Page 461 - Foton Workshop Manual - Auman EST-M

Diagnosis - Mechanical fault diagnosis DI - 407

3. Appearance abnormality IN

Once a car gets out of order, its apperance will change, too. Appearance abnormality such as horizontal or
vertical deflection may be found through inspection after the car is parked at a flat place. Appearance DI
abnormality is mainly caused by abnormality of car frame, car body, suspension device, tire and others,
furthermore, the car may take on unstable driving direction, off tracking, barycenter shift, tyre friction
EG
uneveness, etc.
4. Operation abnormality
TR
Operation abnormality means a car’s abnormity of start or running, i.e. sudden change of operating condition.
For example, the engine can hardly start again after sudden stalling; the engine is hard to start or operates
unstably after start; dynamic property lowers suddenly during running, and the car runs weakly thereupon; AX
during running, the brake fails or deflects suddenly, the steering wheel or fore wheel(s) sways even gets out
of control. The symptoms of operation abnormality are apparent and palpable, but they are formed from
FR
gradual change to sudden change for complex reasons, so a serious analysis must be done to judge whether
any doubtable symptom exists before sudden change, eliminate the false and retain the true, and locate the
ST
fault.
5. Smoke color abnormality
BR
Normal combustion products of a working engine mainly include carbon dioxide (CO 2) and some vapor. If the
engine oil burns abnormally, the waste gas will contain imperfectly combusted carbon particles, hydrocarbon,
carbonic oxide (CO) or much vapor, and turn black, blue or white, i.e. the smoke color is abnormal. To be BW
exact, the waste gas will turn blue if the engine oil upsurges to the cylinder, or black if the combustion is
imperfect, or white if the engine oil contains water.
EL
6. Oil consumption abnormality

Normally oil consumption abnormality means abnormality of consumption of fuel oil or lubricating oil, i.e.
consumption of fuel oil or lubricating oil exceeds relevant specified value. Such abnormality is also a fault
symptom. Usually increase of fuel oil consumption is caused by poor work of engine or improper adjustment
of the chassis’s drive system or brake system. Except for leakage, excessive engine oil consumption is usually
casued by engine fault. Such abnormality is usually accompannied by heavy or unstable smoke at the engine
oil port, abnormal smoke color and so on mainly because of overlarge fit clearance between piston and
cylinder wall or piston ring damage. Increase of enigne oil volume of a working engine may be caused by the
permeation of cooling water or gasoline to the oil pan. Hence abnormality of consumption of fuel oil or
lubricating oil is a main sign for poor operating condition of engine.
7. Sound abnormality

After start or on the way, a car sounds because of operation and vibration of parts and components. The
sounds of car include normal sound and abnormal sound. Normal sound means permissible light noise, e.g.
sound of friction between piston ring and cylinder wall inside the engine, sound of splash of engine oil, sound
of engine breakout and other permissible sounds during the running of car. Abnormal sound means abnoraml
sound of metal knock or other sounds that should not exist, e.g. sound of cylinder knock, sound of pin, sound
of bearing, sound of gas blow-by. Every kind of abnormal sound implies a fault that shall be eliminated
immediately. It’s noteworthy that multiple sound abnormalities can cause a serious mechanical accident and
must be seriously treated. In practice, heavy sound accompanied by apparent trembling implies a major fault,
and the driver shall immediately park on the roadside for troubleshooting. Abnormal sounds for different
reasons have different sound characteristics, e.g. the sound of cylinder knock for overlarge fit clearance
between piston and cylinder is “clank”, a clear and melodious sound of metal knock; the sound of pin for the

DI-407