GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Yukon XL - 2WD 🢒 Engine 🢒 Engine Electrical 🢒 Lack of Power, Sluggishness, or Sponginess

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 - Engine Controls .
    • 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 . 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 fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • Check the items that cause an engine to run rich long term fuel trim near -13 percent. For a rich condition, refer to DTC P0172 or P0175 .
    • Check the items that can cause an engine to run lean long term fuel trim near 24 percent For a lean condition, refer to DTC P0171 or P0174 .

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
    • 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 and listen for arcing or misfiring as water is applied.
    • Check for proper ignition voltage output with J 26792 Spark Tester .
    • 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 Inspection .
    • 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 .
    • Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant, or oil fouled. Refer to one of the following procedures:
       - For diagnosis of the rich condition, refer to DTC P0172 or P0175 .
       - For diagnosis of coolant or oil fouled spark plugs, refer to Spark Plug Inspection .
    • 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 Engine Controls Schematics .

Engine Mechanical
    • Ensure that the engine coolant temperature is not above 130°C (266°F). This condition causes the powertrain control module (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 8.1L.
    • Low cylinder compression--Refer to Engine Compression Test in Engine Mechanical 8.1L.
    • Inspect the following components for incorrect basic engine parts:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.

Refer to the appropriate procedures in Engine Mechanical 8.1L.

Additional Checks
    • 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
       - The mufflers for heat distress or possible internal failure
       - The 3-way catalytic converters for possible plugged conditions--Compare the exhaust system back pressure on each side of engine. Check back pressure by removing secondary air injection (AIR) check valves near exhaust manifolds. Refer to Restricted Exhaust in Engine Exhaust.
    • Check the transmission torque converter clutch (TCC) for proper operation. Refer to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission in Automatic Transmission-4L80-E or Diagnostic System Check - Automatic Transmission in Automatic Transmission-Allison.