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;
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.
