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For 1990-2009 cars only
Makes 🢒 Buick 🢒 1998 🢒 Skylark 🢒 Engine 🢒 Engine Controls - 2.4L 🢒 Poor Fuel Economy

Poor Fuel Economy

Checks

Action

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 at correct pressure?
       - Are excessively heavy loads being carried?
       - Is acceleration too much, too often?

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.

Sensor/System
    • Check the oxygen sensor (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, check the O2S 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 and HO2S 2 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 the EGR valve for a stuck open pintle.
    • Check for proper operation of the MAP Sensor.
    • Check for proper operation of the TP sensor.
    • Check for proper operation of the ECT sensor.

Ignition System
    • Check for proper ignition voltage output with the spark plug jumper wires J 36012-A and spark tester J 26792 .
    • Check 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, 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 Low Coolant Level Indicator Diagnosis .
    • Check for incorrect or malfunctioning engine thermostat. Refer to Thermostat Diagnosis in Engine Cooling.

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 chamber-Leaking valve seals.
    • For incorrect basic engine parts. Inspect for the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Additional Checks
    • Check TCC operation. Refer to Torque Converter Clutch Evaluation and Diagnosis in Automatic Transaxle.
    • 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 and/or Exhaust System.