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
|
• | Check the powertrain control module (PCM) grounds for being clean,
tight, and in the proper locations. Refer to
Engine Controls Schematics
. |
• | 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? |
|
Fuel System
|
• | 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. Refer to
Throttle Body Cleaning
. Also inspect
for throttle body tampering. |
• | Check items that cause an engine to run rich long term fuel trim
near -13 percent. For a rich condition, refer to
DTC P0132 or P0152
. |
|
Sensor/System
|
• | 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 (VSS) electrical connector. Turn ON the
ignition with the tester ON and monitor the speedometer.
The speedometer should indicate 86 km/h (54 mph). |
|
Ignition
System
|
• | Check for proper ignition voltage output with J 26792
Spark Tester . |
• | Remove the spark plugs and check for the following: |
Refer to
Spark Plug Inspection
.
• | Determine the cause of the fouling before replacing
the spark plugs if the spark plugs are gas, coolant, or oil
fouled. Refer to
DTC P0172 or P0175
for diagnosis of the rich condition. Refer to
Spark Plug Inspection
for diagnosis of coolant
or oil fouled spark plugs. |
• | 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. |
|
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. |
|
Engine Mechanical
|
• | Check engine mechanical for the following: |
- | Sticking or leaking valves |
- | Excessive oil in combustion chamber--Leaking valve seals.
Refer to
Oil Consumption Diagnosis
in Engine Mechanical 4.8L, 5.3L, 6.0L. |
• | For incorrect basic engine parts inspect for the following: |
|
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. |
• | Check the exhaust system for a possible restriction. Check for
the following: |
- | Inspect the exhaust system for damaged or collapsed pipes. |
- | Inspect the exhaust manifold for a collapsed inner wall. |
- | Inspect the mufflers for heat distress or possible internal failure. |
- | Inspect for possible plugged 3-way catalytic converters by comparing
the exhaust system back pressure on each side of the engine. Check
the back pressure by removing the secondary air injection
(AIR) check valves near the 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 intake and the exhaust manifold passages for casting
flash. |
• | Check the brake system for dragging or improper operation. Refer
to
Brake Caliper Inspection
in Disc Brakes. Ensure that the vehicle operator does not drive with
a foot on the brake pedal. |
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