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
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| • | Refer to
Symptoms , Important Preliminary Checks Before Starting.
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| • | Check PCM grounds for being clean, tight and in the proper locations.
Refer to PCM wiring diagrams in Electrical Diagnosis.
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| • | 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
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| • | Check for incorrect minimum idle speed. Using a scan tool, monitor
IAC position. IAC should be between 5 and 50 counts. |
| • | Check each injector harness is connected to the correct injector/cylinder
according to the firing order (firing order: 1-8-4-3-6-5-7-2).
Relocate injector harnesses as necessary. |
| • | Check for injectors that are shorted internally. Compare injector
resistance. Injector resistance should be within one ohm of each other. Refer
to
Fuel Injector Solenoid Coil Test
. |
| • | Check for foreign material accumulation in the throttle bore,
coking on the throttle valve or on the throttle shaft. Also inspect for throttle
body tampering. |
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Sensor/System
| Check Air intake system and
crankcase for air leaks.
| • | Check Crankcase ventilation valve for proper operation. Place
finger over inlet hole in valve end several times. Valve should snap back.
If not, replace valve. |
| • | Check for proper calibration of speedometer. Connect J 33431-B
(Signal Generator) to VSS electrical connector. Ignition ON, tester ON and
monitor the speedometer. The speedometer should indicate 86 km/h (54 mph).
Refer to 8A (Cell 33)
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| • | Using a Scan Tool, monitor TP sensor voltage. The TP sensor voltage
should be less then 0.9 volt. If the TP sensor voltage is greater than 0.9
volt, inspect the ASR/TCS adjuster assembly (If so equipped). Also inspect
throttle body and accelerator cables for binding. Refer to Adjuster Assembly Throttle And Cruise Control Cables.
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Ignition System
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| • | Check for proper ignition voltage output with spark tester J 26792.
Refer to Distributor Ignition System for procedure. |
| • | Remove spark plugs and check for the following: |
| • | An improper spark plug gap will cause a driveability problem.
Refer to spark plug gap specification is Section OB. The spark plug gapping
should be done using a wire gauge gap tool (J 41319). Refer to Spark Plug Replacement.
If spark plugs are gas or oil fouled, the cause
of the fouling must be determined before replacing the spark plugs. Refer
to
DTC P0172 Fuel Trim System Rich Bank 1
and
DTC P0175 Fuel Trim System Rich Bank 2
to determine the Rich condition or Engine Mechanical
for the oil fouling condition. |
| • | Visually/Physically inspect Secondary ignition for the following: |
| - | Ignition wires for cross firing. |
| - | Ignition wires arcing to ground. |
| - | Ignition wires for proper routing. |
| - | Distributor cap for cracks or carbon tracking. |
| • | Wetting down the secondary ignition system with water from a spray
bottle may help locate damaged or deteriorated components. Look/listen for
arcing or misfiring as water is applied. |
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Engine Cooling System
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| • | Check engine coolant level for being low. Refer to Engine Cooling.
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| • | Check engine thermostat for having a faulty part or for wrong
heat range. Refer to Engine Cooling.
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Engine Mechanical
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| • | Check engine mechanical for the following: |
| - | Sticking or leaking valves. |
| - | Excessive oil in combustion chamber-Leaking valve seals. |
| - | Low cylinder compression. |
| • | For incorrect basic engine parts. Inspect for the following: |
Refer to Engine Mechanical
for diagnosis procedures.
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Additional
Checks
|
| • | Visually (physically) check: Vacuum hoses for splits, kinks, and
proper connections and routing as shown on Vehicle Emission Control Information
label. |
| • | Check TCC operation. Using a scan tool should indicate an RPM
drop, when the TCC is commanded ON. Refer to Transmission
Control Systems.
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| • | Check exhaust system for possible restriction. Check for the following: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect mufflers for heat distress or possible internal failure. |
| - | For possible plugged Three-Way catalytic converters by comparing
exhaust system back pressure on each side of engine. Check back pressure by
removing AIR check valves near exhaust manifolds. Refer to
Restricted Exhaust System Check
. |
| • | An engine miss condition can be caused by Electromagnetic Interference
(EMI) on the reference circuit. EMI can usually be detected by monitoring
engine RPM with a scan tool. A sudden increase in RPM with little change in
actual engine RPM change, indicates EMI is present. If a problem exists, check
routing of secondary ignition wires, high voltage components (Near Ignition
Control circuits). Check distributor ground circuit for being open or loose. |
| • | Check the Traction Control Adjuster Assembly for being out of
adjustment? Refer to Adjuster Assembly-Throttle And
Cruise Control Cables.
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| • | Check PNP switch circuit . Refer to
Park/Neutral Position Switch Check
, or use the Tech 1 and be sure the
scan tool indicates vehicle is in drive with gear selector in drive or overdrive. |
| • | Check for faulty motor mounts. Refer to Engine
Mechanical
for inspection of mounts. |
| • | Check for intake and exhaust manifold passages for casting flash.
Refer to Engine Mechanical.
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