Checks
| Action
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DEFINITION: Fuel economy, as measured by an actual road test, is noticeably
lower than expected. Also, the fuel economy is noticeably lower than it 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 engine control module (ECM) grounds are clean, tight,
and in the correct locations. |
• | Inspect the following owner's driving habits. |
- | Is the A/C or the Defroster mode ON all the time? |
- | Are the tires at the correct pressure? |
- | Is there excessively heavy loads being carried? |
- | Is the acceleration rate too much, too often? |
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Fuel System
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• | Verify that the fuel injector harness is connected to the correct injector/cylinder
according to the firing order. |
• | Inspect for foreign material accumulation in the throttle bore, and for
carbon deposits on the throttle plate and shaft. Also inspect for throttle body tampering. |
• | Test or inspect items that can cause an engine to run rich. For a rich
condition, refer to
DTC P0172
. |
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Sensor/System
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• | Inspect the air intake system and the crankcase for air leaks. |
• | Test the crankcase ventilation valve. Place a finger over the inlet hole
in the valve end several times. The valve should snap back. If not, replace the valve. |
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Ignition System
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• | Remove the spark plugs and inspect for the following conditions: |
- | Refer to the following procedures: |
• | If the spark plugs are fouled by gas, coolant, or oil, determine the cause
before replacing the plugs. Refer to the following procedures. |
- | For diagnosis of a rich condition, refer to
DTC P0172
. |
• | Wetting down the secondary ignition system with water from a spray bottle
may help locate damaged or deteriorated components. Look/listen for arcing or misfiring
as the water is applied. |
• | Inspect for the correct installation of the ignition coil. Incorrect installation
may allow water to enter the spark plug area. Inspect for moisture and corrosion. |
• | Inspect the ignition coil and the spark plug boots for cracks or carbon
tracking. |
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Engine Cooling System
|
• | Test the engine thermostat. Verify that the thermostat is of the correct
heat range. Refer to
Thermostat Diagnosis
in
Engine Cooling. |
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Engine Mechanical
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• | Inspect for the following engine mechanical conditions: |
- | Excessive oil in the combustion chamber and for leaking valve seals |
- | Incorrect cylinder compression |
- | Sticking or leaking valves |
- | Excessive carbon buildup in the combustion chambers. Clean the chambers
with top engine cleaner. Follow the instructions on the can. |
- | For more
information, refer to the following procedures in Engine Mechanical - 0.8L (LBF): |
• | Inspect the following for incorrect basic engine parts: |
- | The pistons, connecting rods, and bearings |
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Additional Checks
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• | Inspect the vacuum hoses for splits or kinks. Verify that the connections
and routing are correct. |
• | Inspect the following exhaust system components: |
- | The exhaust system for physical damage |
- | The mufflers for heat distress or possible internal failure |
- | The three-way catalytic converter(s) for restrictions. |
• | Electromagnetic interference (EMI) on the reference circuit can cause
a misfire condition. You can usually detect EMI with a scan tool by monitoring the
engine speed. A sudden increase of the engine speed parameter with little change in
actual engine speed indicates that EMI is present. Inspect the high voltage components
near the ignition control circuit if a problem exists. |
• | Inspect the brake system for dragging or improper operation. Ensure that
the vehicle operator does not drive with a foot on the brake pedal. |
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