reluctor ring damage may exhibit no loss
of crankshaft position and no misfire
may occur. However, a P0300 DTC
may be set.

Systems with mechanical
communications, high voltage switch,
and severe reluctor ring damage may
cause additional pulses and effect fuel
and spark delivery to the point of
generating a P0300 DTC or P0336.

required.

Cause

Correction

Abnormalities, such as severe cracking,
bumps or missing areas in the accessory drive
belt
Abnormalities in the accessory drive system
and/or components may cause engine RPM
variations, noises similar to a faulty lower
engine and also lead to a misfire condition. A
misfire code may be present without an
actual misfire condition.

Replace the drive belt. Refer to Drive Belt
Replacement - Accessory.

Worn, damaged, or mis-aligned accessory
drive components or excessive pulley runout
A misfire code may be present without an

Inspect the components and repair or replace,
as required.

2008 Hummer H3

2008 ENGINE Engine Mechanical - 5.3L - H3

BASE ENGINE MISFIRE WITH ABNORMAL VALVE TRAIN NOISE

actual misfire condition.
Loose or improperly installed engine flex
plate or crankshaft balancer
A misfire code may be present without an
actual misfire condition.

Repair or replace the flex plate and/or
balancer, as required.
Refer to Automatic Transmission Flex
Plate Replacement, or Crankshaft
Balancer Replacement.

Worn piston rings
Oil consumption may or may not cause the
engine to misfire.

1. Inspect the spark plugs for oil deposits.

Refer to Spark Plug Inspection .

2. Inspect the cylinders for a loss of

compression. Refer to Engine
Compression Test.

3. Perform cylinder leak down and

compression testing to determine the
cause. Refer to Cylinder Leakage
Test.

4. Repair or replace, as required.

Worn crankshaft thrust bearings
Severely worn thrust surfaces on the
crankshaft and/or thrust bearing may permit
fore and aft movement of the crankshaft and
create a DTC without an actual misfire
condition.

Replace the crankshaft and bearings, as
required.

Cause

Correction

Worn or loose rocker arms
The rocker arm bearing end caps and/or
needle bearings should be intact within the
rocker arm assembly.

Replace the valve rocker arms, as required.

Worn or bent pushrods

Replace the pushrods.

Inspect the top of the pistons for valve
contact. If the top of the piston shows
valve contact, replace the piston and pin
assembly.

Stuck valves
Carbon buildup on the valve stem can cause

Repair or replace, as required.

2008 Hummer H3

2008 ENGINE Engine Mechanical - 5.3L - H3

BASE ENGINE MISFIRE WITH COOLANT CONSUMPTION

BASE ENGINE MISFIRE WITH EXCESSIVE OIL CONSUMPTION

the valve to not close properly.
Excessively worn or mis-aligned timing chain Replace the timing chain and sprockets, as

required.

Worn camshaft lobes

Replace the camshaft and valve lifters.

Sticking lifters

Replace, as required.

Cut or damaged oil pump screen O-ring seal
which may cause aeration of the engine oil

Repair, as required. Refer to Oil Pressure
Diagnosis and Testing.

Cause

Correction

Faulty cylinder head gaskets and/or cracking
or other damage to the cylinder heads and
engine block cooling system passages
Coolant consumption may or may not cause
the engine to overheat.

1. Inspect for spark plugs saturated by

coolant. Refer to Spark Plug
Inspection .

2. Perform a cylinder leak down test.

Refer to Cylinder Leakage Test.

3. Inspect the cylinder heads and engine

block for damage to the coolant
passages and/or a faulty head gasket.
Refer to Coolant in Combustion
Chamber.

4. Repair or replace, as required.

Cause

Correction

Worn valves, valve guides and/or valve stem
oil seals

1. Inspect the spark plugs for oil deposits.

Refer to Spark Plug Inspection .

2. Repair or replace, as required.

Worn piston rings
Oil consumption may or may not cause the
engine to misfire.

1. Inspect the spark plugs for oil deposits.

Refer to Spark Plug Inspection .

2. Inspect the cylinders for a loss of

compression. Refer to Engine
Compression Test.

3. Perform cylinder leak down and

compression testing to determine the

2008 Hummer H3

2008 ENGINE Engine Mechanical - 5.3L - H3

ENGINE NOISE ON START-UP, BUT ONLY LASTING A FEW SECONDS

UPPER ENGINE NOISE, REGARDLESS OF ENGINE SPEED

cause. Refer to Cylinder Leakage
Test.

4. Repair or replace, as required.

Cause

Correction

Incorrect oil filter without anti-drainback
feature

Install the correct oil filter.

Incorrect oil viscosity

1. Drain the oil.

2. Install the correct viscosity oil.

High valve lifter leak down rate

Replace the lifters, as required.

Worn crankshaft thrust bearing

1. Inspect the crankshaft end play.

2. Inspect the thrust bearing and

crankshaft.

3. Repair or replace, as required.

Damaged or faulty oil filter bypass valve
The bypass valve is now internal to the oil
filter.

1. Inspect the oil filter bypass valve for

proper operation.

2. Repair or replace, as required.

Cause

Correction

Low oil pressure

1. Perform an oil pressure test. Refer to

Oil Pressure Diagnosis and Testing.

2. Repair or replace, as required.

Loose and/or worn valve rocker arm
attachments

1. Inspect the valve rocker arm, bolt, and

pedestal.

2. Repair or replace, as required.

Worn or damaged valve rocker arm

1. Inspect the rocker arm for wear or

missing needle bearings

2. Replace the valve rocker arms, as

required.

Bent or damaged push rod

Inspect the following components and
replace, as required:

2008 Hummer H3

2008 ENGINE Engine Mechanical - 5.3L - H3