Hummer H2. Manual - part 1593

spark retard activity.

Ignition System

Inspect for proper ignition voltage output with the J 26792 Spark Tester. Refer to
Electronic Ignition (EI) System Diagnosis for procedure.

Remove spark plugs and check for the following:

{

Wet plugs

{

Cracks

{

Wear

{

Improper gap

{

Burned electrodes

{

Heavy deposits

Refer to Spark Plug Inspection .

An improper spark plug gap will cause a driveability problem. Refer to Spark
Plug Inspection . Gap the spark plugs using a wire gauge gap tool. Refer to
Spark Plug Replacement .

Determine the cause of the fouling before replacing the spark plugs.

Visually and physically inspect secondary ignition for the following:

{

Ignition wires arcing to ground

{

Ignition wires for proper routing

Soak the secondary ignition system with water from a spray bottle. Soaking the
secondary ignition system may help locate damaged or deteriorated components.
Look and listen for arcing or misfiring as you apply water.

Monitor the Misfire Current Counters while driving the vehicle in the conditions
that the misfire occurred. If a misfiring cylinder can be located, use the DTC
P0300 table for diagnosis. Refer to DTC P0300 .

Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System
Diagnosis .

Engine
Mechanical

Inspect engine mechanical for the following:

{

Compression - Refer to Engine Compression Test in Engine Mechanical.

{

Sticking or leaking valves

{

Worn camshaft lobes

{

Valve timing

{

Bent push rods

{

Worn rocker arms

{

Broken valve springs

{

Excessive oil in combustion chamber or leaking valve seals - Refer to Oil
Consumption Diagnosis in Engine Mechanical.

For incorrect basic engine parts. Inspect the following:

{

The camshaft - Refer to Camshaft and Bearings Cleaning and

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

DIESELING, RUN-ON

Dieseling, Run-On

Inspection in Engine Mechanical.

{

The cylinder heads - Refer to Cylinder Head Cleaning and Inspection in
Engine Mechanical.

{

The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings
Cleaning and Inspection in Engine Mechanical.

Inspect for excessive crankshaft endplay that will cause the crankshaft position
(CKP) sensor reluctor wheel to move out of alignment with the CKP sensor.
Refer to Crankshaft and Bearings Cleaning and Inspection in Engine
Mechanical. This could result in any of the following conditions:

{

A no start

{

A start and stall

{

Erratic performance

Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnosis
procedures.

Additional
Inspections

Inspect the exhaust system for possible restrictions. Inspect for the following:

{

Inspect the exhaust system for damaged or collapsed pipes.

{

Inspect the mufflers for heat distress or possible internal failure.

{

Inspect for possible plugged catalytic converters. Refer to Restricted
Exhaust in Engine Exhaust.

Electromagnetic interference (EMI) on the reference circuit can cause an engine
miss condition. A scan tool can usually detect EMI by monitoring the engine
RPM. A sudden increase in RPM with little change in actual engine RPM change
indicates that EMI is present. If a problem exists, inspect routing of secondary
ignition wires or high voltage components near the ignition control circuits.

Inspect the park neutral position (PNP) switch circuit. Refer to Park/Neutral
Position Switch Adjustment in Automatic Transmission - 4L60-E/4L65-E.

Inspect for faulty motor mounts. Refer to Engine Mount Inspection in Engine
Mechanical.

Inspect the intake manifold and the exhaust manifold passages for casting flash.

Inspections

Action

DEFINITION: Engine continues to run after key is turned OFF, but runs very rough. If the engine runs
smooth, inspect the ignition switch and the ignition switch adjustment.
Preliminary
Inspections

Refer to Important Preliminary Inspections Before Starting in Symptoms -
Engine Controls .

Search for bulletins.

Verify that the powertrain control module (PCM) grounds are clean, tight, and in

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

BACKFIRE

Backfire

the proper locations. Refer to Power and Grounding Component Views in
Wiring Systems and Engine Controls Schematics .

Fuel System

Inspect the fuel injectors for a leaking condition. Refer to Fuel System Diagnosis for
the proper procedure.

Inspections

Actions

DEFINITION: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping
noise.
Preliminary
Inspections

Refer to Important Preliminary Inspections Before Starting in Symptoms -
Engine Controls .

Search for bulletins.

Verify that the powertrain control module (PCM) grounds are clean, tight, and in
the proper locations. Refer to Power and Grounding Component Views in
Wiring Systems and Engine Controls Schematics .

Fuel System

Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis .

Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-
Fuel Diagnosis (without Special Tool and E85) or Alcohol/Contaminants-in-
Fuel Diagnosis (with Special Tool) .

Inspect the fuel injectors. Refer to Fuel Injector Coil Test , Fuel Injector
Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 .

Verify that each injector harness is connected to the correct injector or cylinder.
Relocate injector harnesses as necessary.

Sensor/System

Inspect the air intake system and crankcase for air leaks.

Inspect the crankcase ventilation valve for proper operation. Refer to Crankcase
Ventilation System Inspection/Diagnosis in Engine Mechanical.

Inspect for an inaccurate speedometer. Refer to Symptoms - Instrument Panel,
Gauges and Console in Instrument Panel, Gauges, and Console.

Use a scan tool in order to monitor the knock sensor (KS) system for excessive
spark retard activity. Refer to Knock Sensor (KS) System Description .

Ignition System

Inspect for proper ignition voltage output with J 26792 Spark Tester.

Remove spark plugs and inspect for the following:

{

Wet plugs

{

Cracks

{

Wear

{

Improper gap

{

Burned electrodes

{

Heavy deposits

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

Refer to Spark Plug Inspection .

An improper spark plug gap will cause a driveability problem. Refer to Spark
Plug Inspection . Gap the spark plugs using a wire gauge gap tool. Refer to
Spark Plug Replacement .

Determine the cause of the fouling before replacing the spark plugs. Refer to
Spark Plug Inspection for diagnosis.

Visually and physically inspect secondary ignition for the following:

{

Ignition wires arcing to ground

{

Ignition coils arcing to ground

Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System
Diagnosis .

Engine Cooling
System

Inspect the engine coolant level for being low. Refer to Loss of Coolant in
Engine Cooling.

Inspect the engine thermostat for proper operation and for the correct heat range.
Refer to Thermostat Diagnosis in Engine Cooling.

Engine
Mechanical

Inspect engine mechanical for the following:

{

Compression - Refer to Engine Compression Test in Engine Mechanical.

{

Sticking or leaking valves

{

Worn camshaft lobes

{

Valve timing

{

Bent push rods

{

Worn rocker arms

{

Broken valve springs

{

Excessive oil in combustion chamber or leaking valve seals - Refer to Oil
Consumption Diagnosis in Engine Mechanical.

For incorrect basic engine parts. Inspect the following:

{

The camshaft - Refer to Camshaft and Bearings Cleaning and
Inspection in Engine Mechanical.

{

The cylinder heads - Refer to Cylinder Head Cleaning and Inspection in
Engine Mechanical.

{

The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings
Cleaning and Inspection in Engine Mechanical.

Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnosis

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

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