GM Service Manual Online
For 1990-2009 cars only

Checks

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

Preliminary Checks

    • Search for bulletins.

Fuel System

    • Check the follwing items
    • Check for incorrect fuel pressure.
       - Refer to Fuel Pump Electrical Circuit Diagnosis .
       - Check the fuel injectors.
       - Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
       - Check items which can cause an engine to run rich (long term fuel trim is significantly in the negative range). Refer to Diagnostic Aids for DTC P0172 Fuel Trim System Rich Bank 1 .
       - Check items that can cause an engine to run lean (long term fuel trim is significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean Bank 1 .

Sensor/System

    • Using a scan tool, monitor KS system for excessive spark retard activity.
    • Check the EGR valve for a stuck open pintle. Refer to Exhaust Gas Recirculation Valve Replacement .
    • Check for a restricted intake duct or a dirty air cleaner element. Refer to Air Cleaner Element Replacement .

Ignition System

    • Check for proper ignition voltage output using the following steps:
       - Clip the spark tester J 26792 to engine ground.
       - Connect one end of a spark plug wire to the spark tester; leave the other end of the spark plug wire to the coil being tested.
       - Connect one end of another spark plug wire to the other coil tower; connect the other end of the spark plug wire to ground.
       - Crank the engine while observing the spark tester; a crisp blue spark should be observed.
       - Repeat the above steps for each coil.
    • If adequate spark is not present at the coil(s), check for the following conditions:
    • Coil(s) - Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Secondary Resistance
5000 - 8000 ohms (5K - 8K ohms)

    • Spark Plug wires - Signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, incorrect routing, or a resistance value greater than the specified value.

VIN 1 Spark Plug Wires Resistance
7000 ohms (7K ohms)

VIN K Spark Plug Wires Resistance
10000 ohms (10K ohms)

       Important: Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition components will arc to ground when a secondary component is malfunctioning.

    • Malfunctioning ignition control module.
    • Ignition System Wiring - Loose ignition module feed or ground connection, or damaged system wiring.
    • Remove spark plugs and check for the following conditions:
       - Fouled plugs
       - Cracks
       - Wear
       - Incorrect gap
       - Burned or damaged electrodes
       - Incorrect heat range
    • If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

Engine Mechanical

    • Excessive oil in combustion chamber-Leaking valve seals. Refer to Engine Mechanical.
    • Low cylinder compression. Refer to Engine Mechanical.
    • For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    •  Refer to Engine Mechanical.

Additional Checks

    • Check the exhaust system for a possible restriction.
    • Inspect the exhaust system for damaged or collapsed pipes.
    • Inspect the muffler for heat distress or possible internal failure.
    • Check for a plugged three-way catalytic converter. Refer to Restricted Exhaust System Check and/or Exhaust System .
    • Check for proper TCC operation. Refer to 4L60-E Automatic Transmission Diagnosis .