Hummer H2. Manual — part 1696

BASE ENGINE MISFIRE WITH ABNORMAL INTERNAL LOWER ENGINE NOISES

Base Engine Misfire with Abnormal Internal Lower Engine Noises

Engine Cooling in Engine Cooling.
Coolant consumption may or may not cause the engine to
overheat.

6.0L.

z

Inspect the cylinder heads, engine
block, and/or head gaskets. Refer to
Coolant in Combustion Chamber .

z

Repair or replace as required.

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

z

Inspect the spark plugs for oil
deposits. Refer to Spark Plug
Inspection in Engine Controls -
6.0L.

z

Inspect the cylinders for a loss of
compression. Refer to Engine
Compression Test .

z

Perform cylinder leak down and
compression testing to identify the
cause. Refer to Cylinder Leakage
Test .

z

Repair or replace as required.

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

z

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.

z

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.

z

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.

Cause

Correction

Abnormalities, such as severe cracking, bumps or missing
areas in the accessory drive belt
Abnormalities in the accessory drive system and/or

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

2004 Hummer H2

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

BASE ENGINE MISFIRE WITH ABNORMAL VALVE TRAIN NOISE

Base Engine Misfire with Abnormal Valve Train Noise

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.
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, repair or
replace as required.

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

Repair or replace the flywheel and/or
balancer as required.
Refer to Engine Flywheel Replacement
or Crankshaft Balancer Replacement .

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

z

Inspect the spark plugs for oil
deposits. Refer to Spark Plug
Inspection in Engine Controls -
6.0L.

z

Inspect the cylinders for a loss of
compression. Refer to Engine
Compression Test .

z

Perform cylinder leak down and
compression testing to determine
the cause. Refer to Cylinder
Leakage Test .

z

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

z

Replace the pushrods.

z

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 not to close properly.

Repair or replace as required.

2004 Hummer H2

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

BASE ENGINE MISFIRE WITH COOLANT CONSUMPTION

Base Engine Misfire with Coolant Consumption

BASE ENGINE MISFIRE WITH EXCESSIVE OIL CONSUMPTION

Base Engine Misfire with Excessive Oil Consumption

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

Engine Noise on Start-Up, but Only Lasting a Few Seconds

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.

Cause

Correction

Faulty cylinder head gaskets and/or cracking or other
damage to the cylinder heads and engine block
cooling system passages - Refer to Diagnostic
Starting Point - Engine Cooling in Engine Cooling.
Coolant consumption may or may not cause the
engine to overheat.

z

Inspect for spark plugs saturated by
coolant. Refer to Spark Plug Inspection in
Engine Controls - 6.0L.

z

Perform a cylinder leak down test. Refer to
Cylinder Leakage Test .

z

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 .

z

Repair or replace as required.

Cause

Correction

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

z

Inspect the spark plugs for oil deposits. Refer to Spark Plug
Inspection in Engine Controls - 6.0L.

z

Repair or replace as required.

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

z

Inspect the spark plugs for oil deposits. Refer to Spark Plug
Inspection in Engine Controls - 6.0L.

z

Inspect the cylinders for a loss of compression. Refer to
Engine Compression Test .

z

Perform cylinder leak down and compression testing to
determine the cause. Refer to Cylinder Leakage Test .

z

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.

2004 Hummer H2

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

UPPER ENGINE NOISE, REGARDLESS OF ENGINE SPEED

Upper Engine Noise, Regardless of Engine Speed

2. Install the correct viscosity oil.

High valve lifter leak down rate

Replace the lifters as required.

Worn crankshaft thrust bearing

1. Check the crankshaft end play.

2. Inspect the thrust bearing and crankshaft.

3. Repair or replace as required.

Damaged or faulty oil filter by-pass valve

z

Inspect the oil filter by-pass valve for proper
operation.

z

Repair or replace as required.

Cause

Correction

Low oil pressure

z

Perform an oil pressure test. Refer to Oil Pressure
Diagnosis and Testing .

z

Repair or replace as required.

Loose and/or worn valve rocker arm
attachments

z

Inspect the valve rocker arm, bolt, and pedestal.

z

Repair or replace as required.

Worn or damaged valve rocker arm

z

Inspect the rocker arm for wear or missing needle bearings

z

Replace the valve rocker arms as required.

Bent or damaged push rod

Inspect the following components and replace as required:

z

The valve rocker arm

z

The valve push rod

z

The valve lifter

z

The valve lifter guide

z

The piston

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

Improper lubrication to the valve
rocker arms

Inspect the following components and repair or replace as
required:

z

The valve rocker arm

z

The valve push rod

z

The valve lifter

z

The oil filter bypass valve

z

The oil pump and pump screen

2004 Hummer H2

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2