GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Envoy - 2WD 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Surges/Chuggles

Inspections

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 position.

Preliminary Inspections
    • Refer to Symptoms - Engine Controls .
    • Be sure that the driver understands the torque converter clutch operation.
    • Be sure that the driver understands the A/C compressor operation.
    • Ensure that the transmission fluid is at the proper level.

Sensor/System

Display the scan tool parameters for the various engine controls sensors. Inspect for any abnormal readings.

Fuel System
    • Inspect 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 condition.
       - Lean--The long term fuel trim will be more than 150.
       - Rich--The long term fuel trim will be less than 115.
    • Test the fuel pressure while the condition exists. Refer to Fuel System Diagnosis .
    • Inspect the in-line fuel filter for a restrictions.

Ignition System

Inspect the spark plugs. Remove the plugs and inspect for the following conditions:

    • Wetness
    • Cracks
    • Wear
    • Improper gap
    • Burned electrodes
    • Heavy deposits
        Refer to Spark Plug Inspection .

Additional
    • Inspect the control module grounds for being clean, tight, and in their proper locations. Refer to Power and Grounding Component Views .
    • Test the generator output voltage. Refer to Diagnostic System Check - Vehicle .
    • Inspect the vacuum hoses for kinks or leaks.
    • Inspect the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis .
    • Inspect the exhaust system for a possible restriction. Refer to Restricted Exhaust .