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. |
| • | 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
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| • | 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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