GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2002 🢒 Sunfire 🢒 Engine 🢒 Engine Electrical 🢒 Poor Fuel Economy

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DEFINITION: The fuel economy, measured by an actual road test, is noticeably lower than expected. The fuel economy, measured by an actual road test, is also noticeably lower than previous fuel economy.

Preliminary
    • Refer to Symptoms - Engine Controls .
    • Search for service bulletins.
    • Check the owner's driving habits.
       - Is the A/C ON full time, with the defroster mode ON?
       - Are the tires the correct size and at the correct pressure?
       - Is the tire pressure correct?
       - Is the vehicle carrying excessively heavy loads?
       - Is the acceleration too heavy and too frequent?
    • Check the brakes. Ensure that the brakes are not dragging.

Fuel System
    • Check the fuel pressure. Refer to Fuel System Diagnosis .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Ensure that each injector harness is connected to the correct injector and 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.

Sensor/System

Check for the following conditions:

    • The oxygen sensor (O2S 1)--The O2S 1 should respond quickly to different throttle positions. If the sensor does not respond, check it for silicon, or for other contaminants from the fuel or from the use of an improper RTV sealant. The sensor may have a white powdery coating. Silicon contamination causes a high but false O2S 1 signal voltage, indicating a rich exhaust indication. The powertrain control module (PCM) will reduce the amount of fuel that is delivered to the engine, causing a severe driveability problem.
    • Check for proper operation of the following components:
       - The manifold absolute pressure (MAP) sensor
       - The throttle position (TP) sensor
       - The engine coolant temperature (ECT) sensor
       - The speedometer

Ignition System

Check for the following conditions:

    • The knock sensor:
       - Check for proper operation.
       - Ensure that the engine timing is not being retarded.
    • The ignition voltage output--Use the J 36012-A Spark Plug Jumper Wires, and use the J 26792 Spark Tester, or equivalent.
    • The spark plugs for the following conditions:
       - Wet spark plugs
       - Fuel-fouled spark plugs
       - Cracked spark plugs
       - Worn spark plugs
       - Improper spark plug gap
       - Burned electrodes
       - Heavy deposits
       - Proper heat range
    • If the spark plugs are fuel or oil-fouled, determine the cause of the fouling before you replace the spark plugs.
    • The ignition control module (ICM) for proper ground connection
    • 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 an incorrect thermostat and for a malfunctioning engine thermostat. Refer to the Thermostat Diagnosis in Engine Cooling.

Engine Mechanical

Check the engine mechanical components for the following conditions:

    • Low compression
    • Sticking valves
    • Leaking valves
    • Improper valve timing
    • Worn camshaft lobes
    • Broken valve springs
    • Excessive oil in the combustion chamber, caused by leaking valve seals
    • Inspect the basic engine parts for incorrect components, including the following:
       - The camshaft
       - The cylinder head
       - The pistons
       - Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Additional Checks

Check for the following conditions:

    • Proper operation of the transaxle and the torque converter clutch (TCC). Refer to Road Test in Automatic Transmission.
    • The exhaust system for air leaks in front of or near the O2S 1 sensor
    • The exhaust system for restrictions-Check for the following conditions:
       - The exhaust system-Check for damaged pipes and check for collapsed pipes.
       - The mufflers--Inspect for heat distress and inspect for possible internal failure.
       - The 3-way catalytic converter--Inspect for plugs. Refer to Restricted Exhaust in Engine Exhaust.
    • Check for proper operation of the brake system. Ensure that the brakes are not dragging.