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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 757 (ENGINE CONTROLS (TROUBLESHOOTING & DIAGNOSIS) -- 5.7L)TROUBLESHOOTINGSURGES/CHUGGLES
1999 GMC Forward Control 5.7 R, Automatic

Section 757 (Engine Controls (Troubleshooting & Diagnosis) -- 5.7L): Troubleshooting: Surges/Chuggles

1999 GMC Forward Control 5.7 R, AutomaticSECTION Surges/Chuggles
WARNING: This page is about a different car, the 2004 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
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 powertrain control module (PCM) 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
  • 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. For more information, refer to Oil Consumption Diagnosis in Engine Mechanical.
  • Inspect the mass air flow (MAF) sensor connections. Repair or replace damaged terminals. Refer to Connector Repairs in Wiring Systems.
Fuel System
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:
    • 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.
  • Monitor the Misfire Current Counters while driving the vehicle within the conditions that the misfire occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 .
  • Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis  .
Engine Mechanical Verify that the engine coolant temperature (ECT) 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 turns fuel OFF to four cylinders at a time to keep engine temperatures from reaching damaging levels. The system perceives Engine Coolant Over Temperature-Fuel Disabled Mode as 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.
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. Refer to Emission Hose Routing Diagram .
  • Inspect the transmission torque converter clutch (TCC) operation. A TCC applying too soon can cause the engine to spark knock. Refer to Diagnostic Starting Point - Automatic Transmission in Automatic Transmission (4L60-E).
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.