NO.11 POOR FUEL ECONOMY [WL-3]

id0103b5913100

11
Poor fuel economy
DESCRIPTION
•  Fuel economy is unsatisfactory.
POSSIBLE CAUSE
•  Incorrect adjustment of idle speed
•  Accelerator pedal misadjustment
•  Air cleaner restriction
•  Engine cooling system malfunction
•  Poor fuel quality
•  Improper coolant level
•  Turbocharger malfunction
•  Improper engine compression
•  Exhaust system clogging
•  Injection timing is incorrect
•  Injection nozzle malfunction
•  Injection pump malfunction
•  Fuel leakage
•  Fuel inlet-filter restriction or clogging
•  Brake dragging
•  EGR system malfunction

Diagnostic procedure

STEP

INSPECTION

ACTION
1
•  Inspect for the following:
―  Fuel quality including water contamination
―  Air cleaner element restriction
•  Inspect the 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.
•  Turn the engine switch to the ON position (Engine off).
•  Retrieve any DTCs.
•  Is a DTC displayed?
Yes
DTC is displayed:
Go to the appropriate DTC test.
No
No DTC is displayed:
Go to the next step.
3
•  Access the ECT PID.
•  Drive the vehicle while monitoring the PID.
•  Is the PID within specification?
Yes
Go to the next step.
No
Inspect for coolant leakage, cooling fan operation or thermostat operation.
4
•  Inspect the idle speed.
•  Is the idle speed normal?
Yes
Go to the next step.
No
Go to symptom troubleshooting "NO.6 SLOW RETURN TO IDLE/FAST IDLE."
5
•  Perform the EGR system inspection.
•  Is the EGR system normal?
Yes
Go to the next step.
No
Inspect the following:
•  EGR solenoid (vent)
•  EGR solenoid (vacuum)
•  EGR valve
•  Vacuum hose connections
•  Wiring harness between EGR solenoids and PCM terminals
Repair or replace if necessary.
6
•  Inspect for fuel leakage from the fuel pipe.
•  Is any fuel leakage found on the fuel pipe?
Yes
Repair or replace if necessary.
No
Go to the next step.
7
•  Inspect the fuel-inlet filter for restriction and/or clogging.
•  Is the fuel-inlet filter normal?
Yes
Go to the next step.
No
Replace or cleanup the fuel-inlet filter.
Go to the next step.
8
•  Remove the injection nozzle.
•  Inspect the injection nozzle for the following:
―  Clogged nozzle
―  Seized needle valve
―  Incorrect valve opening pressure
―  Malfunctioning nozzle gasket
•  Is the injection nozzle normal?
Yes
Go to the next step.
No
Repair or replace the injection nozzle.
9
Note
•  The following test should be performed on vehicles with the turbocharger system.
•  Perform the turbocharger inspection.
•  Is the turbocharger normal?
Yes
Go to the next step.
No
Replace the turbocharger.
10
•  Is there restriction in the exhaust system?
Yes
Inspect the exhaust system.
No
Go to the next step.
11
•  Is the brake system functioning properly?
Yes
Go to the next step.
No
Inspect for the cause.
12
•  Measure the engine compression.
•  Is the compression normal?
Yes
Go to Step 14.
No
Go to the next step.
13
•  Inspect the timing belt for the following:
―  Chipping or gear teeth
―  Low tension
―  Breakage, damage or cracks
•  Is the timing belt normal?
Yes
Inspect for the following:
•  Burnt valve
•  Worn piston, piston ring or cylinder
•  Damaged cylinder head gasket
•  Damaged valve seat
•  Worn valve stem and valve guide
Repair or replace if necessary.
No
If the timing is incorrect, adjust the timing.
If the timing belt is not normal, replace the timing belt.
14
•  Inspect the injection timing.
•  Is the injection timing normal?
Yes
Inspect the following:
•  Boost sensor
•  Injection pump
No
Adjust the injection timing.
15
•  Verify the test results. If normal, return to the diagnostic index to service any additional symptoms.