GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1997 🢒 Sonoma Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 Surges/Chuggles

Checks

Action

Definition: The engine has a power variation under a steady throttle or cruise. The vehicle feels as if it speeds up and slows down with no change in the accelerator pedal.

Preliminary Checks
    • Refer to Important Preliminary Checks .
    • Be sure the driver understands the Torque Converter Clutch operation.
    • Be sure the driver understands the A/C Compressor operation.
    • Use the scan tool to make sure the reading of the Vehicle Speed Sensor (VSS) matches the vehicle speedometer. This excludes vehicles with electronic transmissions where some variation between the VSS and the speedometer is normal. Refer to the following items:
       -  DTC P0506 Idle Speed Low
       -  DTC P0507 Idle Speed High

Sensor Check

Check the (Heated) Oxygen Sensor (HO2S) performance. Refer to the following items:

Fuel System Checks
    • Check for a Rich or Lean symptom that causes the condition. Drive the vehicle at the speed of the complaint. Monitoring the Fuel Trim will help identify the problem.
    • Lean - The Long Term Fuel Trim will be greater than 150. Refer to the following items:
       -  DTC P0132 HO2S Circuit High Voltage Sensor 1 for the Diagnostic Aids
       -  DTC P0138 HO2S Circuit High Voltage Sensor 2 for the Diagnostic Aids.
    • Rich - The Long Term Fuel Trim will be less than 115. Refer to the following items:
       -  DTC P0131 HO2S Circuit Low Voltage Sensor 1 for the Diagnostic Aids
       -  DTC P0137 HO2S Circuit Low Voltage Sensor 2 for the Diagnostic Aids.
    • Check the fuel pressure while the condition exists. Refer to Fuel System Pressure Test .
    • Check the in-line fuel filter for a restrictions.

Ignition System Checks
    • Check for the proper ignition output voltage using the spark tester J 26792 or the equivalent. Refer to Enhanced Ignition System Diagnosis .
    • Check the spark plugs. Remove the plugs and inspect them for the following conditions:
       - Wetness
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • Check the Crankshaft Position (CKP) sensor. Refer to Enhanced Ignition System Diagnosis (Overview) .

Additional Checks
    • Check the Control Module grounds for being clean, tight, and in their proper locations.
    • Check the generator output voltage.
    • Check the vacuum hoses for kinks or leaks. Refer to the Vehicle Emission Control Information label.
    • Check for an intermittent EGR problem. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .
    • Check for Torque Converter Clutch (TCC) operation. Refer to Transmission Section 7.