Inspections
| Action
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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.
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Preliminary
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• | 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? |
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Fuel System
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• | Discuss with the owner the type, quality, and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy. |
• | Inspect that each fuel injector harness is connected to the correct injector and cylinder. Relocate the injector harnesses as necessary. |
• | Inspect for the following conditions that may cause the engine to run rich: |
Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section. - | Water intrusion in the heated oxygen sensor (HO2S) connector |
- | Engine oil contaminated by fuel |
- | An evaporative emission (EVAP) canister purge condition |
- | For proper operation of the mass air flow (MAF) sensor |
- | Blockage on the inlet screen of the MAF sensor |
- | Vacuum hoses that are split, kinked, or improperly connected |
- | An air intake duct that is collapsed or restricted |
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Sensor/System
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• | Inspect the air intake system and crankcase for air leaks. |
• | Verify that the engine coolant temperature (ECT) sensor is not shifted in value. Refer to
Temperature Versus Resistance
for resistance specifications. |
• | Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to
Scan Tool Data Definitions
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Ignition System
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• | Remove the spark plugs and inspect for the following conditions: |
• | Determine the cause of the fouling before replacing the spark plugs. |
• | 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. |
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Engine Cooling System
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• | 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. |
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Engine Mechanical
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• | Inspect engine mechanical for the following conditions: |
- | Sticking or leaking valves |
- | Excessive oil in combustion chamber--Leaking valve seals. |
- | For more information refer to one of the following procedures: |
• | For incorrect basic engine parts inspect for the following components: |
Refer to
Symptoms - Engine Mechanical
in Engine Mechanical for diagnostic procedures.
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Additional Inspections
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• | 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 |
- | 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. |
• | Verify that the vehicle operator does not drive with a foot on the brake pedal. |
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