Page 77 of 392

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
Page 80 of 392

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
Page 82 of 392

7510. Engine overheat (Table 6)
Table 6Ite m Symptom Trouble shootingRepair or replace
Bad radiator hose Replace
Bad radiator tube strapSupplement welding, otherwise
replace it
Bad cylinder gasket Replace
Cracky cylinder blockRemedy with infiltration technology
or replace it
Poor water pump seal Replace the seal
Replace the anti-freeze liquid
Replace the thermostatBroken we ldSupplement weldingCorrosion result in pin holeFill the pinhole with clear coat,
otherwise replace it
Repair and dredge
Improve the ventilation
Repair or replace the water pump
Troubleshooting, replace the motor if
it is d a ma ge d
Replace
Repair and dredge
Repair or replace the oil pan if there
is o il le a k a ge , r e fill t he o il if it is no t
s up p le me nt e d in t imeCause
Ba d ra diator c over
Clogge d cooling tubePoor ventilationWater
le a ka ge
Anti-fre eze liquid not repla ce d
Bad thermostat
Radiator is
faultyWater
le a ka ge Insufficient
coolantF a ulty fa n vo lta ge
Disabled radiator temperature control
switch
Water jacket is clogged because of too much scale
I ns uffic ie nt e ngine o il ( o il le a k a ge o r d e la ye d filling)P oor
c ooling
Poor FanFaulty water pump
Page 83 of 392

7611. General engine fault symptom and faulty area (Table 7)
Table 7
Unable to explode initially
Unable to explode completely
Difficult for cold start
Difficult for hot start
No fast ilde
Low idle speed
High idle speed
Rough ildling
Idle hunting
At urgent acceleration
When the accelerator pedal is releasec
During idling
Poor acceleration
Hunting during driving
Insufficient power
KnockInta ke a bosolute pre ssure
se nsor
c c c c c c c c c
Water temperature sensor c c c c c c c c c c
Re volution spee d se nsor
c
Throttle valve position
se nsor
c c c c c c c c
Vehicle speed sensor
c
Fuel pump system
c c c c c c
Fue l pre ssure regulator
c c c c c c c c c c
Fue l filte r a nd pipe line
c c c c c c c
Injector
c c c c c c c c c
Sta rte r signal
c c
Ignition c oil
c c c
Spark plug
c c c c c c c c
High pre ssure ca ble
c c
Ignition timing
c c c c c c c
Igniter in the ECU
c c c c
Throttle valve
c c c c c
Throttle valve body c c c
Air leakage in the intake
air system c c c c c c c c
Air valve
c c c c c
ECU powe r supply circuit
c
Ignition swtich
c
Ma in re la y
c
Fuel pump re lay cPoor driving Difficult to start Poor idling Engine off
Power
supply
system Control
system
Fuel
system
Ignitio n
system
Intake
air
systemSuspect
AreaSymptom
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