Hummer H3. Manual — part 279

BASE ENGINE MISFIRE WITH ABNORMAL INTERNAL LOWER ENGINE NOISES

Base Engine Misfire with Abnormal Internal Lower Engine Noises

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.

Cause

Correction

Abnormalities (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.

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.

Worn Piston Rings
Oil consumption may or may not cause the
engine to misfire.

Inspect the spark plugs for oil deposits.

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

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3

BASE ENGINE MISFIRE WITH ABNORMAL VALVE TRAIN NOISE

Base Engine Misfire with Abnormal Valve Train Noise

BASE ENGINE MISFIRE WITH COOLANT CONSUMPTION

Base Engine Misfire with Coolant Consumption

Perform cylinder leak down and
compression testing to determine the
cause.

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 valve rocker arms
The rocker arm needle bearings should be
intact within the rocker arm assembly.

Replace the valve rocker arms as required.

Stuck valves
Carbon buildup on the valve stem can cause
the valve not to 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, valve lash adjusters
and rocker arms.

Sticking valve lash adjusters

Replace as required.

Cause

Correction

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

Inspect for spark plugs saturated by
coolant.

Perform a cylinder leak down test.

Inspect the cylinder head and engine
block for damage to the coolant
passages and/or a faulty head gasket.

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3

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

UPPER ENGINE NOISE, REGARDLESS OF ENGINE SPEED

Upper Engine Noise, Regardless of Engine Speed

Repair or replace as required.

Cause

Correction

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

Inspect the spark plugs for oil deposits.

Repair or replace as required.

Worn Piston Rings
Oil consumption may or may not cause the
engine to misfire.

Inspect the spark plugs for oil deposits.

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

Perform cylinder leak down and
compression testing to determine the
cause.

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.

Worn crankshaft thrust bearing

Inspect the thrust bearing and
crankshaft.

Repair or replace as required.

Damaged or faulty oil filter by-pass valve

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

Repair or replace as required.

Cause

Correction

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3

LOWER ENGINE NOISE, REGARDLESS OF ENGINE SPEED

Low oil pressure

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

Repair or replace as required.

Worn or damaged valve rocker arm

Inspect the rocker arm for wear or
missing needle bearings

Replace the valve rocker arms as
required.

Improper lubrication to the valve rocker arms Inspect the following components and repair

or replace as required:

The valve rocker arm

The valve lash adjusters

The oil filter bypass valve

The oil transfer tube

The oil pump and pump screen

The engine block oil galleries

Broken valve spring

Replace the valve spring.

Worn or dirty valve lash adjusters

Replace the valve lash adjusters.

Stretched or broken timing chain and/or
damaged sprocket teeth

Replace the timing chain and sprockets.

Worn engine camshaft lobes

Inspect the engine camshaft lobes.

Replace the camshaft, valve lash
adjusters and rocker arms as required.

Worn valve guides or valve stems

Inspect the following components and repair
as required:

The valves

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:

The valves

The valve guides

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3