GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2004 🢒 DeVille 🢒 Engine 🢒 Engine Controls - 4.6L 🢒 Surges/Chuggles

Inspection/Test

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.

Preliminary
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.

Be sure that the driver understands 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 system operate.

Sensor/System
    • Inspect the heated oxygen sensors (HO2S)s. The HO2Ss should respond quickly to different throttle positions. If they do not, check the HO2S for the following conditions:
       - Contaminants from the fuel
       - Improper use of RTV
       - The sensors may have a white powdery coating. This will result in a high but false signal voltage (rich exhaust indicated). The powertrain control module (PCM) will reduce the amount of fuel delivered to the engine causing a severe driveability condition.
    • Inspect the mass air flow (MAF) sensor and intake air system for proper connections.
    • Inspect the exhaust gas recirculation (EGR) system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description

Fuel System
    • Test the fuel pressure. Refer to Fuel System Diagnosis .
    • Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Inspect the following that may cause the engine to run rich:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

    • Any water intrusion in the HO2S connector.
    • Engine oil contaminated by fuel.
    • An EVAP canister purge condition.
    • Incorrect fuel pressure--Refer to Fuel System Diagnosis .
    • A leaking fuel pressure regulator.
    • Inaccurate MAF sensor.
    • Blockage on the inlet screen of the MAF sensor.
    • Vacuum hoses for splits, kinks and proper connections.
    • The air intake duct for being collapsed or restricted.
    • 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.

    • Any water intrusion into the HO2S connector.
    • An exhaust leak between the HO2S and the engine--Refer to Exhaust Leakage in Engine Exhaust.
    • Any vacuum leaks.
    • Incorrect fuel pressure--Refer to Fuel System Diagnosis .
    • An inaccurate mass air flow (MAF) sensor.
    • Fuel Contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Vacuum hoses for splits, kinks and proper connections.

Ignition System
    • Test for proper ignition voltage output using the J 26792 Spark Tester.
    • Inspect for damaged ignition coils within the ignition coil module assemblies.
    • Inspect for damaged or misaligned spark plug boots.
    • Inspect for a missing or damaged ignition module ground spring.
    • Inspect the spark plugs. Refer to Spark Plug Inspection .

Additional
    • Inspect the vacuum hoses for splits, kinks, and improper connections or routing.
    • Inspect torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis in Automatic Transaxle.
    • Inspect for a restrictive exhaust system. Refer to Restricted Exhaust .