Inspection/Test
| Action
|
DEFINITION: Fuel economy, as measured by an actual road test is noticeably lower
than expected. Also, the economy is noticeably lower than the economy was on this
vehicle at one time, as previously shown by an actual road test.
|
Preliminary
|
| • | Observe the owner's driving habits. |
| - | Is the A/C ON full time, defroster mode ON? |
| - | Are tires at correct pressure? |
| - | Are tires and wheels the correct size? |
| - | Are excessively heavy loads being carried? |
| - | Is acceleration too much, too often? |
|
Fuel System
|
| • | Ensure that each injector harness is connected to the correct injector/cylinder. |
| • | Inspect for fuel in the pressure regulator vacuum hose. |
|
Sensor/System
|
| • | Observe the 24X crank sensor and the camshaft position (CMP) sensor signal
present parameters on the scan tool. If both are not responding, inspect the sensor
feed circuit. Both sensors use a common feed circuit. |
| • | Inspect the air intake system and crankcase for air leaks. |
| | Inspect the air intake ducts for being collapsed, damaged areas, looseness, improper
installation, or leaking, especially between the mass air flow (MAF) sensor and
the throttle body. |
|
Ignition System
|
| • | Inspect for proper ignition voltage output using the following steps: |
| 1. | Attach the J 26792
Spark
Tester to engine ground. |
| 2. | Connect the spark plug end of the spark plug wire to the J 26792
. Connect the other end of the spark plug wire
to the coil being tested. |
| 3. | Connect the spark plug end of the companion spark plug wire to ground.
The companion spark plug wire is the wire attached to the corresponding coil tower. |
| 4. | Crank the engine while observing the J 26792
. A spark should be observed. |
| 5. | Repeat the above steps for each coil. |
| • | If spark is not present at the coils, inspect for the following conditions: |
| - | Coils--Cracks, carbon tracking/arcing, or a resistance value outside
the specified range. |
Coil Resistance
5,000-8,000 ohms | - | Spark plug wires--signs of arcing, cross firing, cracks, carbon
tracking, plug boot damage, pinched, improper routing, or a resistance value outside
the specified range. |
Spark Plug Wire Resistance
3,000 ohms per foot
(9,842 ohms per meter).
| | Important: : Spraying the secondary ignition wires
with a light mist of water may help locate an intermittent problem. Ignition voltage
arcs to ground when a secondary component is faulty.
|
| - | Defective ignition 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 |
| - | Improper heat range or reach |
| • | If spark plugs are gas or oil fouled, the cause of the fouling must be
determined before replacing the spark plugs. Refer to
Spark Plug Inspection
. |
|
Engine Cooling System
|
| • | Inspect the engine coolant level for correct level. |
| • | Inspect for incorrect or faulty engine thermostat. Refer to
Thermostat Diagnosis
in Engine Cooling. |
|
Engine Mechanical
|
| • | Inspect the engine for the following conditions: |
| - | Sticking or leaking valves |
| - | Excessive oil in combustion chamber--Leaking valve seals |
| • | Inspect for incorrect engine parts, such as the following basic components: |
|
Additional
|
| • | Test torque converter clutch (TCC) operation. |
| • | Inspect exhaust system for possible restriction: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect mufflers for heat distress or possible internal failure. |
| - | For possible plugged catalytic converter |
|
