NO.14 POOR FUEL ECONOMY [L8, LF]

id0103a0802000

14 | POOR FUEL ECONOMY
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DESCRIPTION | • Fuel economy is unsatisfactory.
POSSIBLE CAUSE | • Contaminated air cleaner element • Improper ATF level (AT) • Brake dragging • Clutch slippage (MT) • Improper coolant level • Poor fuel quality • Engine cooling system malfunction • Improper operation of A/C system • Spark plug malfunction • Inadequate fuel pressure • Improper operation of variable tumble control • Improper operation of variable intake air control • Variable intake-air control malfunction • Restriction in exhaust system • Contaminated MAF sensor • Improper operation of variable valve timing control system • Improper engine compression • PCV valve malfunction • Valve timing malfunction • PCM malfunction Warning The following troubleshooting flow chart contains fuel system diagnosis and repair procedures. Read following warnings before performing 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 “BEFORE SERVICE PRECAUTION” and “AFTER SERVICE PRECAUTION” described in this manual. (See BEFORE SERVICE PRECAUTION [L8, LF].) (See AFTER SERVICE PRECAUTION [L8, LF].) 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
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1 | Inspect the following: • Air cleaner element for contamination • ATF level (AT) • Brake dragging • Clutch slippage (MT) • Coolant level • Fuel quality Is there any malfunction? | Yes | Repair or replace the malfunctioning part according to the inspection results. Repeat Step 1.
No | Go to the next step.
2 | Connect the M-MDS to the DLC-2. Perform the KOEO/KOER self test and the DTC Reading Procedure. (See KOEO/KOER SELF TEST [L8, LF].) (See ON-BOARD DIAGNOSTIC TEST [L8, LF].) Are any DTCs present? | Yes | Go to the appropriate DTC inspection. (See DTC TABLE [L8, LF].)
No | Go to the next step.
3 | Connect the M-MDS to the DLC-2. Perform the PID/DATA Monitor and Record Procedure. (See ON-BOARD DIAGNOSTIC TEST [L8, LF].) Access and record the ECT PID while warm up the engine from it is cold. Note • ECT PID increase incline speed is slowly while engine coolant temperature approx. 80 °C {176 °F} because of thermostat begins to open. (The ECT PID climb gradient is moderated because the thermostat starts to open when the engine coolant temperature is 80 °C {176 °F} or more.) Does the ECT PID increase incline become properly? | Yes | Go to the next step.
No | Inspect the coolant leakage, cooling fan and thermostat operation. Repair or replace the malfunctioning part according to the inspection results.
4 | Note • Following test is for vehicle with A/C system. If the A/C system is not equipped, go to the next step. Turn off the A/C switch and fan switch. Does the A/C magnetic clutch engage? | Yes | Go to the symptom troubleshooting “NO.24 A/C IS ALWAYS ON OR A/C COMPRESSOR RUNS CONTINUOUSLY”. (See NO.24 A/C IS ALWAYS ON OR A/C COMPRESSOR RUNS CONTINUOUSLY [L8, LF].)
No | Go to the next step.
5 | Perform the Spark Test. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [L8, LF].) Is the strong blue spark visible at each cylinder? | Yes | Go to the next step.
No | Repair or replace the malfunctioning part according to the inspection results.
6 | Install fuel pressure gauge between the fuel pipe and the fuel distributor. Start the engine and idle it. Measure the fuel line pressure during idle. (See FUEL LINE PRESSURE INSPECTION [L8, LF].) Is fuel line pressure correct during idle? | Yes | Go to the next step.
No | Zero or low: • Inspect the fuel pump and fuel pump relay related circuit. • Inspect for clogged fuel line. • If there is no malfunction: ― Replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION [L8, LF].) • If there is a malfunction: ― Repair or replace the malfunctioning part according to the inspection results. High: • Replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION [L8, LF].)
7 | Perform the Variable Tumble Control Operation Inspection. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [L8, LF].) Does the variable tumble control normal? | Yes | Go to the next step.
No | Repair or replace the malfunctioning part according to the inspection results.
8 | Perform the Variable Intake Air Control Operation Inspection. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [L8, LF].) Does the variable intake-air control function properly? | Yes | Go to the next step.
No | Repair or replace the malfunctioning part according to the inspection results.
9 | Visually inspect the exhaust system part. Is there any deformed exhaust system part? | Yes | Repair or replace the malfunctioning part according to the inspection results.
No | Go to the next step.
10 | Inspect the MAF sensor. (See MASS AIR FLOW (MAF) SENSOR INSPECTION [L8, LF].) Is there any contamination? | Yes | Replace the MAF sensor. (See INTAKE-AIR SYSTEM REMOVAL/INSTALLATION [L8, LF].)
No | Go to the next step.
11 | Perform the Variable Valve Timing Control System Operation Inspection. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION [L8, LF].) Does the variable valve timing control system operate properly? | Yes | Go to the next step.
No | Repair or replace the malfunctioning part according to the inspection results.
12 | Perform the “COMPRESSION INSPECTION”. (See COMPRESSION INSPECTION [L8, LF].) Is the engine compression correct? | Yes | Go to the next step.
No | Inspect for cause.
13 | Inspect the PCV valve. (See POSITIVE CRANKCASE VENTILATION (PCV) VALVE INSPECTION [L8, LF].) Is there any malfunction? | Yes | Replace the PCV valve.
No | Inspect the valve timing. Repair or replace the malfunctioning part according to the inspection results.
14 | Verify test results. • If normal, return to diagnostic index to service any additional symptoms. (See ENGINE SYMPTOM TROUBLESHOOTING [L8, LF].) • If malfunction remains, inspect related Service information perform repair or diagnosis. ― If vehicle repaired, troubleshooting completed. ― If vehicle not repaired or additional diagnostic information not available, replace the PCM. (See PCM REMOVAL/INSTALLATION [L8, LF].)