GM Service Manual Online
For 1990-2009 cars only

Inspections

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

    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .

Sensor/System

Test the manifold absolute pressure (MAP) sensor operation. Refer to Manifold Absolute Pressure Sensor Diagnosis .

Fuel System

    • Test for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect both fuel injector fuses for being open. An open injector fuse causes four ignition coils and four injectors not to operate. Replace the fuse. Inspect the ignition coil circuits and the injector circuits for an intermittent short to ground.
    • Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test and Fuel Injector Balance Test with Tech 2 .
    • Inspect the following that may cause the engine to run rich:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

       - Water intrusion in the 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 .
       - Rich fuel injectors--Refer to Fuel System Diagnosis .
       - Inaccurate mass air flow (MAF) sensor--Refer to Scan Tool Data List .
       - Blockage on the inlet screen of the MAF sensor--Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .
       - Vacuum hoses for splits, kinks and proper connections
       - The air intake duct for being collapsed or restricted--Refer to Air Cleaner Outlet Front Duct Replacement .
       - The air filter for being dirty or restricted--Refer to Air Cleaner Element Replacement .
    • Inspect the following that may cause the engine to run lean:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

       - 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 .
       - Lean fuel injectors--Refer to Fuel System Diagnosis .
       - An inaccurate MAF sensor--Refer to Scan Tool Data List .
       - Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
       - Vacuum hoses for splits, kinks and proper connections

Ignition System

    • Wet down the secondary ignition system with water from a spray bottle. Wetting down the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water.
    • Test for proper ignition voltage output with J 26792 spark tester. Refer to Electronic Ignition (EI) System Diagnosis for the procedure.
    • Remove the spark plugs and inspect for the following conditions. Refer to Spark Plug Inspection :
       - Correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • An improper spark plug gap will cause a driveability problem. Gap the spark plugs using a wire gage gap tool. Refer to Spark Plug Replacement .
    • Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant, or oil fouled. Refer to Spark Plug Inspection for diagnosis of fouled spark plugs.
    • Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a cylinder can be located with a misfire, refer to Electronic Ignition (EI) System Diagnosis for diagnosis.
    • Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

Engine Mechanical

Inspect for excessive crankshaft endplay that will cause the CKP sensor reluctor wheel to move out of alignment with the CKP sensor. Refer to Crankshaft and Bearing Cleaning and Inspection in Engine Mechanical - 8.1L. This could result in any of the following conditions:

    • A no start
    • A start and stall
    • Erratic performance

Engine Cooling System

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

Additional

Test the generator output voltage. Refer to Diagnostic System Check - Engine Electrical in Engine Electrical.