GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1998 🢒 DeVille 🢒 Engine 🢒 Engine Controls - 4.0L and 4.6L 🢒 Lack of Power, Sluggishness, or Sponginess

Lack of Power, Sluggish or Spongy

Checks

Action

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

Preliminary Checks
    • Refer to Symptoms .
    • Search for bulletins.
    • Check PCM grounds for being clean, tight and in their proper locations.
    • Remove and check air filter element for dirt, or for being restricted. Replace as necessary.

Fuel System Checks
    • Check for low fuel pressure. Refer to Fuel System Pressure Test .
    • Check for restricted fuel filter.
    • Check for contaminated fuel. Refer to Fuel Quality Diagnosis .
    • Check items which can cause an engine to run rich (long term fuel trim near -99%).
    • Check items that can cause an engine to run lean (long term fuel trim near 100%).

Sensor/System Checks
    • Using a scan tool, monitor KS system for excessive spark retard activity.
    • Check the EGR system for proper operation.

Ignition System
    • Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as water is applied.
    • Check for proper ignition voltage output with spark tester J 26792. Refer to Secondary Ignition Diagnosis .
    • Remove spark plugs and check for the following:
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • An improper spark plug gap will cause a driveability problem. The spark plug gapping should be done using a wire gauge gap tool (J 41319). If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
    • Check for loose ignition control module ground.
    • Spark plugs for proper heat range. Refer to the owner's manual for the proper replacement of spark plugs.

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

Additional Checks
    • Check exhaust system for possible restrictions. Check for the following:
       - Inspect exhaust system for damaged or collapsed pipes.
       - Inspect mufflers for heat distress or possible internal failure.
       - For possible plugged Three-Way catalytic converters by comparing exhaust system back pressure on each side of engine. Refer to Restricted Exhaust System Check in Engine Exhaust.
    • Check Torque Converter Clutch (TCC) for proper operation.
    • Traction Control system brake switch assembly. Loss of performance can result from an improperly adjusted or a failed extended travel brake switch. The PCM operates in the Torque Management mode when the PCM detects the brake pedal and throttle are depressed at the same time.