GM Service Manual Online
For 1990-2009 cars only

Inspection/Test

Action

DEFINITION: Engine delivers less than expected power. Little or no increase in speed when the accelerator pedal is pushed down part way.

Preliminary

    â€¢ Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    â€¢ Search for bulletins.

Sensor/System

    â€¢ Inspect the knock system (KS) for excessive spark retard.
    â€¢ Inspect the exhaust gas recirculation (EGR) system for proper operation.
    â€¢ Inspect for a dirty or damaged air cleaner element.
    â€¢ Inspect for collapsed, or damaged intake air ducting.

Fuel System

    â€¢ Test the fuel pressure. Refer to Fuel System Diagnosis .
    â€¢ Test the fuel injectors. Refer to the following:
    â€¢ Inspect for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Inspect the following that may cause the engine to run rich:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

    â€¢ Any water intrusion in the HO2S connector
    â€¢ Engine oil contaminated by fuel
    â€¢ An EVAP canister purge condition
    â€¢ Incorrect fuel pressure--Refer to Fuel System Diagnosis .
    â€¢ A leaking fuel pressure regulator
    â€¢ Any rich fuel injectors--Refer to Fuel Injector Balance Test with Tech 2 and Fuel Injector Balance Test with Special Tool .
    â€¢ Inaccurate MAF sensor
    â€¢ Blockage on the inlet screen of the MAF sensor
    â€¢ Vacuum hoses for splits, kinks and proper connections
    â€¢ The air intake duct for being collapsed or restricted
    â€¢ The air filter for being dirty or restricted--Refer to Air Cleaner Element Replacement

Inspect the following that may cause the engine to run lean:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

    â€¢ Any water intrusion into the HO2S connector
    â€¢ An exhaust leak between the HO2S and the engine--Refer to Exhaust Leakage in Engine Exhaust.
    â€¢ Any vacuum leaks
    â€¢ Incorrect fuel pressure--Refer to Fuel System Diagnosis .
    â€¢ Any lean fuel injectors--Refer to Fuel Injector Balance Test with Tech 2 and Fuel Injector Balance Test with Special Tool .
    â€¢ An inaccurate mass air flow (MAF) sensor
    â€¢ Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    â€¢ Vacuum hoses for splits, kinks and proper connections

Ignition System

    â€¢ Inspect for proper connections at each ignition module assembly.
    â€¢ Test for proper ignition voltage output using the J 26792 Spark Tester .
    â€¢ Inspect the ignition coils for cracks or damage.
    â€¢ Inspect for a missing or damaged ignition module assembly grounding spring.
    â€¢ Inspect for damaged or misaligned spark plug boots.
    â€¢ Inspect the spark plugs. Refer to Spark Plug Inspection .

Engine Mechanical

    â€¢ Inspect for excessive oil in the combustion chamber-leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical - 4.6L.
    â€¢ Inspect for low cylinder compression. Refer to Engine Compression Test in Engine Mechanical - 4.6L.
    â€¢ Inspect for incorrect basic engine parts. Inspect the following:
       - Camshafts
       - Cylinder heads
       - Pistons, etc.

Automatic Transaxle

Inspect for proper operation of the transmission fluid pressure (TFP) manual valve switch. Refer to Harsh Garage Shift or Engine Hesitation on Acceleration in Automatic Transaxle - 4T80-E.

Additional

    â€¢ Inspect the exhaust system for possible restrictions. Refer to Restricted Exhaust .
    â€¢ Inspect for proper torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis in Automatic Transaxle - 4T80-E.
    â€¢ Inspect for conditions that cause the engine torque management system to reduce engine power.