GM Service Manual Online
For 1990-2009 cars only

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 Diagnostic System Check - Vehicle .
    • Refer to Symptoms - Engine Controls .
    • Compare the customers vehicle with a similar unit in order to determine if the customer has an actual problem.
    • Remove the air filter element and check for dirt or restrictions.
    • Check the air inlet duct for any blockage or restrictions.
    • Check the transmission shift pattern and down-shift operation.

Sensor/System

Inspect the mass air flow (MAF) sensor operation. Run the engine to normal operating temperature. Turn OFF all accessories and observe the MAF sensor at idle with a scan tool. If the MAF sensor reading is more than 3.5 g/s refer to DTC P0101 .

Fuel System Checks

    • Check for a restricted fuel filter or incorrect fuel pressure.
    • Check the fuel injectors. Perform the following procedures:
       - The Fuel Injector Balance Test--Refer to Fuel Injector Balance Test with Special Tool .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Ignition System Checks

    • Check for the proper ignition voltage output with a J 26792 Spark Tester.
    • Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection .
    • Check the knock sensor (KS) and the sensor circuit shielding. A faulty knock sensor or signal interference could cause excessive retard of the ignition timing advance. Observe the spark parameter on a scan tool and compare with a known good vehicle. A typical value with the transmission in OD at 98 km/h (60 mph) with all engine accessories off is 26-32 degrees.

Exhaust System Checks

    • Check the exhaust system for a possible restriction. Refer to Restricted Exhaust .
    • Inspect the exhaust system for damaged or collapsed pipes. Inspect the muffler for heat distress or a possible internal failure.

Engine Mechanical Check

    • Check for any of the following engine mechanical problems:
       - Low compression
       - Incorrect valve timing
       - Incorrect or worn camshaft

Additional Checks

    • Check the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics .
    • Check the generator output voltage.