Checks
| Action
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DEFINITION: Fuel economy, as measured by an actual road test, is noticeably
lower than expected. Also, 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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• | Check the owners driving habits. |
- | Is the A/C ON or the Defroster mode ON full 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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• | Check that each injector harness is connected to the correct injector
and cylinder according to the firing order firing order: 1-8-7-2-6-5-4-3.
Relocate the injector harnesses as necessary. |
• | Check for foreign material accumulation in the throttle bore, coking
on the throttle valve, or on the throttle shaft. |
• | Check items that cause an engine to run rich long term fuel trim near -13 percent.
For a rich condition, refer to
DTC P0172 or P0175
. |
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Sensor/System
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• | Check the air intake system and crankcase for air leaks. |
• | Check the crankcase ventilation valve for proper operation. Place a
finger over the inlet hole in the valve end several times. The valve should
snap back. If not, replace the valve. |
• | Check for proper calibration of the speedometer. Connect J 33431-B
Signal Generator to the vehicle speed
sensor vehicle speed sensor (VSS) electrical connector. Turn ON the ignition
with the tester ON and monitor the speedometer. The speedometer
should indicate 86 km/h (54 mph). |
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Ignition System
|
• | Check for proper ignition voltage output with J 26792
Spark Tester . |
• | Remove the spark plugs and check for the following: |
• | An improper spark plug gap will cause a driveability problem. Gap the
spark plugs using a wire gauge gap tool. Refer to
Spark Plug Replacement
. |
• | Determine the cause of the fouling before replacing the spark plugs
if the spark plugs are gas, coolant, or oil fouled. Refer to one of the following
procedures: |
• | Visually and physically inspect the secondary ignition for the following: |
- | Ignition wires arcing to ground |
- | Ignition wires for proper routing |
• | Wetting down the secondary ignition system with water from a spray bottle
may help locate damaged or deteriorated components. Look and listen for
arcing or misfiring as you apply water. |
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Engine Cooling System
|
• | Check the engine coolant level for being low. Refer to
Loss of Coolant
in Engine Cooling. |
• | Check the engine thermostat for proper operation and for the correct
heat range. Refer to
Thermostat Diagnosis
in Engine Cooling. |
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Engine Mechanical
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• | Check the engine for the following mechanical conditions: |
- | Sticking or leaking valves |
• | Inspect the following components for incorrect basic engine parts: |
Refer to the appropriate procedures in Engine Mechanical 8.1L for diagnosis
procedures.
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Additional Checks
|
• | Visually and physically check the vacuum hoses for splits, kinks, and
proper connections and routing as shown on Vehicle Emission Control Information
label. |
• | Inspect the following components of the exhaust system for possible restrictions: |
- | The exhaust system for damaged or collapsed pipes |
- | The exhaust manifold for a collapsed inner wall |
- | The mufflers for heat distress or possible internal failure |
- | The three-way catalytic converters for possible plugged conditions--Compare
the exhaust system back pressure on each side of engine. Check back
pressure by removing secondary air injection (AIR) check valves near exhaust
manifolds. Refer to
Restricted Exhaust
in Engine Exhaust. |
• | Electromagnetic interference (EMI) on the reference circuit can cause
an engine miss condition. A scan tool can usually detect EMI by monitoring
the engine RPM. A sudden increase in RPM with little change
in actual engine RPM change indicates EMI is present.
Check for high voltage components, near ignition control circuits,
if a problem exists. |
• | Check the park neutral position (PNP) switch circuit. |
• | Check the intake and the exhaust manifold passages for casting flash. |
• | Check the brake system for dragging or improper operation. Refer to
Brake Caliper Inspection
in Brakes.
Ensure that the vehicle operator does not drive with a foot on the brake
pedal. |
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