GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2000 🢒 Bonneville 🢒 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 Before Starting 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?
       - Are the tires at the correct pressure?
       - Are there excessively heavy loads being carried?
       - Is acceleration too much or too often?

Fuel System
    • Check the fuel pressure. Refer to Fuel System Pressure Test (VIN K) or to Fuel System Pressure Test (VIN 1) .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Ensure each injector harness is connected to the correct injector/cylinder. Refer to Fuel Injector Electrical Harness Removal from Rail .
    • Check for fuel in the pressure regulator vacuum hose.

Sensor/System
    • Check the intake system and the crankcase for air leaks.
    • Check for correct calibration of the speedometer. Connect a J 33431-B Signal Generator to the vehicle speed sensor (VSS) electrical connector. Turn the ignition on. Turn the tester on and monitor the speedometer.

Ignition System
    • Check for the proper ignition voltage output using the following procedure:
       - 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 connected 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 coils, check for the following conditions:

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

       - Inspect the coils for cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Secondary Resistance
5,000-8,000 ohms

       - Inspect the spark plug wires for signs of arcing or cross firing, cracks, carbon tracking, plug boot damage, pinched wires, incorrect routing, or a resistance more than the specified value.

Spark Plug Wire Resistance
3280-4921 ohms per meter (1,000-1500 ohms per 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 malfunctioning.

       - Check for a malfunctioning ignition control module.
       - Check the ignition system wiring for a loose ignition module feed, ground connection, or damaged system wiring.
    • Remove the spark plugs.
    • Inspect the spark plugs for the following conditions:
       - Fouling
       - Cracks

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

       - Check the spark plugs for signs of carbon tracing on the porcelain or arcing at the plug wire contact.
       - Check the spark plugs for incorrect gap. Refer to Maintenance Items in Maintenance and Lubrication.
       - Check the spark plugs for damaged electrodes.
       - Check the spark plugs for incorrect heat range. Refer to Maintenance Items in Maintenance and Lubrication.
    • 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 engine coolant level.
    • Check for an incorrect or malfunctioning engine thermostat. Refer to Thermostat Diagnosis in Engine Cooling.

Engine Mechanical
    • Check engine mechanical for the following:
       - Check the compression. Refer to Engine Compression Test in Engine Mechanical.
       - Check for sticking or leaking valves. Refer to Cylinder Leakage Test in Engine Mechanical.
       - Inspect for worn camshaft lobes.
       - Check the valve timing.
       - Check for bent push rods.
       - Check for worn rocker arms.
       - Check for broken valve springs.
       - Check for excessive oil in combustion chamber or leaking valve seals.
    • Inspect the following for incorrect basic engine parts:
       - Inspect the camshaft
       - Inspect the cylinder heads
       - Inspect the pistons, etc.
    • Refer to Engine Overhaul in Engine Mechanical for diagnosis procedures.

Additional Checks
    • Check TCC operation. Refer to Torque Converter Diagnosis in Automatic Transaxle-4T65-E.
    • Check the exhaust system for a restriction.
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the mufflers for heat distress or internal failure.
       - Inspect for a plugged 3-way catalytic converter. Refer to Restricted Exhaust System Check .