GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Impala 🢒 Engine 🢒 Engine Electrical 🢒 Surges/Chuggles

Checks

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.
    • Refer to Visual/Physical Checks.
    • Search for bulletins.
    • Ensure 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 clutch operates.

Sensor/System
    • Test the heated oxygen sensors (HO2S). The heated oxygen sensors should respond quickly to different throttle positions. If not, inspect the HO2S for silicon or other contaminants from fuel or use of improper RTV sealant. The sensors may have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). 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 related wiring.
    • Test 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 .
    • Ensure each injector harness is connected to the correct injector/cylinder.
    • Inspect items which can cause an engine to run rich (long term fuel trim is significantly in the negative range). Refer to Diagnostic Aids for DTC P0172 .
    • Inspect items that can cause an engine to run lean (long term fuel trim is significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 .

Ignition System
    • Test for proper ignition voltage output using the following steps:
        1. Clip the J 26792 spark tester to engine ground.
        2. Connect one end of a spark plug wire to the spark tester. Leave the other end of the spark plug wire connected to the coil being tested.
        3. Connect another spark plug wire between the remaining tower of the coil being tested and ground.
        4. Crank the engine while observing the spark tester. A crisp blue spark should be observed.
        5. Repeat the above steps for each coil.
    • If spark is not present at the coils, test for the following conditions:
       - Coils--Cracks, carbon tracking/arcing, or a secondary resistance value outside the specified range

Coil Resistance
5,000-8,000 ohms (5K-8K ohms)

       - Spark plug wires--Signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range

Spark Plug Wire Resistance Regular
9,840 ohms per meter (3,000 ohms per foot)

Spark Plug Wire Resistance Police
1,968 ohms per meter (600 ohms per foot)

   Important: Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition components will arc to ground when a secondary component is faulty.

       - Defective module
       - Ignition system wiring--Loose ignition module feed or ground connection, or damaged system wiring
    • Remove spark plugs and inspect for the following:
       - Fouled plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned or damaged electrodes
       - Improper heat range or reach
    • If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to Spark Plug Inspection .

Additional Checks
    • Test TCC operation. Refer to Torque Converter Diagnosis in Automatic Transaxle-4T65-E.
    • Test exhaust system for possible restriction:
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the muffler for heat distress or possible internal failure.
       - Test for a possible plugged 3-way catalytic converter by inspecting the exhaust system backpressure. Refer to Restricted Exhaust in Engine Exhaust.