Mazda 626 Station Wagon, Workshop Manual

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TROUBLESHOOTING
NO.13 POOR FUEL ECONOMY
13 Poor fuel economy
DESCRIPTION • Fuel economy is unsatisfactory.
POSSIBLE
CAUSE
• Contaminated air cleaner element
• Engine cooling system malfunction
• Improper automatic transaxle fluid level
• Weak spark
• Poor fuel quality
• Erratic or no signal from CMP sensor
• Improper coolant level
• Inadequate fuel pressure
• Spark plug malfunction
• PCV valve malfunction
• Brake dragging
• Improper valve timing due to jumping out of timing belt
• Contaminated MAF sensor
• Improper engine compression
• Exhaust system clogging
Warning
• Following troubleshooting flow chart contains fuel system diagnosis and repair
procedures. Read following warnings before performing fuel system service:
— Fuel vapor is hazardous. It can easily ignite, causing serious injury and damage.
Always keep sparks and flames away from fuel.
— Fuel line spills and leakage are dangerous. Fuel can ignite and cause serious injuries
or death and damage. Fuel can also Irritate skin and eyes. To prevent this, always
complete “BEFORE REPAIR PROCEDURE” and “AFTER REPAIR PROCEDURE”. (See
Section F)
Caution
• Disconnecting/connecting the quick release connector without cleaning it may possibly
cause damage to the fuel pipe and quick release connector. Always clean the quick
release connector joint area before disconnecting/connecting, and make sure that It Is
free of foreign material.
Diagnostic Procedure
STEP INSPECTION RESULTS ACTION
1 Inspect following:
• Air cleaner element for contamination
• Automatic transaxle fluid level
• Fuel quality
• Coolant level
Are all items okay?
Yes Go to next step.
No Service as necessary.
Repeat Step 1.
2
Connect NGS tester to DLC.
Turn ignition switch on.
Retrieve any DTC.
Is “NO CODES RECEIVED/SYSTEM PASSED”
displayed?
Yes No DTC is displayed:
Go to next step.
No DTC is displayed:
Go to appropriate DTC test.
3 Connect NGS tester to DLC.
Access ECT PID.
Drive vehicle while monitoring PID.
(See F1-25 PCM INSPECTION (except for
GF4A-EL models))
(See Section F (for GF4A-EL models))
Yes Go to next step.
No
Inspect for coolant leakage, cooling fan and
condenser fan operations or thermostat
operation.
F1-129