Checks
| Action
|
DEFINITION: Fuel
economy, as measured by an actual road test is noticeably lower than expected.
|
Preliminary
|
| • | Search for service bulletins. |
| • | Inspect owners driving habits. |
| - | Is A/C ON full time, defroster mode ON? |
| - | Are tires at correct pressure? |
| - | Are excessively heavy loads being carried? |
| - | Is acceleration too much, too often? |
| - | Is E85 ethanol fuel used? If so, suggest the owner perform
an actual fuel mileage comparison using standard unleaded fuel. If the fuel
mileage is correct with standard unleaded fuel, the fuel consumption is normal. |
|
Fuel System
|
| • | Inspect items which can cause an engine to run rich--Short
term FT significantly in the negative range. Refer to Diagnostic Aids for
DTC P0172
. |
| • | Inspect items that can cause an engine to run lean--Short
term FT significantly in the positive range. Refer to Diagnostic Aids for
DTC P0171
. |
| • | Inspect for proper operation of the evaporative emission (EVAP)
control system. |
|
Sensor/System
|
| • | Inspect the oxygen sensor (O2S 1). The O2S 1 should
respond quickly to different throttle positions. If not, inspect the O2S 1
for silicon or other contaminants from fuel or the use of improper
RTV sealant. The sensors may have a white powdery coating. Silicon
contamination causes a high but false O2S 1 signal voltage--Rich
exhaust indication. The powertrain control module (PCM) will reduce
the amount of fuel delivered to the engine, causing a severe driveability
problem. |
| • | Inspect for proper operation of the manifold absolute pressure
(MAP) sensor. |
| • | Inspect for proper operation of the throttle position (TP) sensor. |
| • | Inspect for proper operation of the engine coolant temperature
(ECT) sensor. |
|
Ignition System
|
| • | Inspect for proper ignition voltage output with a J 26792
Spark Tester or equivalent. |
| • | Inspect the spark plugs for the following conditions: |
| - | Improper spark plug gap |
| - | Burned electrodes or heavy deposits |
| • | If the spark plugs are fuel or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. |
| • | Inspect the ignition control module (ICM) for proper ground connection. |
| • | Inspect the ignition coils for cracks or carbon tracking. |
| • | Inspect the spark plug wires for proper resistance and condition. |
|
Engine Cooling System
|
| • | Inspect engine coolant level for being low. Refer to
Loss of Coolant
in Engine Cooling. |
| • | Inspect for incorrect or malfunctioning engine thermostat. Refer
to
Thermostat Diagnosis
in Engine Cooling. |
|
Engine Mechanical
|
| • | Inspect engine mechanical for the following: |
| - | Sticking or leaking valves |
| - | Excessive oil in combustion chamber-Leaking valve seals |
| • | For incorrect basic engine parts. Inspect for the following: |
|
Additional Checks
|
| • | Inspect exhaust system for possible restriction. Inspect for the
following: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect mufflers for heat distress or possible internal failure. |
|
