GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Sierra - 4WD 🢒 Engine 🢒 Engine Controls - 4.8L, 5.3L, and 6.0L 🢒 Lack of Power, Sluggishness, or Sponginess

Lack of Power, Sluggish or Spongy

Checks

Action

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

Preliminary Checks
    • Refer to Important Preliminary Checks Before Starting in Symptoms .
    • Search for bulletins.
    • Check the PCM grounds for being clean, tight and in the proper locations. Refer to Engine Controls Schematics .
    • Remove the air filter element and check for dirt or for being restricted. Refer to Air Cleaner Element Replacement and replace as necessary.

Fuel System
    • Check both 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.
    • Check for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Check for a restricted fuel filter. Refer to Fuel System Diagnosis .
    • Check for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check the items that cause an engine to run rich (long term fuel trim near -13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1 .
    • Check the items that can cause an engine to run lean (long term fuel trim near 24%). For a lean condition, refer to DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 and DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 .

Sensor/System

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

Ignition System
    • Check both 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 circuit and the injector circuits for an intermittent short to ground.
    • 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/listen for arcing or misfiring as water is applied.
    • Check for proper ignition voltage output with spark tester J 26792 .
    • Remove the spark plugs and check for the following:
       - Correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits

Refer to Spark Plug Visual Diagnosis in Engine Electrical.

    • An improper spark plug gap will cause a driveability problem. Gap the spark plugs using a wire gauge gap tool (J 41319). Refer to Spark Plug Replacement in Engine Electrical.
    • Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant, or oil fouled. Refer to DTC P0172 Fuel Trim System Rich Bank 1 or DTC P0175 Fuel Trim System Rich Bank 2 for diagnosis of the rich condition. Refer to Spark Plug Visual Diagnosis in Engine Electrical for diagnosis of coolant or oil 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 use the DTC P0300 table for diagnosis.
    • Check for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

Engine Mechanical
    • Ensure that the engine coolant temperature is not above 130°C (266°F). This condition causes the PCM to operate in Engine Coolant Over temperature-Fuel Disabled Mode. While in Engine Coolant Over temperature-Fuel Disabled Mode, the PCM will disable the fuel injectors to four cylinders at a time to keep engine temperatures from reaching damaging levels. The system perceives the Engine Coolant Over temperature-Fuel Disabled Mode as a lack of power, miss, or rough idle. If the vehicle operates in Engine Coolant Over temperature-Fuel Disabled Mode, refer to Engine Overheating in Engine Cooling for diagnosis.
    • Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical 4.8L, 5.3L, 6.0L.
    • Low cylinder compression. Refer to Engine Compression Test in Engine Mechanical 4.8L, 5.3L, 6.0L.
    • For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.

Refer to Engine/Engine Mechanical.

Additional Checks
    • Check the exhaust system for possible restrictions. Check for the following:
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the exhaust manifold for a collapsed inner wall.
       - Inspect the mufflers for heat distress or possible internal failure.
       - Inspect for possible plugged Three-Way catalytic converters by comparing exhaust system back pressure on each side of engine. Check back pressure by removing AIR check valves near exhaust manifolds. Refer to Restricted Exhaust System Check in Engine Exhaust.
    • Check the Transmission Torque Converter Clutch (TCC) for proper operation. Refer to Functional Test in Automatic Transmission 4L60E or to Functional Test in Automatic Transmission 4L80E.