GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2000 🢒 S/T Isuzu - 4WD 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 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.
    • Verify 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
    • Test for proper fuel pressure. Refer to Fuel System Diagnosis .
    • Test the fuel injectors. Refer to Fuel Injector Balance Test .
    • Test 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 .
    • Inspect for fuel in the pressure regulator vacuum hose.
    • Test for proper operation of the evaporative emission (EVAP) control system.

Sensor/System
    • The O2S 1 should respond quickly to different throttle positions. If not, inspect the O2S 1 for silicon or other contaminants from fuel or the use of improper RTV sealant. The sensors 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 .
    • Test for proper operation of the following sensors:
       - MAP
       - TP
       - ECT

Ignition System
    • Test for proper ignition voltage output with a J 26792 Spark Tester or equivalent.
    • Inspect the spark plugs for the following conditions:
       - Wet or fuel fouled
       - Cracks
       - Wear
       - Improper gap
       - Burnt 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.
    • Inspect the ignition control module (ICM) for proper ground connection.
    • Test the ignition coils for cracks or carbon tracking.
    • Test/inspect the spark plug wires for proper resistance and condition.

Engine Cooling System
    • Inspect for proper engine coolant level.
    • Inspect/test for incorrect or malfunctioning engine thermostat. Refer to Thermostat Diagnosis in Engine Cooling.

Engine Mechanical
    • Inspect engine mechanical for the following conditions:
       - Compression, refer to Engine Compression Test in Engine Mechanical
       - Sticking or leaking valves, refer to Valve Train Diagnosis in Engine Mechanical
       - Worn camshaft lobes, refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical
       - Valve timing, refer to Camshaft Timing Chain and Sprocket Cleaning and Inspection in Engine Mechanical
       - Bent push rods, refer to Valve Train Diagnosis in Engine Mechanical
       - Worn rocker arms, refer to Valve Train Diagnosis in Engine Mechanical
       - Broken valve springs, refer to Valve Train Diagnosis in Engine Mechanical
       - Excessive oil in combustion chamber -- Leaking valve seals, refer to Oil Consumption Diagnosis in Engine Mechanical
    • For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.

Additional Checks
    • Test TCC operation. Refer to Torque Converter Diagnosis in Automatic Transmission.
    • Inspect the exhaust system for the following conditions:
       - Inspect exhaust system for damaged or collapsed pipes.
       - Inspect mufflers for heat distress or possible internal failure.
       - Inspect for possible plugged three-way catalytic converter. Refer to Restricted Exhaust System Check in Exhaust Systems.