For 1990-2009 cars

Inspection/Test | 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 , 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.

• | 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 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) .

• | Inspect for contaminated fuel. 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 |

• | 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.

• | Inspect the air intake system and crankcase for air leaks.

• | Inspect for proper calibration of speedometer. Connect J 33431-B signal generator to VSS electrical connector. Ignition ON, tester ON and monitor the speedometer.

Ignition System | If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
Engine Cooling System |

• | Inspect engine coolant level.

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

Engine Mechanical |

• | Inspect the engine mechanical for the following conditions:

- | Proper compression

- | Sticking or leaking valves

- | Worn camshaft lobes

- | Valve timing

- | Bent push rods

- | Worn rocker arms

- | Broken valve springs

- | Excessive oil in combustion chamber or leaking valve seals

- | Low cylinder compression

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

- | Camshaft

- | Cylinder heads

- | Pistons, etc.-- Refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Additional |

• | Test TCC operation. Refer to Torque Converter Diagnosis in Automatic Transaxle .

• | Inspect the exhaust system for possible restriction:

- | The exhaust system for damaged or collapsed pipes

- | The mufflers for heat distress or possible internal failure

- | The catalytic converter for possible plugged conditions-- Refer to Restricted Exhaust System Check and Exhaust Noise in Engine Exhaust.