N0.14 Poor Fuel Economy: Notes

WARNING: This page is about a different car, the 2005 Mazda RX-8. However, it is still accessible from the selected car via links, so may be relevant.

NO.14 DESCRIPTION AND POSSIBLE CAUSE

14	POOR FUEL ECONOMY
DESCRIPTION	The fuel economy is unsatisfactory.
POSSIBLE CAUSE	Contaminated air cleaner element Air suction at intake-air system (between MAF sensor and intake ports) Poor fuel quality Inadequate fuel pressure Pressure regulator (integrated in fuel pump unit) malfunction Fuel pump relay stuck closed Fuel leakage from fuel injector Restriction in exhaust system Erratic signal from eccentric shaft position sensor Improper MAF sensor installation Improper fuel injector control operation (abnormal signals from MAF, ECT, front/rear HO2S and IAT sensors to PCM) Knock sensor malfunction (abnormal signal to PCM) Contaminated MAF sensor Improper engine compression Engine internal malfunction Abnormal engine oil condition (viscosity, deterioration) Low oil pressure Excessive fuel pressure Metering oil pump malfunction Leakage or clogging in oil pipe Leakage or clogging in oil nozzle Eccentric shaft bypass valve malfunction (stuck open) Improper cooling fan control system operation Thermostat malfunction (stuck open) Improper engine coolant level Improper ignition timing Weak spark Spark plug malfunction Brake dragging Low tire pressure Clutch slippage (MT) Improper ATF level (AT) Improper A/C operation (A/C cut-off control does not operate) WARNING: The following troubleshooting flow chart contains fuel system diagnosis and repair procedures. Read the following warnings before servicing fuel system: 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" described in this article. (See BEFORE REPAIR PROCEDURE .) (See AFTER REPAIR PROCEDURE .) CAUTION: Disconnecting/connecting quick release connector without cleaning it may possibly cause damage to fuel pipe and quick release connector. Always clean quick release connector joint area before disconnecting/connecting, and make sure that it is free of foreign material.

POOR FUEL ECONOMY

DESCRIPTION

The fuel economy is unsatisfactory.

POSSIBLE CAUSE

Contaminated air cleaner element
Air suction at intake-air system (between MAF sensor and intake ports)
Poor fuel quality
Inadequate fuel pressure
Pressure regulator (integrated in fuel pump unit) malfunction
Fuel pump relay stuck closed
Fuel leakage from fuel injector
Restriction in exhaust system
Erratic signal from eccentric shaft position sensor
Improper MAF sensor installation
Improper fuel injector control operation (abnormal signals from MAF, ECT, front/rear HO2S and IAT sensors to PCM)
Knock sensor malfunction (abnormal signal to PCM)
Contaminated MAF sensor
Improper engine compression
- Engine internal malfunction
- Abnormal engine oil condition (viscosity, deterioration)
- Low oil pressure
- Excessive fuel pressure
- Metering oil pump malfunction
  - Leakage or clogging in oil pipe
  - Leakage or clogging in oil nozzle
Eccentric shaft bypass valve malfunction (stuck open)
Improper cooling fan control system operation
Thermostat malfunction (stuck open)
Improper engine coolant level
Improper ignition timing
Weak spark
Spark plug malfunction
Brake dragging
Low tire pressure
Clutch slippage (MT)
Improper ATF level (AT)
Improper A/C operation (A/C cut-off control does not operate)
WARNING:
The following troubleshooting flow chart contains fuel system diagnosis and repair procedures. Read the following warnings before servicing fuel system:
- 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" described in this article.
  (See BEFORE REPAIR PROCEDURE .)
  
  (See AFTER REPAIR PROCEDURE .)
CAUTION:
- Disconnecting/connecting quick release connector without cleaning it may possibly cause damage to fuel pipe and quick release connector. Always clean quick release connector joint area before disconnecting/connecting, and make sure that it is free of foreign material.