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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• | Verify that the powertrain control module (PCM) grounds are clean, tight, and in the proper locations. |
• | Inspect the owners driving habits. |
- | Is the A/C ON or the Defroster mode ON full time? |
- | Are the tires at the correct pressure? |
- | 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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• | 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: |
Notice: Refer to Heated Oxygen and Oxygen Sensor Notice in the Preface section. - | Water intrusion in the HO2S connector |
- | Engine oil contaminated by fuel |
- | An EVAP canister purge condition |
- | An inaccurate mass air flow (MAF) sensor |
- | Vacuum hoses that are split, kinked, or improperly connected |
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Sensor/System
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• | Inspect the air intake system and crankcase for air leaks. |
• | Inspect the crankcase ventilation valve for proper operation. Place a finger over the inlet hole in the valve end several times. The valve should snap back. If not, replace the valve. |
• | Inspect for an inaccurate speedometer. |
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Ignition System
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• | Inspect for proper ignition voltage output with the J 26792
Spark Tester . |
• | Remove the spark plugs and inspect for the following: |
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. |
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Engine
Cooling System
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• | Inspect the engine coolant level for being low. |
• | Inspect the engine thermostat for proper operation and for the correct heat range. |
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Engine Mechanical
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• | Inspect engine mechanical for the following: |
- | Sticking or leaking valves |
• | For incorrect basic engine parts inspect for the following: |
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: |
- | Inspect the exhaust system for damaged or collapsed pipes. |
- | Inspect the mufflers for heat distress or possible internal failure. |
- | Inspect for possible plugged three-way catalytic converters by comparing the exhaust system back pressure on each side of the engine. Inspect the back pressure by removing the secondary air injection (AIR) check valves near the exhaust manifolds. |
• | 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. |
• | Inspect the intake and the exhaust manifold passages for casting flash. |
• | Inspect the brake system for dragging or improper operation. Verify that the vehicle operator does not drive with a foot on the brake pedal. |
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