Poor Fuel Economy

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. Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . Inspect the owner's driving habits. 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	Inspect 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 (without Special Tool and E85) or Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) . Inspect the fuel injectors. Refer to Fuel Injector Coil Test , Fuel Injector Balance Test with Special Tool , or Fuel Injector Balance Test with Tech 2 . Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool and E85) or Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) . Inspect that each fuel injector harness is connected to the correct injector and cylinder. Relocate the injector harnesses as necessary. Inspect for foreign material accumulation in the throttle bore, coking on the throttle valve, or on the throttle shaft. Inspect for the following that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the heated oxygen sensor (HO2S) connector Engine oil contaminated by fuel An evaporative emission (EVAP) canister purge condition Incorrect fuel pressure - Refer to Fuel System Diagnosis . Leaking fuel injectors - Refer to Fuel System Diagnosis . An inaccurate mass air flow (MAF) sensor Blockage on the inlet screen of the MAF sensor - Refer to Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor Replacement . Vacuum hoses that are split, kinked, or improperly connected An air intake duct that is collapsed or restricted - Refer to Air Cleaner Resonator Outlet Duct Replacement . An air filter that is dirty or restricted - Refer to Air Cleaner Element Replacement .
Sensor/System	Inspect the air intake system and crankcase for air leaks. Inspect the crankcase ventilation valve for proper operation. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical. Inspect for an inaccurate speedometer. Refer to Symptoms - Instrument Panel, Gages and Console in Instrument Panel, Gages, and Console. Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Knock Sensor (KS) System Description .
Ignition System	Inspect for proper ignition voltage output with the J 26792 Spark Tester. See Special Tools . Remove the spark plugs and inspect for the following: Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . An improper spark plug gap will cause a driveability problem. Refer to Spark Plug Inspection . Gap the spark plugs using a wire gage gap tool. Refer to Spark Plug Replacement . Determine the cause of the fouling before replacing the spark plugs. Refer to Spark Plug Inspection . Visually and physically inspect the secondary ignition for the following: Ignition wires arcing to ground Ignition wires for proper routing Soaking the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water. Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .
Engine Cooling System	Inspect the engine coolant level for being low. Refer to Loss of Coolant in Engine Cooling. Inspect the engine thermostat for proper operation and for the correct heat range. Refer to Thermostat Diagnosis in Engine Cooling.
Engine Mechanical	Inspect engine mechanical for the following: 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 Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical. For incorrect basic engine parts, inspect for the following: The camshaft - Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. The cylinder heads - Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. The pistons, etc. - Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical. Refer to Symptoms - Engine Mechanical in Engine Mechanical for diagnostic 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. Refer to Diagnostic System Check - Vehicle in Vehicle DTC Information. Inspect the exhaust system for a possible restriction. Inspect for the following: Inspect the exhaust system for damaged or collapsed pipes. Inspect the mufflers for heat distress or possible internal failure. Inspect for possible plugged catalytic converters. Refer to Restricted Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change indicates EMI is present. Inspect for high voltage components, near ignition control circuits, if a condition exists. Inspect the park neutral position (PNP) switch circuit. Refer to Park/Neutral Position Switch Adjustment in Automatic Transmission - 4L60-E. Inspect the intake and the exhaust manifold passages for casting flash. Inspect the brake system for dragging or improper operation. Refer to Brakes Drag in Hydraulic Brakes. Verify that the vehicle operator does not drive with a foot on the brake pedal.