NO.13 POOR FUEL ECONOMY [F2]

id010394850600

13

POOR FUEL ECONOMY
DESCRIPTION
Fuel economy is unsatisfactory.
POSSIBLE CAUSE
•  Contaminated air cleaner element
•  Engine cooling system malfunction
•  Improper automatic transmission fluid level
•  Weak spark
•  Poor fuel quality
•  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
•  The following troubleshooting flow chart contains the fuel system diagnosis and repair procedures. Read the following warnings before performing the fuel system services:
―  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 the “BEFORE SERVICE PRECAUTION” and “AFTER SERVICE PRECAUTION” described in this manual.

Diagnostic procedure

STEP

INSPECTION

RESULTS

ACTION
1
Inspect for following:
•  Air cleaner element for contamination
•  Automatic transmission fluid level
•  Fuel quality
•  Coolant level
Are all items normal?
Yes
Go to the next step.
No
Service if necessary.
Repeat Step 1.
2
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?
Yes
DTC is displayed:
•  Go to appropriate the DTC inspection.
No
No DTC is displayed:
•  Inspect instrument cluster operation.
3
Connect the M-MDS to the DLC-2.
Access ECT PID.
Drive vehicle while monitoring PID.
(See PCM INSPECTION [F2].)
Is PID within specification?
Yes
Go to the next step.
No
Inspect for coolant leakage, cooling fan operations or thermostat operation.
4
Is strong blue spark visible at each disconnected high-tension lead while cranking engine?
Yes
Inspect for following:
•  Spark plug malfunction
Repair or replace malfunctioning parts.
If normal, go to the next step.
No
Inspect for following:
•  High-tension leads
•  Ignition coil and connector
5
Install fuel pressure gauge between the fuel main pipe and the fuel distributor.
Start engine and idle it.
Measure fuel line pressure during idle.
Is fuel line pressure correct during idle?
(See FUEL PUMP UNIT INSPECTION [F2].)
Yes
Go to the next step.
No
Zero or low:
Inspect the fuel pump circuit.
Inspect for the open fuel pump relief valve.
Inspect for the fuel leakage inside pressure regulator.
Inspect for the clogged main fuel line.
High:
Inspect the pressure regulator for high pressure cause.
Inspect for the clogged fuel return line.
6
Remove and shake the PCV valve.
Does the PCV valve rattle?
Yes
Go to the next step.
No
Replace the PCV valve.
7
Is there restriction in exhaust system?
Yes
Inspect exhaust system.
No
Go to the next step.
8
Is brake system functioning properly?
Yes
Go to the next step.
No
Inspect for cause.
9
Inspect the MAF sensor for contamination.
Is there any contamination?
Yes
Replace the MAF sensor.
No
Go to the next step.
10
Is engine compression correct?
(See COMPRESSION INSPECTION [F2].)
Yes
Inspect valve timing.
(See TIMING BELT REMOVAL/INSTALLATION [F2].)
No
Inspect for cause.
11
•  Verify test results.
―  If normal, return to diagnostic index to service any additional symptoms.
―  If malfunction remains, inspect related Service Information and perform repair or diagnosis.
•  If vehicle is repaired, troubleshooting completed.
•  If vehicle is not repaired or additional diagnostic information is not available, replace the PCM.