GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 XLR 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 Surges/Chuggles

Inspection/Tests

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 Inspections Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Inspect the engine control module (ECM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics .
    • Verify 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

Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section.

    • 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.
    • Inspect the mass air flow (MAF) sensor for any contamination on the sensing element.
    • Inspect the air intake ducts for being collapsed, damaged, loose, improperly installed , or leaking especially between the MAF sensor and the throttle body.
    • Inspect for proper operation of the manifold absolute pressure (MAP) sensor. Refer to Scan Tool Data Definitions .
    • Inspect for an engine coolant temperature (ECT) sensor that has shifted in value . Refer to Temperature Versus Resistance .

Fuel System
    • Test for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Test the fuel injectors. Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Solenoid Coil Test .
    • Inspect 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 for the following conditions 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--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
       - An evaporative emission (EVAP) canister purge condition
       - Incorrect fuel pressure--Refer to Fuel System Diagnosis .
       - Leaking fuel injectors--Refer to Fuel System Diagnosis .
       - For proper operation of the MAP sensor--Refer to Scan Tool Data Definitions .
       - For proper operation of the MAF sensor
       - Blockage on the inlet screen of the MAF sensor
       - Vacuum hoses that are split, kinked, or improperly connected
       - An air intake duct that is collapsed or restricted
       - An air filter that is dirty or restricted--Refer to Air Cleaner Element Replacement .
    • Inspect for the following conditions 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 .
       - Restricted fuel injectors--Refer to Fuel Injector Balance Test with Special Tool .
       - For proper operation of the MAP sensor--Refer to Scan Tool Data Definitions .
       - For proper operation of the MAF sensor
       - Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
       - Vacuum hoses that are split, kinked, or improperly connected

Ignition System
    • Soak the secondary ignition system with water from a spray bottle. Soaking 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 the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis .
    • Remove the spark plugs and inspect for the following conditions:
       - 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 gage gap tool. Refer to Ignition System Specifications and Spark Plug Replacement .
    • Determine the cause of the fouling before replacing the spark plugs.
    • Monitor the Misfire Current Counters while driving the vehicle within the conditions that the misfire occurred.
    • Inspect for loose ignition coil grounds.
    • Inspect the ignition coils for cracks or carbon tracking.

Additional Inspections
    • Visually and physically inspect vacuum hoses for splits, kinks, and proper connections and routing as shown on the Vehicle Emission Control Information label.
    • Inspect the transmission TCC operation.
    • Test the A/C clutch for proper operation. Refer to Symptoms - HVAC Systems - Automatic in HVAC Systems - Automatic.
    • Inspect the exhaust system for possible restrictions. Refer to Restricted Exhaust in Engine Exhaust.