NO.11 POOR FUEL ECONOMY [WLT-1, WLT-2]

id010396913100

11
Poor fuel economy
DESCRIPTION
•  Fuel economy is unsatisfactory.
POSSIBLE CAUSE
•  Idle speed or idle-up speed incorrect adjustment
•  Accelerator cable free play incorrect adjustment
•  Air cleaner restriction
•  Engine cooing system malfunction
•  Improper coolant level
•  Improper engine compression
•  Exhaust system clogged
•  Injection timing incorrect
•  Injection nozzle malfunction
•  FIP malfunction
•  High idle-up speed
•  FICD malfunction
•  Fuel leakage
•  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
•  Inspect the idle speed and idle-up speed.
•  Is the idle speed and idle-up speed normal?
Yes
Go to the next step.
No
Go to symptom troubleshooting "NO.6 SLOW RETURN TO IDLE/FAST IDLE."
3
•  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.
4
•  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.
5
•  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
Clogged nozzle or seized needle valve:
•  Disassemble and clean or replace the injection nozzle.
Incorrect valve opening pressure:
•  Adjust injection nozzle opening pressure.
Malfunctioning nozzle gasket:
•  Replace nozzle gasket.
6
•  Is there restriction in the exhaust system?
Yes
Inspect the exhaust system.
No
Go to the next step.
7
•  Is the brake system functioning properly?
Yes
Go to the next step.
No
Inspect for the cause.
8
Note
•  The following test should be performed on vehicles with EGR system. Go to next step for vehicles without EGR system.
•  Perform the EGR system inspection.
•  Is the EGR system normal?
Yes
Go to the next step.
No
Repair or replace if necessary.
9
•  Measure the engine compression.
•  Is the compression normal?
Yes
Go to Step 11.
No
Go to the next step.
10
•  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.
11
•  Inspect the injection timing.
•  Is the injection timing normal?
Yes
Inspect the following:
•  FIP
No
Adjust the injection timing.
12
•  Verify the test results. If normal, return to the diagnostic index to service any additional symptoms.