GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2000 🢒 Eldorado 🢒 Engine 🢒 Engine Controls - 4.6L 🢒 Poor Fuel Economy

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DEFINITION: Fuel economy, as measure 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 Important Preliminary Checks Before Starting in Symptoms .
    • Search for bulletins.
    • Check the owner's driving habits.
    • Check the following:
       - A/C operation
       - Correct tire pressures
       - Excessive vehicle weight loads
       - Excessive acceleration

Sensor/System
    • Check for an engine coolant temperature (ECT) sensor shifted in value. Refer to Temperature Versus Resistance .
    • Check the VSS system for proper operation. Refer to Automatic Transaxle.
    • Check the throttle body, TP sensor, and accelerator cables for proper operation.
    • Check the knock system (KS) for excessive spark retard.

Fuel System
    • Check the fuel pressure. Refer to Fuel System Pressure Test .
    • Check the fuel injectors. Refer to:
    • Check for fuel in the pressure regulator.
    • Check the minimum idle speed.
    • Check for items that cause the engine to run rich.

Ignition System
    • Check for proper IC circuit connections at each ignition module assembly.
    • Check for proper ignition voltage output using the J 26792 spark tester.
    • Check the ignition coils for cracks, or damage.
    • Check for a missing or damaged ignition module assembly grounding spring.

       Important: If the spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

    • Check the spark plugs for the following conditions:
       - Fouling
       - Cracks
       - Incorrect gap
       - Incorrect heat range or reach
       - Burned or damaged electrodes

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

Engine Mechanical
    • Check the following:
       - Engine compression, refer to Engine Compression Test in Engine Mechanical.
       - Sticking or leaking valves
       - Worn camshaft lobe(s)
       - Valve timing
       - Worn rocker arms
       - Broken or weak valve springs
       - Excessive oil; in the combustion chamber-leaking valve seals, refer to Oil Consumption Diagnosis in Engine Mechanical.
    • Check for incorrect basic engine parts. Inspect the following:
       - Camshafts
       - Cylinder heads
       - Pistons, etc.

Additional Checks
    • Check the exhaust system for possible restrictions.
    • Check the torque converter clutch for proper operation. Refer to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission in Automatic Transaxle.