For 1990-2009 cars

Checks | Action
--- | ---
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 Important Preliminary Checks Before Starting in Symptoms .

• | Refer to Visual/Physical checks in Symptoms .

• | Search for bulletins.

• | Check the owners driving habits.

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

- | Are the tires at correct pressure?

- | Are there excessively heavy loads being carried?

- | Is acceleration too much or too often?

Fuel System |

• | Check the fuel pressure.

- | Refer to Fuel System Pressure Test (VIN K) .

- | Refer to Fuel System Pressure Test (VIN 1) .

• | Check the fuel injectors.

- | Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) .

- | Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F) .

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

• | Ensure each injector harness is connected to the correct injector/cylinder. Refer to Fuel Injector Electrical Harness Removal from Rail .

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

Sensor/System |

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

• | Check for proper calibration of speedometer. Connect J 33431-B (Signal Generator) to VSS electrical connector. Turn the ignition ON, tester ON and monitor the speedometer.

Ignition System |

• | Check for the proper ignition voltage output using the following steps:

- | Clip the spark tester J 26792 to engine ground.

- | Connect one end of a spark plug wire to the spark tester; leave the other end of the spark plug wire to the coil being tested.

- | Connect one end of another spark plug wire to the other coil tower; connect the other end of the spark plug wire to ground.

- | Crank the engine while observing the spark tester; a spark should be observed.

- | Repeat the above steps for each coil.

• | If spark is not present at the coil(s), check for the following conditions:

| Important:: If carbon tracking is detected on any component, replace that component and its mate.

- | Inspect the coil(s) for cracks, carbon tracking/arcing, or a resistance value outside the specified range.

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

- | Inspect the spark plug wires for signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, incorrect routing, or a resistance greater than the specified value.

VIN 1 Spark Plug Wires Resistance
3280 - 4921 ohms per meter (1000 ohms - 1500 ohms per foot)

VIN K Spark Plug Wires Resistance
3280 - 4921 ohms per meter (1000 ohms - 1500 ohms per foot)

| Important: Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition components will arc to ground when a secondary component is malfunctioning.

- | Check for a malfunctioning ignition control module.

- | Check the ignition system wiring for a loose ignition module feed, ground connection, or damaged system wiring.

• | Remove the spark plugs.

• | Inspect the spark plugs for the following conditions:

- | Check the spark plug(s) for fouling. Refer to Spark Plug Visual Diagnosis .

- | Check the spark plug for cracks.

- | Refer to Spark Plug Visual Diagnosis .

| Important:: If carbon tracking is detected on any component, replace that component and its mate.

- | Check the spark plugs for signs of carbon tracking on the porcelain or arching at the plug wire contact. Refer to Spark Plug Visual Diagnosis .

- | Check the spark plugs for incorrect gap. Refer to Spark Plug Visual Diagnosis .

- | Check the spark plugs for burned or damaged electrodes. Refer to Spark Plug Visual Diagnosis .

- | Check the spark plugs for incorrect heat range. Refer to Spark Plug Visual Diagnosis .

• | If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to Spark Plug Visual Diagnosis .

Engine Cooling System |

• | Check engine coolant level for being low.

• | Check for the incorrect or malfunctioning engine thermostat. Refer to Thermostat Diagnosis .

Engine Mechanical |

• | Check engine mechanical for the following:

- | Check the compression.

- | Check for sticking or leaking valves.

- | Inspect for worn camshaft lobe(s).

- | Check the valve timing.

- | Check for bent push rods.

- | Check for worn rocker arms.

- | Check for broken valve springs.

- | Check for excessive oil in combustion chamber - Leaking valve seals.

• | For incorrect basic engine parts, inspect for the following. Refer to Engine Overhaul .

- | Inspect the camshaft

- | Inspect the cylinder heads

- | Inspect the pistons, etc.

• | Refer to Engine Overhaul for diagnosis procedures.

Additional Checks |

• | Check TCC operation. Refer to Functional Test .

• | Check the exhaust system for a possible restriction.

- | Inspect the exhaust system for damaged or collapsed pipes.

- | Inspect the mufflers for heat distress or possible internal failure.

- | For possible plugged Three-Way catalytic converter. Refer to Restricted Exhaust System Check and/or Restricted Exhaust .