Chevrolet Silverado / GMC Sierra. Manual - part 231
BASE ENGINE MISFIRE WITHOUT INTERNAL ENGINE NOISES
Cause
Correction
Fuel injector harness connectors are
connected to the incorrect fuel
injectors/cylinders
Relocate the fuel injector harness connectors,
as necessary.
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 and lead to a misfire diagnostic
trouble code (DTC). 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
May lead to a misfire DTC.
A misfire code may be present without an
actual misfire condition.
Inspect the components and repair or
replace, as required.
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.
Restricted exhaust system
A severe restriction in the exhaust flow can
cause significant loss of engine performance
and may set a DTC. Possible causes of
restrictions include collapsed or dented pipes
or plugged mufflers and/or catalytic
converters.
Repair or replace, as required.
Improperly installed or damaged vacuum
hoses
Repair or replace, as required.
Improper sealing between the intake manifold
and cylinder heads or throttle body
Replace the intake manifold, gaskets,
cylinder heads, and/or throttle body, as
required.
Improperly installed or damaged manifold
absolute pressure (MAP) sensor
The sealing grommet of the MAP sensor
should not be torn or damaged.
Repair or replace the MAP sensor, as
required.
2008 Hummer H2
2008 ENGINE Engine Mechanical - 6.2L - H2
Worn or loose rocker arms
The rocker arm bearing end caps and/or
needle bearings should be intact and in the
proper position.
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
the valve to not close properly.
Repair or replace, as required.
Excessively worn or mis-aligned timing chain Replace the timing chain and sprockets, as
required.
Worn camshaft lobes
Replace the camshaft and valve lifters.
Excessive oil pressure
A lubrication system with excessive oil
pressure may lead to excessive valve lifter
pump-up and loss of compression.
1. Perform an oil pressure test. Refer to
Oil Pressure Diagnosis and Testing.
2. Repair or replace the oil pump, as
required.
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. Inspect the cylinder heads, engine
block, and/or head gaskets. Refer to
Coolant in Combustion Chamber.
3. 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 identify the
cause. Refer to Cylinder Leakage
Test.
4. Repair or replace, as required.
2008 Hummer H2
2008 ENGINE Engine Mechanical - 6.2L - H2
BASE ENGINE MISFIRE WITH ABNORMAL INTERNAL LOWER ENGINE NOISES
A damaged crankshaft reluctor wheel
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.
Replace the sensor and/or crankshaft, as
required.
Improper operation of the camshaft position
(CMP) actuator and/or control system
Repair, as required. Refer to Camshaft
Position Actuator and Solenoid Valve
Diagnosis and Testing.
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
Replace the drive belt. Refer to Drive Belt
Replacement - Accessory.
2008 Hummer H2
2008 ENGINE Engine Mechanical - 6.2L - H2
BASE ENGINE MISFIRE WITH ABNORMAL VALVE TRAIN NOISE
actual misfire condition.
Worn, damaged, or mis-aligned accessory
drive components or excessive pulley runout
A misfire code may be present without an
actual misfire condition.
Inspect the components and repair or replace,
as required.
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
2008 Hummer H2
2008 ENGINE Engine Mechanical - 6.2L - H2