GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Impala 🢒 Engine 🢒 Engine Controls - 3.4L 🢒 Poor Fuel Economy

Inspection/Test

Action

DEFINITION: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, current economy is noticeably lower than the economy was on this vehicle at one time, as previously shown by an actual road test.

Preliminary
    •  Refer to Intermittent Conditions before starting.
    •  Search for bulletins.
    •  Observe the owners driving habits.
       -  Is the 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 the fuel system circuits for proper operation. Refer to Fuel Pump Electrical Circuit Diagnosis .
    •  Test for low fuel pressure. Refer to Fuel System Diagnosis .
    •  Test for faulty fuel injectors. Refer to Fuel Injector Balance Test with Special Tool , Fuel Injector Balance Test with Tech 2 , Fuel Injector Solenoid Coil Test test procedures.
    •  Inspect for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    •  Ensure each injector harness is connected to the correct injector/cylinder.
    •  Inspect for fuel in the pressure regulator vacuum hose.

Sensor/System
    •  Observe the 24X crankshaft position (CKP) and camshaft position (CMP) sensors on scan tool. If both are not responding, check the sensor feed circuit. Both sensors use a common feed circuit.
    •  Inspect the air intake system and crankcase for air leaks.
         Inspect the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking, especially between the mass air flow (MAF) sensor and the throttle body.
    •  Inspect for proper calibration of speedometer. Connect J 33431-B Signal Generator to the vehicle speed sensor (VSS) electrical connector. Ignition ON, tester ON, and monitor the speedometer.

Ignition System
    •  Inspect for proper ignition voltage output using the following steps:
        1.  Attach the J 26792 Spark Tester to engine ground.
        2.  Connect the spark plug end of the spark plug wire to the J 26792 . Connect the other end of the spark plug wire to the coil being tested.
        3.  Connect the spark plug end of the companion spark plug wire to ground.

The companion spark plug wire is the wire attached to the corresponding coil tower.

        4.  Crank the engine while observing the J 26792 . A spark should be observed.
        5.  Repeat the above steps for each coil.
    •  If spark is not present at the coils, inspect for the following conditions:
       -  Coils--Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Resistance
5000-8000 ohms (5K-8K ohms)

       -  Spark Plug wires--Signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.

Spark Plug Wire Resistance
1 968 ohms per meter (600 ohms per foot).

    Important: :  Spraying the secondary ignition wires with a light mist of water may help locate an intermittent condition. Ignition voltage will arc to ground when a secondary component is faulty.

       -  Defective ignition module.
       -  Ignition system wiring--Loose ignition module feed or ground connection, or damaged system wiring.
    •  Remove spark plugs and inspect for the following conditions:
       -  Fouled plugs
       -  Cracks
       -  Wear
       -  Improper gap
       -  Burned or damaged electrodes
       -  Improper heat range or reach
    •  If the spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to Spark Plug Inspection .

Engine Cooling System
    •  Inspect the engine coolant level for correct level.
    •  Inspect for incorrect or faulty engine thermostat. Refer to Thermostat Diagnosis and Engine Fails To Reach Normal Operating Temperature in Engine Cooling.

Engine Mechanical
    •  Inspect the engine for the following conditions:
       -  Test the compression--Refer to Engine Compression Test in Engine Mechanical.
       -  Sticking or leaking valves
       -  Worn camshaft lobes
       -  Valve timing
       -  Bent push rods
       -  Worn rocker arms
       -  Broken valve springs
       -  Excess oil in the combustion chamber--Inspect for leaking valve seals.
       -  Low cylinder compression
    •  Inspect for incorrect engine parts, such as the following basic components:
       -  Camshaft
       -  Cylinder heads
       -  Pistons, etc.
    •  Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Additional
    •  Test the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis in Automatic Transaxle.
    •  Inspect exhaust system for possible restriction:
       -  Inspect exhaust system for damaged or collapsed pipes.
       -  Inspect mufflers for heat distress or possible internal failure.
       -  For possible plugged catalytic converter.