NO.14 POOR FUEL ECONOMY [L8, LF, L5]

id010346802000

14

POOR FUEL ECONOMY
DESCRIPTION
Fuel economy is unsatisfactory.
POSSIBLE CAUSE
•  Contaminated air cleaner element
•  Variable intake air control malfunction (LF, L5)
•  Engine cooling system malfunction
•  Improper ATF level (ATX)
•  Weak spark
•  Poor fuel quality
•  Erratic or no signal from CMP sensor
•  Clutch slippage (MTX)
•  Variable tumble control malfunction
•  Improper variable valve timing control system operation (LF, L5)
•  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
Warning
The following troubleshooting flow chart contains fuel system diagnosis and repair procedures. Read 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 SERVICE PRECAUTION" and “AFTER SERVICE PRECAUTION” described in this manual.
Caution
•  Disconnecting/connecting the quick release connector without cleaning it may cause damage to the fuel pipe and the 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 for the following:
•  Air cleaner element for contamination
•  ATF level (ATX)
•  Fuel quality
•  Coolant level
•  Brake dragging
•  Clutch slippage (MTX)
Are all the items normal?
Yes
Go to the next step.
No
Service if necessary.
Repeat Step 1.
2
Connect the M-MDS to the DLC-2.
Switch the ignition to ON (Engine off).
Retrieve any DTCs.
Are there any DTCs displayed?
Yes
DTC is displayed:
Go to the appropriate DTC inspection.
(See DTC TABLE [L8, LF, L5].)
No
No DTC is displayed:
Go to the next step.
3
Access the ECT PID.
Drive the vehicle while monitoring the PID.
(See PCM INSPECTION [L8, LF, L5].)
Is PID within specification?
Yes
Go to the next step.
No
Inspect for coolant leakage, and inspect the cooling fan and condenser fan operations or and inspect the thermostat operation.
4
Perform the spark test.
(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [L8, LF, L5].)
Is a strong blue spark visible at each cylinder?
Yes
Go to the next step.
No
Repair or replace the malfunctioning part according to the spark test result.
5
Inspect the fuel line pressure.
(See FUEL LINE PRESSURE INSPECTION [L8, LF, L5].)
Is the fuel line pressure correct?
Yes
Go to the next step.
No
Low:
Inspect the fuel pump relay and the fuel pump circuit.
Inspect the fuel line for clogging.
If there is no malfunction, replace the fuel pump unit
(See FUEL PUMP UNIT REMOVAL/INSTALLATION [L8, LF, L5].)
High:
Replace the fuel pump unit.
(See FUEL PUMP UNIT REMOVAL/INSTALLATION [L8, LF, L5].)
6
Inspect the variable tumble control operation.
(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [L8, LF, L5].)
Does the variable tumble control function properly?
Yes
Go to the next step. (LF, L5)
Go to Step 9. (L8)
No
Repair or replace the malfunctioning part.
7
Inspect the variable valve timing control system operation.
(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [L8, LF, L5].)
Does the variable valve timing control system function properly?
Yes
Go to the next step.
No
Repair or replace the malfunctioning part.
8
Inspect the variable intake air control operation.
(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [L8, LF, L5].)
Does the variable intake air control function properly?
Yes
Go to the next step.
No
Repair or replace the malfunctioning part.
9
Remove and shake the PCV valve.
Does the PCV valve rattle?
Yes
Go to the next step.
No
Replace the PCV valve.
(See POSITIVE CRANKCASE VENTILATION (PCV) VALVE REMOVAL/INSTALLATION [L8, LF, L5].)
10
Visually inspect the exhaust system parts.
Are there any deformed exhaust system parts?
Yes
Replace the suspected part.
No
Go to the next step.
11
Inspect the MAF sensor for contamination.
Is there any contamination?
Yes
Go to the next step.
No
Inspect for cause.
12
Inspect the MAF sensor for contamination.
Is there any contamination?
Yes
Replace the MAF/IAT sensor.
(See INTAKE-AIR SYSTEM REMOVAL/INSTALLATION [L8, LF, L5].)
No
Go to the next step.
13
Is the engine compression correct?
Yes
Inspect the valve timing.
No
Inspect for cause.
14
•  Verify test results.
―  If normal, return to the diagnostic index to service any additional symptoms.
―  If the malfunction remains, inspect the related Service Information and perform repair or diagnosis.
•  If the vehicle is repaired, troubleshooting is completed.
•  If the vehicle is not repaired or additional diagnostic information is not available, replace the PCM.