GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 LeSabre 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Poor Fuel Economy

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DEFINITION: Fuel economy, as measured by an actual road test is noticeably lower than expected. Also, economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.

Preliminary
    • Refer to Important Preliminary Checks in Symptoms .
    • Refer to Visual/Physical Checks in Symptoms .
    • Search for bulletins.
    • Check the owner's driving habits.
       - Is the A/C ON full-time (Defroster mode ON)?
       - Are the tires at the correct pressure?
       - Are excessively heavy loads being carried?
       - Is the acceleration too much, too often?

Fuel System
    • Check the fuel pressure. Refer to Fuel System Pressure Test (VIN K) .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Ensure each injector harness is connected to the correct injector and cylinder.
    • Check for fuel in the pressure regulator vacuum hose.

Sensor/System
    • Check the air intake system and the crankcase for air leaks. Refer to Air Intake System Description and to Crankcase Ventilation System Description .
    • Check for proper calibration of the speedometer. Connect a J 33431-C signal generator to the vehicle speed sensor (VSS) electrical connector. Turn the ignition and the tester ON and monitor the speedometer.

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 spark should be observed.
       - Repeat the above steps for each coil.
    • If spark is not present at the plugs, check for the following conditions:
       - Check the coils for cracks, carbon tracking/arcing, or a secondary resistance value outside the specified range.

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

       - Check the spark plug wires for signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.

Spark Plug Wire Resistance
1000 to 1500 ohms/foot.

   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 faulty.

       - Check for a defective module.
       - Check the ignition system wiring for a loose ignition module feed or ground connection, or damaged system wiring.
    • Remove the spark plugs and check for the following:

   Important: If carbon tracking is detected on any component, replace that component and the component's mate.

       - Carbon tracking on the porcelain and pitting on the plug wire contact.
       - Fouled plugs
       - Cracks
       - Improper gap
       - Burned or damaged electrodes
       - Improper heat range or reach. Refer to Maintenance Items .
    • If the spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

Engine Cooling System
    • Check the engine coolant level for being low. Refer to Loss of Coolant .
    • Check for an incorrect or faulty engine thermostat. Refer to Thermostat Diagnosis .

Engine Mechanical
    • Check engine mechanical for the following:
       - Check compression.
       - Sticking or leaking valves.
       - Worn camshaft lobes.
       - Valve timing.
       - Bent push rods.
       - Worn rocker arms.
       - Broken valve springs.
       - Excessive oil in combustion chambers or leaking valve seals.
    • For incorrect basic engine parts. Inspect for the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Base Engine Misfire Diagnosis for diagnostic procedures.

Additional Checks
    • Check the TCC operation. Refer to Torque Converter Diagnosis .
    • Check the exhaust system for possible restriction. Check for the following:
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the mufflers for heat distress or an internal failure.
       - Check for a plugged three-way catalytic converter. Refer to Restricted Exhaust System Check .