GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2000 🢒 Sunfire 🢒 Engine 🢒 Engine Controls - 2.4L 🢒 Poor Fuel Economy

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 Symptoms .
    • Search for service bulletins.
    • Check owners driving habits.
       - Is A/C ON full time (Defroster mode ON)?
       - Are tires correct size and at the correct pressure?
       - Are excessively heavy loads being carried?
       - Is acceleration too much, too often?
       - Check the brakes to ensure that the brakes are not dragging.

Fuel System
    • Check the fuel pressure. Refer to Fuel System Diagnosis .
    • Check the fuel injectors. Refer to Fuel Injector Balance Test .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Ensure each injector harness is connected to the correct injector/cylinder. Refer to Engine Controls Schematics .
    • Check for fuel in the pressure regulator vacuum hose.
    • Check for proper operation of the Evaporative Emission (EVAP) control system. Refer to Evaporative Emission Control System Diagnosis .

Sensor/System
    • Check the Oxygen sensor (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, check the O2S 1 for silicon or other contaminants from fuel or the use of improper RTV sealant. The sensor may have a white powdery coating. Silicon contamination causes a high but false O2S 1 signal voltage (rich exhaust indication). The PCM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Refer to Oxygen sensor in Information Sensors/Switches Description .
    • Check for proper operation of the MAP Sensor. Refer to Manifold Absolute Pressure Sensor Output Diagnosis .
    • Check for proper operation of the TP sensor.
    • Check for proper operation of the ECT sensor.
    • Check for the proper operation of the speedometer.

Ignition System
    • Check the knock sensor for proper operation to make sure that the engine timing is not being retarded.
    • Check for proper ignition voltage output with the J 36012-A spark plug jumper wires and J 26792 spark tester or equivalent.
    • Check the spark plugs for the following conditions:
       - Check for wet or fuel fouled spark plugs.
       - Check for cracks on the spark plugs.
       - Check for wear.
       - Check for improper spark plug gap.
       - Check for burned electrodes or heavy deposits.
       - Proper heat range.
    • If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
    • Check the Ignition Control Module (ICM) for proper ground connection.
    • Check the ignition coils for cracks or carbon tracking.

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

Engine Mechanical
    • Check engine mechanical for the following:
       - Low compression.
       - Sticking or leaking valves.
       - Worn camshaft lobes.
       - Valve timing.
       - Broken valve springs.
       - Excessive oil in combustion chamber-Leaking valve seals.
    • For incorrect basic engine parts. Inspect for the following:
       - Camshafts
       - Cylinder head
       - Pistons, etc.

Additional Checks
    • Check for the proper operation of the transaxle and the TCC. Refer to Road Test for 4T40 or Road Test for 3T40 in Automatic Transmission.
    • Check the exhaust system for air leaks before or near the O2S 1 sensor
    • Check exhaust system for possible restriction. 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 converter. Refer to Restricted Exhaust System Check .
    • Check for proper operation of the brake system, making sure the brake are not dragging.