For 1990-2009 cars

Inspections | Action
--- | ---
DEFINITION: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, fuel 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 Important Preliminary Inspections Before Starting in Symptoms - Engine Controls .

• | Search for bulletins.

• | Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views and Engine Controls Schematics .

• | Discuss driving habits with the owner.

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

- | Are the tires at the correct pressure?

- | Are the wheels and tires the correct size?

- | Are there excessively heavy loads being carried?

- | Is the acceleration rate too much, too often?

• | Remove the air filter element and inspect for dirt or for restrictions. Refer to Air Cleaner Element Replacement . Replace as necessary.

Fuel System |

• | Discuss with the owner the type, quality, and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Inspect the fuel injectors. Refer to Fuel Injector Diagnosis .

• | Test for incorrect fuel pressure. Refer to Fuel System Diagnosis .

• | Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Inspect that each fuel injector harness is connected to the correct injector and cylinder. Relocate the injector harnesses, as necessary.

Sensor/System |

• | Inspect for the following that may cause the engine to run rich:

Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section.

- | Any water intrusion in the heated oxygen sensor (HO2S) connector

- | The engine oil contaminated by fuel

- | Incorrect fuel pressure--Refer to Fuel System Diagnosis .

- | Any leaking fuel injectors--Refer to Fuel System Diagnosis .

- | Any vacuum hoses that are split, kinked, or improperly connected

- | An air intake duct that is collapsed or restricted

- | An air filter that is dirty or restricted--Refer to Air Cleaner Element Replacement .

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

• | Inspect for an engine coolant temperature (ECT) sensor that has shifted in value . Refer to Temperature Versus Resistance .

• | Inspect the crankcase ventilation system for proper operation. Refer to Crankcase Ventilation System Inspection/Diagnosis .

• | Inspect for an inaccurate speedometer. Refer to Symptoms - Displays and Gages .

Ignition System |

• | In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures:

- | Ignition System Specifications

- | Spark Plug Inspection

- | Spark Plug Replacement

• | Remove spark plugs and inspect for the following conditions:

- | Correct heat range

- | Wet plugs

- | Cracks

- | Wear

- | Improper gap

- | Burned electrodes

- | Heavy deposits

- | Verify that the spark plugs are of the correct type.

• | Inspect for proper ignition system output. Refer to Electronic Ignition (EI) System Diagnosis .

• | An improper spark plug gap will cause a driveability condition. Gap the spark plugs using a wire gage gap tool.

• | Determine the cause of the fouling before replacing the spark plugs.

• | Inspect for damaged or misaligned spark plug boots.

• | Inspect the electronic ignition (EI) module for proper ground connection.

• | Monitor the Misfire Current Counters while driving the vehicle in the conditions that the symptom occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 .

Engine Cooling System |

• | Inspect the engine coolant level for being low. Refer to Loss of Coolant .

• | Inspect the engine thermostat for proper operation and for the correct heat range. Refer to Thermostat Diagnosis .

Engine Mechanical |

• | Inspect engine mechanical for the following conditions:

- | Compression

- | Sticking or leaking valves

- | Worn camshaft lobes

- | Valve timing

- | Worn rocker arms

- | Broken valve springs

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

- | For more information, refer to one or more of the following procedures:

• | Engine Compression Test

• | Symptoms - Engine Mechanical

• | Oil Consumption Diagnosis

• | For incorrect basic engine parts, inspect the following components:

- | The camshaft--Refer to Camshaft Cleaning and Inspection .

- | The cylinder heads--Refer to Cylinder Head Cleaning and Inspection .

- | The pistons, etc.--Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection .

• | Refer to Symptoms - Engine Mechanical for diagnosis procedures.

Additional Inspections |

• | Visually and physically check the vacuum hoses for splits, kinks, and proper connections and routing as shown on Vehicle Emission Control Information label.

• | Inspect the transmission torque converter clutch (TCC) operation. The scan tool should indicate a RPM drop, when the system commands the TCC ON.

• | Inspect the exhaust system for a possible restriction. Inspect for the following conditions:

- | The exhaust system for damaged or collapsed pipes

- | The mufflers for heat distress or possible internal failure

- | The catalytic converters for being plugged--Refer to Restricted Exhaust .

• | Inspect the brake system for dragging or improper operation. Refer to Symptoms - Hydraulic Brakes . Verify that the vehicle operator does not drive with a foot on the brake pedal.