66f. The idle control valve is faulty;
g. The water temperature sensor is damaged;
h. The vacuum pressure sensor is damaged;
i. The air filter is blocked;
j. The injector leaks;
k. The compression pressure in the cylinder is too low;
l. The intake temperature sensor is damaged.
(3) Diagnosis and Troubleshooting
a. Check high pressure spark, check whether the high pressure spark on the ignition coil high pressure
bus and extension are OK, if the bus spark is week, replace the ignition coil, if the bus spark is OK
while the extension spark is too week, replace the ignition coil also; In addition, excessive spark
plug clearance will influence the starting feature, the clearance of the spark plug shall be adjusted
to normal value (0.8±0.1mm);
b. If there is low fuel pressure, check whether the battery voltage is OK, otherwise it shall be
troubleshot or replaced; check fuel pump check valve for leakage, check fuel filter and fuel pipe for
block, if there are leakage or block, replace or troubleshoot them;
c. If there is leakage for fuel pressure regulator, intake manifold is likely to be mixed with gasoline and
it is hard to start, troubleshoot or replace them;
d. Idle control valve can not be opened to maximum position due to mechanical wear, aging or control
circuit failure, the idle control valve shall be replaced and the control circuit failure shall be troubleshot;
e. If the water temperature sensor data is not accurate, it may cause small injection, check the water
temperature sensor based on the standard data and calibrate the data;
f. There is big time lag for intake pressure temperature sensor that makes it somewhat insensitive at
low speed and result in inaccurate injection, adjustment or replacement shall be made;
g. If the air cleaner filter is too dirty, the air flow resistance is excessively big, resulting in hard start,
as a result of it, the filter shall be replaced.
In a word, there are many factors causing the starting failure of the engine, analysis shall be made based on
the severe conditions of the faults. Generally speaking, check the ignition system first, then check intake
system, fuel system, control system, at last check the cylinder pressure, check the DTC before checking the
trouble. The diagnosis and troubleshooting procedures for starting failure of the engine are shown in (Figure
148).
67Figure 148II. Fuel pipeline and Circuit Fault for Hard Engine StartingHard engine starting indicates that starter can crank but fail to start the engine, or it may take multiple
consecutive starting efforts or long time rotation to successfully start the engine. For hard start fault, make
sure whether it occurs at cold or hot status or regardless of the cold or hot status.
1. Symptom
When starting, engine cranks at normal speed, but it takes longer to start or fails to start although cranks.
2. Causes:
a. Air cleaner is clogged;
b. Intake temperature sensor fault;
c. Water temperature sensor fault; Engine can not start
Check the starting system Repair or replace the part if it is faulty
Check the high voltage spark
No high voltage spark or weak spark OK
Check the ignition system Is there any sign of cranking
No sign of cranking There is sign of cranking
Check the electric fuel pump for operation Check the air cleaner filter
Operative Inoperative OK Clogged
Check the injector Check the electric fuel Check the Replaced
pump and its control circuit spark clearance
Operative Inoperative
Measure the fuel pressure
Measure the fuel pressure Check the injector
Measure the vapor pressure,
water temperature and intake
Excessively low OK Check the control circuit air temperature sensor
Check the fuel Check thecylinder pressure Check the cylinder pressure
pressure regulator
68d. Fuel pressure system abnormal;
e. Idle control valve fault;
f. Vacuum pressure sensor fault;
g. Ignition system fault;
h. The compression pressure in the cylinder is a little lower;
i. Injector leakage.
3. Diagnosis and Troubleshooting
a. Perform self-diagnosis first, check whether there is any DTC, if there is, find the reason and cause by the
DTC;
b.If it is hard for cold start but easy for hot start, check water temperature sensor and intake temperature
sensor for fault;
c. If the engine can not be started quickly in hot condition, the relief of the fuel pressure will be fast, then
repair and replacement shall be made;
d. If the spark is too weak, check high pressure coil, spark plug clearance and spark plug for carbon deposit,
repair or replace them one by one after isolating the problem;
e. Intake and exhaust valve is not completely closed, piston ring failure is likely to cause low compression
pressure in the cylinder, you should carefully repair intake & exhaust valve and seat, or replace them;
failed piston ring shall be replaced.
4. Diagnosis and Troubleshooting for hard starting and trouble shooting procedure. (Figure 149)III. Fuel Pipeline and Circuit Faults for Poor Engine OperationPoor engine operation includes: insufficient power, poor acceleration, poor deceleration, big fuel consumption,
rough idle and Engine overheat.
1. Insufficient Power
(1) Symptom:
Engine operation is normal without load but slow at load, insufficient power when uphill and not improved
even if the accelerator pedal is completely depressed, speed can not be increased and unable to reach the
maximum vehicle speed.
(2) Causes:
a. Air cleaner is clogged;
b. Poor intake system seal;
c. Intake pressure temperature sensor fault;
d. Low fuel pressure;
e. Broken pressure adjustor;
f. Clogged injector or poor atomization;
g. Throttle position sensor fault;
h. High pressure spark is too weak;
i. Improper valve clearance;
69j. Poor intake and exhaust valve seal, failed piston ring, low compression pressure;
h. Too many carbon deposit in spark plug and combustion chamber;
k. Water temperature switch and thermostat fault;
l. Aging of Oxygon sensor;
m. Incorrect ignition timing;
n. Check valve fault.
Figure 149Engine is difficult to start
Check whether the air cleaner is clogged Clogged
Troubleshooting
OK
Check the idle control valve NG
Repair or replace
OK
Check the fuel pressure Excessivly low
Service the electric fuel pump,
fuel filter and fuel pressure regulator
OK
Check the vacuum pressure sensor NG
Replace
OK
Check the water temperature sensor and intake air temperature sensor NG
Replace
OK
Check the start switch signal No
Service the start signal wire
OK
Check the ignition timing Misaligned
Adjust
OK
Check the cylinder pressure NG
Disassemble the engine
OK
Replace the ECU to retry
70(3) Diagnosis procedure for insufficient engine power (Figure 150)
2. Poor deceleration
(1) Symptom
Idling is normal, but the engine is frequently turned off upon sudden release of the accelerator pedal
during driving.
(2) Causes and Troubleshooting:
a. Throttle position sensor is damaged and shall be replaced;
b. Initial idling is not properly adjusted or automatic idle control is wrong, fuel cut RPM is too low,
ECU fault, repair or replace them.Insufficient power
Insufficient
Check whether throttle valve can be fully open Unable to be fully open
Adjust
OK
Check whether the air cleaner is clogged Clogged
Clean or replace
OK
Check the throttle valve position sensor for failure Abnormal
Repair or replace
OK
Check the water temperature switch and thermostat NG
Replace
OK
Check the vacuum pressure sensor for failure NG
Replace
OK
Check the fuel pressure Excessively low or high
Service the electric fuel pump,
fuel filter and fuel pressure regulator
OK
Check the oxygen sensor Incorrect
Replace
OK
Check the injector Incorrect
Replace
OK
Replace the spark plug, ignition coil and high voltage wire
OK
Disassemble the engineFigure 150
713. Poor acceleration
(1) Symptom
Engine speed can not be increased immediately after depressing the accelerator pedal, there is time lag,and the acceleration reaction is delayed or there is slight fluctuation during the acceleration.(2) Causes and Troubleshooting
a. There is fault in throttle position sensor, repair or replace it;
b. Poor intake system seal, repair it;
c. There is low fuel pressure, troubleshoot it;
d. Poor injector operation, clean or replace it;
e. Intake pressure temperature sensor fault, repair or replace it;
f. Check valve is damaged and shall be replaced;
g. Ignition advance angle is not correct and shall be adjusted;
h. Fuel pressure regulator is damaged and shall be replaced;
i. Air cleaner is clogged and shall be cleaned or replaced;
(3) Diagnosis procedure for poor acceleration (Figure 151)
Figure 151Poor acceleration
Check the air tightness of the intake air system Poor seal
Repair
OK
Check whether the air cleaner is clogged Clogged
Clean or replace
OK
Check the throttle valve position sensor for failure Abnormal
Repair or replace
OK
Check the fuel pressure Abnormal
Service the electric fuel pump,
fuel filter and fuel pressure regulator
OK
Check whether the injector inject properly
at idle and maximum load NG
Replace
OK
Check whether the check valve and EVAP are faulty Yes
Repair or replace
OK
Check whether the vacuum pressure sensor is OK NG
Replace
OK
Adjust a ECU to retry
724. Big fuel consumption
(1) Symptom:
Engine power is ok, but the fuel consumption is big, exhaust pipe discharges black smoke.
(2) Causes and Troubleshooting:
a. When idling, idle speed is high and shall be adjusted;
b. Water temperature sensor fault, service or replace it;
c. Water temperature switch and thermostat fault, repair or replace it;
d. Oxygen sensor fault, repair or replace it;
e. Fuel pressure is big and shall be adjusted;
f. Injector fault (fuel leakage), repair or replace it;
g. Throttle position sensor fault, repair or replace it;
h. Fuel pressure regulator is damaged and shall be replaced;
i. Intake pressure temperature sensor fault, repair or replace it.
5. Unstable idle, liable to be turned off
(1) Symptom:
Engine starts normally, but the idle is unstable regardless of cold or hot status, idle speed is too low and
the engine is liable to be turned off.
(2) Causes and Troubleshooting
a. Poor idle control valve operation, repair or replace it;
b. Low idle speed and faulty or improperly adjusted idle control valve, troubleshoot it;
c. Water temperature sensor fault, repair or replace it;
d. Poor intake system seal, need to be repaired;
e. High voltage spark is too weak, spark plug carbon deposit or electrode clearance is too small, need
to be repaired, cleared and adjusted;
f. Pressure sensor fault, repair or replace it;
g. The compression pressure in the cylinder is too low, need to be serviced;
h. Fuel line pressure is too low, needed to be serviced;
i. Air cleaner is clogged, clean or replace it;
j. Poor injector atomization, fuel leakage, block or big injection variation, need to be repaired;
(3) Diagnosis procedure (Figure 152)
6. Unstable idle at cold status, liable to be turned off
(1) Symptom
During the cold start, idle is unstable and engine is liable to be turned off, the normal idle is recovered
after warming of the engine.
(2) Causes and Troubleshooting
a. Water temperature sensor fault, repair or replace it;
b. idle control valve fault, repair or replace it.
737. Unstable idle or engine shut off at hot status
(1) Symptom
Idle speed is normal during the cold start and becomes unstable at hot status, idle speed is too
low or engine is shut off.
(2) Causes and Troubleshooting
a. Idle is adjusted too low, adjust it to normal condition;
b. Water temperature sensor fault, repair or replace it;
c. Poor injector operation or big injection variation, repair or replace it;
d. Poor water temperature switch and thermostat operation, repair or replace it;
e. Check valve is damaged and needs to be replaced.
Figure 152Rough ildling, easy for engine shut off
Check whethe the air tightness of the intake system is good Poor
Troubleshooting
OK
Check idle control valve for operation Inoperative
Disassemble or replace
Operative
Reset the initial idle speed
Check the spark plug Poor
Adjust the clearance or replace
OK
Check the fuel pressure NG
Check the electric pump, fuel
pressure regulator and fuel filter
OK
Check the injector NG
Replace
OK
Check the pressure sensor NG
Replace
OK
Check the cylinder compression pressure NG
Disassemble the engine
OK
Check and adjust the valve clearance