NO.14 POOR FUEL ECONOMY [MZI-3.7]
id0103d2802000
14 |
POOR FUEL ECONOMY |
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DESCRIPTION
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Fuel economy is unsatisfactory.
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POSSIBLE CAUSE
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• Contaminated air cleaner element
• Engine cooling system malfunction
• Improper ATF level
• Weak spark
• Poor fuel quality
• Erratic or no signal from CMP sensor
• Improper variable valve timing control system operation
• Improper coolant level
• Inadequate fuel pressure
• Spark plug malfunction
• PCV valve malfunction
• Brake dragging
• Improper valve timing due to jumping out of timing chain
• Contaminated MAF sensor
• Improper engine compression
• Exhaust system clogging
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Diagnostic procedure
STEP |
INSPECTION |
RESULTS |
ACTION |
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1
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Inspect for the following:
• Air cleaner element for contamination
• ATF level
• Fuel quality
• Coolant level
• Brake dragging
Are all items normal?
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Yes
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Go to the next step.
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No
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Service if necessary.
Repeat Step 1.
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2
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Connect the M-MDS to the DLC-2.
Turn the ignition switch to the ON position (Engine off).
Retrieve any DTCs.
Are there any DTCs displayed?
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Yes
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DTC is displayed:
Go to the appropriate DTC inspection.
(See DTC TABLE [MZI-3.7].)
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No
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No DTC is displayed:
Go to the next step.
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3
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Access ECT PID.
Drive vehicle while monitoring PID.
(See PCM INSPECTION [MZI-3.7].)
Is PID within specification?
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Yes
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Go to the next step.
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No
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Inspect for coolant leakage, cooling fan and condenser fan operations or thermostat operation.
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4
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Perform the spark test.
Is strong blue spark visible at each cylinder?
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Yes
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Go to the next step.
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No
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Repair or replace the malfunctioning part according to spark test result.
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5
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Install the fuel pressure gauge between the fuel pipe and the fuel distributor.
Start the engine and idle it.
Measure fuel line pressure during idle.
Is fuel line pressure correct during idle?
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Yes
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Go to the next step.
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No
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Low:
Inspect the fuel pump relay and fuel pump circuit.
Inspect the fuel line for clogging.
If there is no malfunction, replace the fuel pump unit
High:
Replace the fuel pump unit.
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6
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Inspect for variable valve timing control system operation.
Does the variable valve timing control system function properly?
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Yes
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Go to the next step.
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No
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Repair or replace the malfunctioning part.
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7
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Remove and shake the PCV valve.
Does the PCV valve rattle?
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Yes
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Go to the next step.
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No
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Replace the PCV valve.
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8
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Visually inspect the exhaust system part.
Is there any deformed exhaust system?
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Yes
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Replace the suspected part.
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No
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Go to the next step.
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9
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Inspect for contaminated MAF sensor.
Is there any contamination?
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Yes
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Go to the next step.
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No
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Inspect for cause.
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10
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Inspect the MAF sensor for contamination.
Is there any contamination?
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Yes
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Replace MAF sensor.
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No
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Go to the next step.
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11
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Is engine compression correct?
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Yes
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Inspect the valve timing.
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No
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Inspect for cause.
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12
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• Verify test results.
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