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 🢒 Surges/Chuggles

Inspections

Action

DEFINITION: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal position.

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 Power and Grounding Component Views and Engine Controls Schematics .
    • Ensure that the driver understands the operation of the transmission torque converter clutch (TCC) and A/C compressor operation as explained in the owners manual. Inform the customer how the TCC and the A/C clutch operates.

Sensor/System
    • Inspect the heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions. If they do not, inspect the HO2S for silicon or other contaminates from fuel or the use of improper RTV sealant. The sensors may have a white, powdery coating and result in a high but false signal voltage rich exhaust indication. The PCM will then reduce the amount of fuel delivered to the engine causing a severe driveability problem. For more information, refer to Oil Consumption Diagnosis .
    • Inspect the mass air flow (MAF) sensor connections. Repair or replace terminals. Refer to Connector Repairs .

Fuel System
    • Test the system for leaks or restrictions. Refer to Fuel System Diagnosis .
    • Test for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Verify that each injector harness is connected to the correct injector or cylinder. Relocate injector harnesses as necessary.
    • 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 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

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

Test engine mechanical for the following:

    • Low compression--Refer to Engine Compression Test .
    • Sticking or leaking valves
    • Worn camshaft lobes
    • Valve timing
    • Bent push rods
    • Worn rocker arms
    • Broken valve springs
    • Excessive oil in combustion chamber--Leaking valve seals. Refer to Oil Consumption Diagnosis .
    • 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

Transmission

Inspect the transmission and clutch for proper operation.

Additional
    • Exhaust system--Refer to Diagnostic Starting Point - Engine Exhaust .
    • A/C system--Refer to Air Conditioning (A/C) System Performance Test .
    • Inspect vacuum hoses for splits, kinks, and proper connections and routing as shown on Vehicle Emission Control Information label.
    • Inspect air intake ducting for proper installation--Refer to Air Cleaner Outlet Front Duct Replacement .