GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 TopKick C-Series (Conventional) C6/C7/C8 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Lack of Power, Sluggishness, or Sponginess

Inspections

Action

DEFINITION: Engine delivers less than expected power. Little or no increase in speed when the accelerator pedal is pushed down part way.

Preliminary
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Ensure that the power take off (PTO) switch is in the OFF position.
    • Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views and Engine Controls Schematics .
    • Remove the air filter element and inspect for dirt or for being restricted. Refer to Air Cleaner Element Replacement and replace as necessary.

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 .
    • Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test and Fuel Injector Balance Test with Special Tool .
    • 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 .
       - 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 .
       - 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

Sensor/System

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
    • Wet down the secondary ignition system with water from a spray bottle. Wetting the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as water is applied.
    • Test for proper ignition voltage output with J 26792 Spark Tester.
    • 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
    • Excessive oil in combustion chamber--Leaking valve seals. Refer to Oil Consumption Diagnosis .
    • Low cylinder compression--Refer to Engine Compression Test .
    • Inspect the following components for incorrect basic engine parts:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • 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 . This could result in any of the following conditions:
       - A no start
       - A start and stall
       - Erratic performance

Refer to the appropriate procedures in Engine Mechanical.

Additional

Inspect the following components of the exhaust system for possible restrictions:

    • The exhaust system for damaged or collapsed pipes
    • The exhaust manifold for a collapsed inner wall
    • Compare the exhaust system back pressure on each side of engine. Refer to Restricted Exhaust .