Page 460 - Foton Workshop Manual - Auman EST-M

DI - 406 Diagnosis - Mechanical fault diagnosis
Mechanical fault diagnosis

Overview of mechanical fault diagnosis
Overview

Car fault means a car fully or partially loses its operation capacity, i.e. a part or component or their fit gets out
of order, e.g. the engine is hard to start or fails to start the car, the car leaks oil or water, the lighting system
fails. Common faults of car include sudden change of operating condition, sound abnormality, off odor, smoke
exhaust abnormality, temperature abnormality, appearance abnormality, abnormality of consumption of fuel
oil or lubricating oil, leakage, etc.
Reasons for fault

Normally mechanical faults of car include manmade fault and natural fault. A car may get out of order for any
of the following reasons:
1. Nonconforming car oil, e.g. fuel oil, lubricating oil, is used.

2. Inherent quality problems of car, e.g. bad material, insufficient strength or unsuitable design. Faults
caused by congential deficiency can be eliminated only by part or component replacement after they are found
in time during daily maintenance.
3. The driver doesn’t conduct maintenance or service or technical testing for the car on time.
4. Maintenance or repair doesn’t strictly execute the technicnal specification, and an accident potential is left
by test missing or violent operation.

5. The driver disobeys the driving specification, improperly loads or breaks the speed limit, or fails to
eliminate an abnormality on the way in time.
6. Natural wearing, corrosion, degradation and aging of kinematic pair. Faults caused by such reasons can be
not fully inhibited but mitigated only.
7. Bad running conditions (e.g. road, environment and weather). Faults caused by such reasons can be
prevented by relevant measure.

8. The driver is unskilled, has little driving or repair experience, or unfamiliar with the strucutre or
characteristics of car.

Failure phenomenon
1. Temperature abnormality

Temperature abnormality means the reading of water thermometer exceeds normal value (80℃~90℃) or
overheat is felt by finger touch. Usually overheat is shown by engine, gearbox assembly, drive axle assembly
or brake drum assembly. Normally such assemblies shall stay at certain temperautre no matter how long a car
runs. Besides engine, if unbearable heat is felt by finger touch to any such assembly, the component is
overheated and faulty. Usually engine overheat implies a fault of cooling system which may cause sudden
explosion, preignition, weak running even burnout of piston or other part or component if it’s not eliminated
in time; overheat of gearbox or drive axle may be caused by shortage of lubricating oil or improper tightness
of bearing, and gear, bearing and/or others may be damaged if the problem isn’t solved in time.
2. Off odor
Off odor means abnormal odor smelled by nose, e.g. rubber stink of short or burnt circuit; smoke odor of burn
of clutch friction lining or brake shoe upon brake lag, clutch skid or other fault during running; smog odor or
crude oil odor out of gas exhaust pipe, special odor of engine overheat or burn of engine oil or brake fluid,
etc. During driving, once burn-like rubber stink is smelled, the driver shall immediately park on the roadside,
find out the reason and eliminate the fault to prevent fire.

DI-406