Checks
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DEFINITION: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the current fuel economy is noticeably lower than the vehicle's previous fuel economy, as shown by an actual road test.
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Preliminary Checks
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| • | Inspect the air filter for proper type and for dirt or restriction. |
| • | Inspect the vacuum hoses for leaks, restrictions and proper connections as shown on the vehicle emission control information (VECI) label. |
| • | Review the vehicle operators driving habits for the following items: |
| - | The A/C compressor clutch being engaged all the time |
| - | Excessive idling or stop and go driving |
| - | Low compressed natural gas (CNG) refill pressure--Check fill station pressure. |
| - | Excessively heavy loads being carried |
| - | Too much acceleration, too often |
Advise vehicle operator to fill the fuel tank and recheck fuel economy.
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Fuel System Checks
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| • | Inspect for fuel system leakage. |
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Sensor Checks
| Test the engine coolant temperature (ECT) sensor for proper operation by performing the following:
- Allow the engine temperature to reach ambient air temperature by leaving the engine OFF for several hours, overnight for most accurate results.
- Turn the ignition ON while leaving the engine OFF.
- Using a scan tool compare the ECT and intake air temperature (IAT) sensors displayed temperature.
The sensors should be within 3°C (5°F) of each other.
- Replace the ECT sensor or repair the ECT sensor circuit if the ECT is not near the expected value.
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Ignition System Checks
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| • | Remove and inspect the spark plugs for the following conditions: |
| • | Test for an open ignition control (IC) circuit. |
| • | Inspect the spark plug wires for the following: |
| - | Proper connections and routing |
| | Important:: More timing advance is required to operate the vehicle on CNG than on gasoline.
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| • | Test for proper operation of the Knock Sensor system. |
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