Checks
| Action
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DEFINITION: Fuel economy, as measured by an actual road
test is noticeably lower than expected. Also, 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
|
| • | Check 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? |
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Fuel System
|
| • | Test the fuel injectors. |
| • | Inspect for fuel in the pressure regulator vacuum hose. |
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Sensor/System
|
| • | Inspect the intake system and crankcase for air leaks. |
| • | Test for proper calibration of speedometer. Connect a J 33431-C
signal generator to VSS electrical
connector. Ignition ON, tester ON and monitor the speedometer. |
|
Ignition System
|
| • | Test for proper ignition voltage output using the following steps: |
| - | Clip the J 26792
spark tester to engine ground. |
| - | Connect one end of a spark plug wire to the spark tester, leave
the other end of the spark plug wire to the coil being tested. |
| - | Connect one end of another spark plug wire to the other coil tower,
connect the other end of the spark plug wire to ground. |
| - | Crank the engine while observing the spark tester, a spark should
be observed. |
| - | Repeat the above steps for each coil. |
| • | If adequate spark is not present at the coils, test for the following
conditions: |
| - | Coils - Cracks, carbon tracking/arcing, or a resistance value
outside the specified range. |
Coil Secondary Resistance
5000 - 8000 ohms (5K - 8K ohms) | - | Spark Plug wires - Signs of arcing/cross firing, cracks, carbon
tracking, plug boot damage, pinched, incorrect routing, or a resistance more
than the specified value. |
Spark Plug Wires Resistance
3280-4921 ohms/meter(1000-1500 ohm/ft).
| | Important: Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. Ignition components will arc to ground
when a secondary component is malfunctioning.
|
| - | Malfunctioning ignition control module |
| - | Ignition System Wiring - Loose ignition module feed or ground
connection, or damaged system wiring. |
| • | Remove spark plugs and inspect for the following conditions: |
| - | Burned or damaged electrodes |
| • | If spark plugs are gas or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. |
|
Engine Cooling System
|
| • | Test engine coolant level for a low condition. |
| • | Test for incorrect or malfunctioning engine thermostat. Refer
to
Engine Overheating
in Engine
Cooling. |
|
Engine Mechanical
|
| • | Test for the following: |
| - | Sticking or leaking valves |
| - | Excessive oil in combustion chamber-Leaking valve seals |
| • | For incorrect basic engine parts. Inspect for the following: |
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Additional Tests
|
| • | Test TCC operation. Refer to A Diagnostic Starting Point in 4L60E
Automatic Transmission. |
| • | Test the exhaust system for a possible restriction. |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect mufflers for heat distress or possible internal failure. |
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