For 1990-2009 cars

Test/Inspection | Action
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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 Powertrain On Board Diagnostic (OBD) System Check .

• | Refer to Intermittent Conditions .

• | Search for bulletins.

• | Inquire about the owner's driving habits:

- | Is the A/C ON full time (Defroster mode ON)?

- | Are the tires inflated to the correct pressure?

- | Are excessively heavy loads being carried?

- | Is acceleration too much, too often?

Fuel System |

• | Test the fuel pressure. Refer to Fuel System Pressure Test .

• | Test the fuel injectors. Refer to Fuel Injector Balance Test , Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F) .

• | Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Verify that each injector harness is connected to the correct injector/cylinder. Refer to Engine Controls Schematics .

• | Inspect for fuel in the pressure regulator vacuum hose.

Sensor/System |

• | Test the air intake system and the crankcase for air leaks. Refer to Air Intake System Description and Crankcase Ventilation System Description .

• | Monitor the 24X Crankshaft Position and Camshaft Position Sensors on scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Test all 24X and CMP sensor circuits for intermittents. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

• | Monitor the 3X parameter on the scan tool. If the 3X is not responding, inspect the 7X CKP Sensor and circuits for intermittents. Inspect the IC circuit, Bypass circuit, 3X Reference High Circuit, and the 3X Reference Low circuit for intermittents. If these circuits become open, or shorted may not set a DTC immediately, but are capable of causing driveability complaints. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

• | Verify proper calibration of 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 spark tester; leave the other end of the spark plug wire connected 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 spark tester; 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
5000-8000ohms (5K-8Kohms)

- | 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
600ohms per foot (1 968ohms per meter).

| Important: : Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. 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 spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

Engine Cooling |

• | Inspect the engine coolant level for being low.

• | Inspect for an incorrect or faulty engine thermostat. Refer to Thermostat Diagnosis in Engine Cooling.

Engine Mechanical |

• | Inspect for the following engine mechanical concerns:

- | A low compression. Refer to Engine Compression Test in Engine Mechanical.

- | Sticking or leaking valves

- | Worn camshaft lobes

- | The valve timing

- | Bent push rods

- | Worn rocker arms

- | Broken valve springs

- | Excessive oil in the combustion chamber or leaking valve seals

• | Inspect for incorrect basic engine parts including the following:

• | The camshaft

• | The cylinder heads

• | The pistons, etc.

• | Refer to Engine Mechanical for diagnostic procedures.

Additional |

• | Test the torque converter clutch (TCC) operation.

• | 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.

- | Test for a or plugged catalytic converter. Refer to Restricted Exhaust System Check .