Hummer H2. Manual - part 1590

HESITATION, SAG, STUMBLE 

Hesitation, Sag, Stumble 

Inspection in Engine Mechanical.  

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

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

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Refer to Symptoms - Engine Mechanical in Engine Mechanical.  

Additional 
Inspections

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Inspect the park/neutral position (PNP) switch operation. Refer to Diagnostic 
System Check - Automatic Transmission in Automatic Transmission - 
4L60-E.  

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Inspect the transmission torque converter clutch (TCC) operation. The TCC 
applying too soon can cause the engine to spark knock. Refer to Diagnostic 
System Check - Automatic Transmission in Automatic Transmission - 
4L60-E.  

Inspection/Tests

Action

DEFINITION: Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle 
speed. Usually more pronounced when first trying to make the vehicle move, as from a stop. May cause 
the engine to stall if severe enough.
Preliminary

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

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Search for bulletins.  

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

Sensor/System

Inspect the manifold absolute pressure (MAP) sensor operation.

Fuel System

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

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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) .  

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Verify that both fuel injector fuses are not open. An open fuel injector fuse 
causes 4 ignition coils and 4 fuel injectors not to operate. Inspect the ignition 
coil circuits and the fuel injector circuits for an intermittent short to ground. 
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Replace the 
fuse.  

z

Inspect for the following that may cause the engine to run rich: 

NOTE:

Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and 
Notices.

 

2004 Hummer H2 

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

  

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Water intrusion in the heated oxygen sensor (HO2S) connector  

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Engine oil contaminated by fuel  

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An evaporative emission (EVAP) canister purge condition  

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Incorrect fuel pressure - Refer to Fuel System Diagnosis .  

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Leaking fuel injectors - Refer to Fuel System Diagnosis .  

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An inaccurate mass air flow (MAF) sensor  

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Blockage on the inlet screen of the MAF sensor - Refer to Mass Air 
Flow (MAF)/Intake Air Temperature (IAT) Sensor Replacement .  

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Vacuum hoses that are split, kinked, or improperly connected  

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An air intake duct that is collapsed or restricted-Refer to Air Cleaner 
Resonator Outlet Duct Replacement .  

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An air filter that is dirty or restricted - Refer to Air Cleaner Element 
Replacement .  

z

Inspect for the following conditions that may cause the engine to run lean: 

{

Water intrusion in the HO2S connector  

{

An exhaust leak between the HO2S and the engine-Refer to Exhaust 
Leakage in Engine Exhaust.  

{

Vacuum leaks  

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Incorrect fuel pressure - Refer to Fuel System Diagnosis .  

{

Restricted fuel injectors - Refer to Fuel Injector Balance Test with 
Special Tool or Fuel Injector Balance Test with Tech 2 .  

{

An inaccurate MAF sensor  

{

Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis 
(without Special Tool and E85) or Alcohol/Contaminants-in-Fuel 
Diagnosis (with Special Tool) .  

{

Vacuum hoses that are split, kinked, or improperly connected  

NOTE:

Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and 
Notices.

Ignition System

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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.  

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

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Remove the spark plugs and check for the following: 

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Correct heat range  

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Wet plugs  

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Cracks  

 

2004 Hummer H2 

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

  

CUTS OUT, MISSES 

Cuts Out, Misses 

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Wear  

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Improper gap  

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Burned electrodes  

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Heavy deposits  

Refer to Spark Plug Inspection . 

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

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

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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 .  

z

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

Engine Cooling 
System

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

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: 

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A no start  

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A start and stall  

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Erratic performance  

Additional 
Inspections

Inspect the generator output voltage. Refer to Diagnostic System Check - Engine 
Electrical in Engine Electrical for the procedure. Repair the charging system if the 
generator output voltage is less than 9 volts or more than 16 volts.

Inspections

Action

DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine 
load increases. This condition is not normally felt above 1,500 RPM or 48 km/h (30 mph). The exhaust 
has a steady spitting sound at idle or low speed.
Preliminary

z

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

z

Search for bulletins.  

z

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 .  

 

2004 Hummer H2 

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

  

z

Remove the air filter element and inspect for dirt and for restrictions. Refer to 
Air Cleaner Element Replacement . Replace as necessary.  

Fuel System

z

Inspect the fuel injectors. Refer to Fuel Injector Coil Test .  

z

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

z

Inspect for a restricted fuel filter. Refer to Fuel System Diagnosis .  

z

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) .  

z

Inspect for the following that may cause the engine to run rich: 

{

Water intrusion in the heated oxygen sensor (HO2S) connector  

{

Engine oil contaminated by fuel  

{

An evaporative emission (EVAP) canister purge condition  

{

Incorrect fuel pressure - Refer to Fuel System Diagnosis .  

{

A leaking fuel pressure regulator - Refer to Fuel System Diagnosis .  

{

Leaking fuel injectors - Refer to Fuel System Diagnosis .  

{

An inaccurate mass air flow (MAF) sensor  

{

Blockage on the inlet screen of the MAF sensor - Refer to Mass Air Flow 
(MAF)/Intake Air Temperature (IAT) Sensor Replacement .  

{

Vacuum hoses that are split, kinked, or improperly connected  

{

An air intake duct that is collapsed or restricted - Refer to Air Cleaner 
Resonator Outlet Duct Replacement .  

{

An air filter that is dirty or restricted - Refer to Air Cleaner Element 
Replacement .  

z

Inspect for the following conditions that may cause the engine to run lean: 

{

Water intrusion in the HO2S connector  

{

An exhaust leak between the HO2S and the engine - Refer to Exhaust 
Leakage in Engine Exhaust.  

{

Vacuum leaks  

{

Incorrect fuel pressure - Refer to Fuel System Diagnosis .  

{

Restricted fuel injectors - Refer to Fuel Injector Balance Test with 
Special Tool or Fuel Injector Balance Test with Tech 2 .  

NOTE:

Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and 
Notices.

NOTE:

Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and 
Notices.

 

2004 Hummer H2 

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