GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Chevy P12 Chassis 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 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 position.

Preliminary
    • Refer to Symptoms , Important Preliminary Checks Before Starting.
    • Search for bulletins.
    • Check the PCM grounds for being clean, tight and in their proper locations. Refer to PCM wiring diagrams.
    • Be sure the driver understands the operation of the transmission and A/C compressor operation as explained in the owners manual.

Sensor/System
    • Check the Heated Oxygen Sensors (HO2S). The Heated Oxygen Sensors (HO2S) should respond quickly to different throttle positions. If they do not, check 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 Information Sensors/Switches Description .
    • Check the MAF sensor connections. Repair or replace terminals. Refer to Wiring Repairs .

Fuel System
    • Check for a low fuel pressure condition. 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 that each injector harness is connected to the correct injector/cylinder according to the firing order (firing order: 1-8-4-3-6-5-7-2). Relocate injector harnesses as necessary.
    • Check the items which can cause an engine to run rich (long term fuel trim near -13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1 .
    • Check the items that can cause an engine to run lean (long term fuel trim near 23%). For a lean condition, refer to DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 and DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 .

Ignition System
    • Wet down the secondary ignition system with water from a spray bottle. Wetting down the secondary ignition system may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as you apply the water.
    • Check for proper ignition voltage output with spark tester J 26792 . Refer to Electronic Ignition (EI) System Diagnosis .
    • Remove the spark plugs and check for the following:
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • An improper spark plug gap will cause a driveability problem. Refer to Engine Electrical/Spark Plugs. Do the spark plug gapping using a wire gauge gap tool (J 41319). Refer to Spark Plug Replacement. Determine the cause of the fouling before replacing the spark plugs if spark plugs are gas or oil fouled. Refer to Fuel System Diagnosis for diagnosis of the rich condition or Engine/Engine Mechanical for diagnosis of the oil fouling condition.
    • Check for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .
    • Check the spark plugs for proper heat range. Refer to Spark Plug Visual Diagnosis .

Engine Mechanical

Ensure that the engine coolant temperature 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 a lack of power, miss, or rough idle. If the vehicle operates in Engine Coolant Over temperature-Fuel Disabled Mode, refer to Engine/Engine Cooling for diagnosis.

Additional Checks
    • Visually (physically) check vacuum hoses for splits, kinks, and proper connections and routing as shown on Vehicle Emission Control Information label.
    • Check for an intermittent EGR problem. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .
    • Check the generator output voltage.