GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C Pickup - 2WD (CNG) 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 Lack of Power, Sluggishness, or Sponginess

Checks

Action

DEFINITION: The engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator pedal.

Preliminary Checks
    • Refer to Symptoms .
    • Compare the customer's vehicle with a similar unit. Verify that the customer has an actual problem. Do not compare the power output of the vehicle operating on natural gas to a vehicle operating gasoline as the fuels do have different drive feel characteristics.
    • Remove the air filter and inspect for dirt or restriction.
    • Inspect the transmission shift pattern and the downshift operation. Refer to Automatic Transmission in the C/K Truck Service Manual.

Sensor Checks
    • A skewed IAT sensor.
    • A skewed ECT sensor.
    • Inspect for an open NGO enable circuit.
    • Inspect the knock sensor (KS) system.

Fuel System Checks
    • Inspect for a restricted fuel filter or improper fuel. Refer to Fuel System Diagnosis .
    • Inspect for the proper ignition output voltage with the J 26792 Spark Tester or the equivalent.
    • Verify that the correct bi-fuel VCM software is installed.

Exhaust System Checks
    • Inspect the exhaust system for a possible restriction.
    • Inspect the exhaust system for damaged or collapsed pipes.
    • Inspect the muffler for heat distress or a possible internal failure.

Additional Checks
    • Verify that the Control Module grounds are clean, tight, and in their proper locations.
    • Inspect the EGR valve for being open or partially open all the time. Refer to EGR System Diagnosis in Engine Controls - 5.0, 5.7L in the C/K Truck Service Manual.
    • Inspect the A/C operation. Refer to A/C Compressor Control Circuit Diagnosis in Engine Controls - 5.0, 5.7L in the C/K Truck Service Manual.
    • Verify the Torque Converter Clutch (TCC) operation. Refer to Torque Converter Clutch Diagnosis in Automatic Transmission in the C/K Truck Service Manual.
    • Verify the generator output voltage. Refer to Engine Electrical in the C/K Truck Service Manual.
    • Inspect for a stretched throttle cable.

Engine Mechanical Check

Inspect the engine for the proper operation of the following items:

    • The engine compression
    • The valve timing
    • An improper or worn camshaft