NO.14 POOR FUEL ECONOMY

BHE010300103W16

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 manual.
(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.

Diagnostic procedure

STEP

INSPECTION

RESULTS

ACTION

1
Does the engine knock/ping/detonate?
Yes
Go to the symptom troubleshooting "No.13 Knocking/pinging/detonation-Acceleration/cruise".
No
Go to the next step.
2
Inspect for the following:
• Air cleaner element for contamination
• Air suction at intake-air system (between MAF sensor and intake ports)
• ATF level (AT)
• Fuel quality
• Coolant level
• Brake dragging
• Clutch slippage (MT)
• MAF sensor installation
• Tire pressure
Are all the items normal?
Yes
Go to the next step.
No
Service if necessary.
Repeat Step 2.
3
Connect the WDS or equivalent to the DLC-2.
Retrieve any continuous memory, KOEO and KOER DTCs.
Are there any DTCs displayed?
Yes

DTC is displayed:

Go to the applicable DTC inspection.
(See DTC TABLE.)
No

No DTC is displayed:

Go to the next step.
4
Access the ECT PID.
Drive vehicle while monitoring PID.
Is PID within specification?
Yes
Go to the next step.
No
Inspect for coolant leakage, cooling fan operation or thermostat operation.
5
Is a strong blue spark visible at each disconnected high-tension lead while cranking the engine?
Yes
Inspect for the following:
• Spark plugs malfunction
• The eccentric shaft position sensor is improperly installed.
• Pulse wheel damaged on eccentric shaft
• Open or short circuit on the eccentric shaft position sensor
• Open or short circuit between the eccentric shaft position sensor and PCM terminal 2U or 2X
Repair or replace the malfunctioning parts.
If normal, go to the next step.
No
Inspect for the following:
• High-tension leads
• Ignition coils and connectors
6
Perform the fuel pump speed control operation inspection.
Does the fuel pump speed control operate properly?
Yes
Go to the next step.
No
Repair or replace the malfunctioning parts, according to the fuel pump speed control operation inspection results.
7
Inspect the MAF sensor for contamination.
Is there any contamination?
Yes
Replace the MAF sensor.
No
Go to the next step.
8
Connect the WDS or equivalent to the DLC-2.
Access the MAF, O2S11, O2S12 and IAT PIDs.
Are the PIDs values normal?
Yes
Go to the next step.
No

If the MAF PID is not as specified:

Inspect the MAF sensor.

If the O2S11 PID is not as specified:

Inspect the front HO2S.

If the O2S12 PID is not as specified:

Inspect the rear HO2S.

If the IAT PID is not as specified:

Inspect the IAT sensor.
9
Inspect the knock sensor.
Is the knock sensor normal?
Yes
Go to the next step.
No
Replace the knock sensor.
10
Visually inspect the exhaust system part.
Is there any deformed exhaust system?
Yes
Replace the suspected part.
No
Go to the next step.
11
Install the fuel pressure gauge to the fuel line quick release connector.
Start the engine and run it at idle.
Measure the fuel line pressure at idle.
Is the fuel line pressure correct at idle?
Yes
Go to the next step.
No

Zero or low:

Inspect for clogged fuel line.
If normal, replace the fuel pump unit.

High:

Replace the fuel pump unit.
12
Inspect the fuel injectors for the following:
• Leakage
• Injection amount
Are the injectors normal?
Yes
Go to the next step.
No
Replace the fuel injector.
13
Note
• The following test is for the A/C equipped models. Go to the next step for the A/C non-equipped models.
Perform the A/C Cut-off Control inspection.
Does the A/C cut-off control operate properly?
Yes
Go to the next step.
No
Repair or replace the malfunctioning parts, according to the A/C cut-off control inspection result.
14
Inspect the engine compression.
Is it normal?
Yes
Inspect the eccentric shaft bypass valve.
(See Engine Workshop Manual.)
No
Go to the next step.
15
Perform the metering oil pump control inspection.
Does the metering oil pump control operate properly?
Yes
Go to the next step.
No
Repair or replace the malfunctioning part according to the inspection results.
After that or replace the engine.
(See Engine Workshop Manual.)
16
Check the engine oil condition.
Is the engine oil low viscosity and/or is there a gasoline odor?
Yes
Replace the engine oil.
Inspect the ECT sensor and the related wiring harnesses.
After that overhaul or replace the engine.
(See Engine Workshop Manual.)
No
Go to the next step.
17
Inspect the oil pressure.
Is the oil pressure within the specification?
Yes
Go to the next step.
No
Repair or replace the malfunctioning part according to the inspection results.
After that overhaul or replace the engine.
(See Engine Workshop Manual.)
18
Turn the ignition switch off.
Disconnect the fuel line quick release connector and install the fuel gauge to the fuel line.
Start the engine and run it at idle.
Measure the fuel line pressure at idle.
Is the fuel line pressure correct at idle?
Yes
Go to the next step.
No
Replace the fuel pump unit.
After that overhaul or replace the engine.
(See Engine Workshop Manual.)
19
Check the oil pipe between the metering oil pump and the metering oil nozzle.
Is there any air and/or clogging in the oil pipe?
Yes
Inspect and repair for leakage and/or clogging in the oil passage at engine.
After that overhaul or replace the engine.
(See Engine Workshop Manual.)
No
Overhaul or replace the engine.
(See Engine Workshop Manual.)
20
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 the repair or diagnosis.