Page 462 - Foton Workshop Manual - Auman EST-M

DI - 408 Diagnosis - Mechanical fault diagnosis

loose fit between piston pin and connecting rod lining or piston pin hole is “patter”, a shrill and melodious
sound of knock similar to steel ball collision; the sound of connecting rod bearing for abrasion and loosening
of bearing and journal is “rattle”, a continous and and melodious sound of metal knock; sound of crankshaft
bearing for its loose fit with journal is “rub-a-dub”, a continuous and melodious sound of metal knock; sound
of gas blow-by for poor cylinder sealing is “chirp”. Hence a abnormal sound shall be carefully listened to for
correct distinguishing and quick troubleshooting.
8. Instrument abnormality

Various instruments on vehicle (ammeter, engine oil pressure gauge, water temperature gauge and barometer,
etc.) are used to indicate the working condition of appropriate vehicle part. In case of any abnormal indicated
reading, his shows the occurrence of vehicle fault. At this time, it is necessary to immediately park the vehicle
at appropriate place for troubleshooting.
9. Performance abnormality

Each use performance of a vehicle will reduce with the increasing mileage. However, such reduction is slow
that cannot often be found. If the use performance of a vehicle is found with sudden reduction during running,
this shows the occurrence of fault (such as rapid power drop, sudden serious front sway, brake failure, etc.). At
this time, it is necessary to immediately park the vehicle for troubleshooting.
10. Clearance abnormality

Each clearance has its standard value. Too large or small clearance shows the occurrence of fault. The
adjustment shall be done accordingly.
11. Leakage phenomenon

Leakage means the leakage of fuel, lubricating oil (engine oil, gear oil), coolant, brake fluid (or compressed
air) and power steering oil. This fault symptom is obvious that can be found directly. Leakage can result in
overheating, steering or brake failure, increased oil consumption and other faults as well as pollution against
machine part and environment, so any leakage shall be eliminated immediately if found.
Fault diagnosis method

Fault diagnosis means an analysis, determination and checking process to find out fault cause and position.
Currently, there are two vehicle fault diagnosis methods: One is artificial diagnosis method, and the other one
is instrument diagnosis method.
1. Instrument diagnosis method
Instrument diagnosis method is to use instrument and equipment to acquire the vehicle performance and fault
information without dismantling the vehicle assembly and to give the diagnosis conclusion of technical
performance and fault by comparing with the normal technical condition of vehicle. With the application of
electronic information and computer technology to vehicle, the diagnosis instrument and equipment of vehicle
fault is increasingly improved that more and more advanced instruments are applied to vehicle fault diagnosis.
The instrument and equipment can conduct fault diagnosis in a rapid and accurate manner and can find out
any latent. Also, it can anticipate the service life of assembly component.
2. Artificial diagnosis method

Artificial diagnosis method means qualitative diagnosis which is done by inspector to determine the technical
performance and fault of a vehicle based on his/her practical experience and observation and by using simple
tools and asking, seeing, hearing, touching and smelling, when the vehicle is not dismantled or is partially
dismantled. The specific practices are as follows:

a. Seeing: see the vehicle to find out any oil, water, gas and electricity leakage point, to confirm the working

DI-408