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

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 is also noticeably lower than fuel economy was on the vehicle at one time, as previously shown by a road test.

Preliminary
    • Refer to Symptoms - Engine Controls .
    • Search for service bulletins.
    • Review the owner's driving habits.
       - Is the air conditioning (A/C) ON full time, or is the 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
    • Inspect the fuel pressure. Refer to Fuel System Diagnosis .
    • Inspect the fuel injectors. Refer to Fuel Injector Balance Test with Special Tool , or Fuel Injector Balance Test with Tech 2 .
    • Inspect for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Ensure that each injector harness is connected to the correct injector/cylinder. Refer to Engine Controls Schematic Icons .
    • Inspect for fuel in the pressure regulator vacuum hose.
    • Ensure proper operation of the evaporative emission (EVAP) control system.

Sensor/System
    • Inspect the oxygen sensor (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, inspect the O2S 1 for silicon or for other contaminants from the fuel or from the use of an improper room-temperature vulcanizing (RTV) sealant. The sensors may have a white powdery coating indicative of silicon contamination, which may cause a high but false O2S 1 signal voltage, indicating a rich exhaust. The powertrain control module (PCM) will reduce the amount of fuel that is delivered to the engine, causing a severe driveability problem.
    • Ensure proper operation of:
       - The manifold absolute pressure (MAP) sensor
       - The throttle position (TP) sensor
       - The engine coolant temperature (ECT) sensor

Ignition System
    • Ensure proper ignition voltage output with the J 26792 Spark Tester or equivalent.
    • Inspect the spark plugs for the following conditions:
       - Wet or fuel-fouled spark plugs
       - Cracks on the spark plugs
       - Wear
       - Improper spark plug gap
       - Burned electrodes or heavy deposits
    • If the spark plugs are fuel or oil-fouled, determine the cause of the fouling before replacing the spark plugs.
    • Inspect the ignition control module (ICM) for proper ground connection.
    • Inspect the ignition coils for cracks or carbon tracking.
    • Inspect the spark plug wires for proper resistance and condition.

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

Engine Mechanical
    • Inspect for the following conditions:
       - Incorrect compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Incorrect valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber due to leaking valve seals
    • Inspect the engine for incorrect basic engine parts. Inspect the following:
       - The camshaft
       - The cylinder heads
       - The pistons
       - Other engine parts as appropriate
    • Refer to Diagnostic Starting Point - Engine Mechanical in Engine Mechanical 2.2L.

Additional Checks
    • Inspect the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis in Transmission/Transaxle.
    • Inspect the exhaust system for possible restrictions. Inspect for the following:
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the mufflers for heat distress or possible internal failure.
       - Inspect for a possible plugged three-way catalytic converter (TWC). Refer to Restricted Exhaust in Engine Exhaust.