Fault elimination method and steps

Vehicle fault elimination method (1). Method of target question closely Select the target by centering on systems related to trouble for fault phenomena and question closely based on examination. Select the target by centering on systems related to trouble for fault phenomena and question closely based on examination. (2). Screening method (Exclusion method) Eliminate the false and retain the true and remove the superficial phenomena by inquiring vehicle user and running up test to confirm fault authenticity; during the process of test run, analysis and judgment, systems (components) operated normally can be confirmed without fault one by one until assembly (components) causing faults are approached. Once the assemblies (components) causing faults are selected, then please repair or replace the assembly (components) and then inspect by test run. If fault phenomena are eliminated, the fault elimination work is finished. If fault phenomena are not eliminated, then please continue to carry out screening. (3). Principle judgment method Judge whether the selected target works normally according to the system or assembly (components) operating principle. (4). Running-up test method Please experience and feel the authenticity of fault phenomena, extent and range of problems through running-up test to establish target for eliminating vehicle faults. B. Vehicle fault elimination steps Step 1: Description of vehicle fault phenomena Under general conditions, when vehicles with faults are repaired, servicemen shall ask driver about vehicle fault phenomena, features, symptoms before fault appears and the time of fault and then make preliminary qualitative judgment. Step 2: Verification and test of vehicle fault phenomena (1). General steps are as follows: Before the vehicle is verified and tested, servicemen shall implement visual inspection on vehicle appearance and suspicious part around the vehicle. When visual inspection is implemented, please make sure: observe carefully and inspect with hands before disassembly and then inquiry continuously. At the same time, please inspect the vehicle by following the principle of from the easy to the difficult, from the near to the distant and from the outside to the inside. Please carry out test run and confirm “fault phenomena” and the systems incurring “fault phenomena”. Based on confirmation, please carry out experiment comparison for key parts. Step 3: Vehicle fault analysis Analysis can be divided into: please analyze the system (relevant assembly and component) which may cause “fault phenomena” and key parts (assembly) which may cause “fault phenomena”. The analysis shall be carried out according to vehicle system’s structure and operating principle. Please analyze repeatedly to find out causes. The analysis process is a complicated process so that it needs the support of theory, principle and experience and also needs meticulous and logical thinking. At the same time, experimental tests are continuously needed. As a result, reliable judgment conclusion can be obtained. Step 4: Vehicle fault judgment The vehicle fault judgment is made based on analysis and maintenance experience. The adjustment result may be correct or may be not correct, which is normal. The reason is that the fault may be simple and unique or may be multiple and comprehensive. Therefore, repeated analysis and experiment comparison are needed step by step until the problem is completely solved. Step 5: Vehicle fault elimination Vehicle fault elimination and repairing is not a complicated labor process. The main contents are simple disassembly and assembly. The disassembly shall follow the principle of from the easy to the difficult and from the outside to the inside to carry out partial disassembly to avoid disassembly with large area. Requirements for disassembly shall be noted when disassembly and assembly. Step 6: Verification and test after vehicle fault elimination The repaired vehicle shall be verified. The standard of verification and test is to eliminate vehicle fault phenomena and symptoms. If fault phenomena and symptoms are not eliminated, please repeat the above steps until vehicle fault is completely eliminated.

Engine cannot start

A. Fault possible cause and fault treatment (gas): (1). Gas cylinder has no gas or hand valve of gas cylinder is not open. Fault treatment: add gas or turn on hand valve of gas cylinder. (2). High pressure solenoid valve has no electricity or is damaged. Fault treatment: turn on the ignition key and then the solenoid valve has ringing “thump” sound. The connector clip of high pressure solenoid valve shall be plugged tightly. If the solenoid valve is damaged, please replace it. (3). Low pressure solenoid valve on FMV cannot be open or is not open fully. Fault treatment: inspect with notebook computer. After the ignition key is turned on, the gas pressure value is lower than 110PSIA. Please replace the solenoid valve or inspect valve plug. (4). Gas pressure is low. Fault treatment: inspect whether gas pipeline leaks gas. B. Fault possible cause and fault treatment (ignition circuit) : (1). Two relays of engine control module are damaged, therefore, please inspect whether three supply lines have electricity. Fault treatment: turn on the ignition key and inspect whether relay and fuse have 24V voltage with multimeter according to electrical diagrams. (2). Ignition module is damaged. Fault treatment: detect that the inanition coil misfires. Please inspect fault code, spark plug and high-tension cable. (3). Start-up rotary speed is too low (the lowest start-up rotary speed is 100r/min) Fault treatment: inspect whether the battery voltage can reach 24V. (4). Engine control module (ECM) is damaged. Fault treatment: replace ECM. C. Fault possible cause and fault treatment (air gas circuit and others): (1). Air intake is not sufficient Fault treatment: inspect whether air filter and air intake system are blocked and leaked. (2). Oxygen sensor connector clip is fused and short circuit is caused. Fault treatment: replace oxygen sensor. (3). Electronic throttle valve is damaged. Fault treatment: use software to test electronic throttle valve. If the electronic throttle valve is damaged, please replace it. (4). Intake valve and exhaust valve are adjusted wrongly. Fault treatment: inspect valve clearance according to instruction manual of diesel engine. (5). Some circuits on the finished vehicle have problems, such as neutral gear switch and etc. Fault treatment: inspect the circuits of the finished vehicle. (6). Velocity sensor fault. Fault treatment: use software to detect and then there is a fault code. Inspect the clearance between fluted disc and sensor. (7). The gear cup of signal generator turns and the angle of ignition advance changes greatly. At this moment, signal generator is fractured. Fault treatment: adjust the position of gear cup to make TDC scale mark aligning at central position inclining to the engine of speed sensor. Please carefully inspect whether the signal generator is fractured. If yes, please replace signal generator assembly.

Common faults elimination of steering system

A. Before fault maintenance is performed, it is advantageous to inspect and test to avoid wrong actions for maintenance. B. Inspect whether air pressure of steering wheel is enough, whether both sides are equal and whether wheels are worn. C. Inspect oil mass in oil tank is enough and whether is within the specified oil level. D. Inspect whether oil filter is clean and smooth E. Inspect whether flexible pipe is twisted, whether kinking is appropriate and is blocked. F. Inspect whether power-assisted steering oil pump belt slips. G. Inspect whether the following connections are obviously damaged or are not adjusted. (1). Joystick and universal joint; (2). Steering arm, draw bar, draw bar joint and universal joint; (3). Loosening situation of each steering connection.

Difficult to shift gear

When new user just uses heavy-duty truck with Fast gearbox, user usually reflects that it is not easy for vehicle to put into gear when starting. The reason is that user does not read instruction manual or is not trained so that user does not understand operating features of Fast gearbox. As we know the main box of old Fast gearbox has no synchronizer so that starting shift shall have clutch and the brake to coordinate the work. When the vehicle starts, if only the clutch pedal is stepped on but the switch valve of clutch and the brake is not turned on, and then the brake cannot work. Therefore, it is difficult to put into gear. Some users know the requirements for starting operation, but they still reflect that it is difficult to put into gear. Generally speaking, driver is too short and leg is too short, moreover, the seat is too high, therefore, the leg cannot touch the operational position of the brake when starting. As a result, the seat height shall be adjusted to meet the requirements. If the clutch really makes the brake switch valve turn on but it is still difficult to put into gear when starting. And it seems that the clutch is not released completely, and then it indicates that the clutch brake system has fault. Now please inspect braking gas circuit firstly, put the brake valve on the left lower of gear box, loosen the gas type fitting of brake cylinder and then step on the clutch pedal to turn on the clutch brake valve. Please observe whether gas type fitting exhausts gas to the outside. If it is not smooth to exhaust, then it indicates that there is fault for the switch valve of the brake. Please disassemble it or replace it. If it is normal to exhaust, and then it indicates that there is no problem in the switch valve and maybe the fault is on the brake cylinder. The treatment is to disassemble the clutch brake cylinder. Please observe whether the brake cylinder piston seal ring is wore or leaks gas, whether the piston can move smoothly and is not clamped. If it leaks gas, and then replace seal ring. Finally, please inspect whether the piston brake arc concave surface is worn seriously. If it is worn seriously, please replace the brake cylinder piston. Most importantly, many heavy-duty trucks are not equipped with “clutch braking device” for the moment. When the vehicle puts into gear when starting, the clutch pedal shall be stepped on and then put into gear later, which is the same with other types. If it is difficult to shift gear when the vehicle drives normally, then please inspect whether the reason is remote operation of shift level. Fast gearbox adopts remote shift mechanism on the heavy-duty trucks. If shift level is adjusted inappropriately or the jointing and bushing are too tight or excessively worn, the resistance of shift gear will be increased so that it is difficult to shift gear. In particular, some gears are difficult to shift. The screw can be adjusted by adjusting gear shift arm of gearbox to make joystick in appropriate position. For gearbox with double-lever double-shift mechanism, when lever of controlling selector lever or flexible shaft are not adjusted appropriately, the gear on the edge cannot put into reserve gear, creeper gear, and 7th and 8th gear. At this moment, please remove the operating lever or flexible shaft from the operating lever and then put the selector lever on the gear selection position of edge gears, adjust the length of operating lever or flexible shaft to reach the gear selection position of the limit and to connect joystick or flexible shaft with selector lever. At present, various series of gearboxes are equipped with all synchronizer. It is so convenient for these types of gearboxes to shift gear. When a gear is not easy to shift, please inspect whether the synchronizer of this gear is damaged. When gearbox with all synchronizer is operated, please shift gear with rational shift gear speed, which can reduce the abrasion of synchronizer and lengthen the service life of synchronizer. When shift gear is performed between two adjacent high gear and low gear (e.g. fourth and fifth gear), appropriate interval shall be needed for prodding high and low gears and pushing in gear. When the action of gear shift is too coherent, it is easy to burn and damage synchronizer of secondary gearbox. If remote operating lever is separated from gear shift arm of gearbox, it is still difficult to shift some gears with the method of directly operating gear shift arm, and it indicates that the inside of gearbox has fault. At this moment, repair with disassembly is needed. Generally speaking, the reason is that shift shaft of gearbox cover is deformed, sliding sleeve and two shafts are deformed or excessively worn or the shift shaft or lockpin of lifting level is loosened.

Brake drum is hot

The main cause for hot brake drum is that brake chamber does not return or return is too slow. Brake shoe and brake drum have no clearance, which can also make brake drum hot. Please inspect and adjust the clearance and inspect why the chamber does not return. When the brake chamber does not return, please inspect gas circuit and whether the brake camshaft is tight. When the return spring of brake shoe is broken, the brake drum is hot too. Please note that: the clearance between Steyr brake drum and tyre rim is too small, accuracy of manufacturing of domestic brake drum is low, the upper hot air path of the outer of brake drum is shallow, and therefore, heat dissipation is too poor. When the vehicle runs for a long distance downhill, the engine exhaust emission brake shall slow down and motor (foot) brake shall be used less possibly to avoid that the brake drum is too hot.

Brake cannot work

The brake cannot work and the effect is poor, which may caused by gas circuit system. Brake shoe’s friction plate and brake drum have problems. The touch area between brake shot plate and brake drum shall be larger than 70% of the total area. At the same time, the friction plate shall be clean, dry and have no greasy dirt and moist. In order to guarantee the touch surface between brake shoe’s friction plate and brake drum, when the brake drum is out of round and has drag mark and friction plate is damaged or the is replaced, please perform smooth turning on the surface of friction plate and brake drum with special tools. The practical experience shows that the effect of both end faces of brake shoe’s friction plate meshed is better than meshed center and unmeshed ends. Therefore, when brake friction plate performs smooth turning, the diameter of smooth turning shall be 0.2mm larger than inner diameter of brake drum. The maximum smooth turning amount of brake drum shall be 2mm on the diameter generally.

Battery energy is not enough

If the battery energy is not enough when igniting in the morning and it is difficult to pull the starter, a temporary method is: pour hot water on the battery, close all electric equipment and close the vehicle doors (the lower has foot lighting). After 5-10 minutes, the vehicle can start. Later please drive the vehicle to change the battery.

Gearbox overheating

The permissible working temperature of fast gearbox shall be no more than 120℃. Gearbox can generate certain heat because of friction of moving member. The normal working temperature is about 38℃ higher than the ambient temperature. The heat is dissipated through gearbox housing. If heat dissipation is not normal, overheating will be caused. It is normal that vehicle gearbox is “too hot to touch” when the vehicle runs in hot summer. But if the coat of paint of gearbox is cracked and high temperature appears, please pay attention to inspection. There are many causes for overheating of gearbox. Too much filled gear oil or serious oil starvation will cause overheating. The machine part is abnormally worn and the bearing is marched too tight, which also can result in overheating. Gearbox runs with low speed or high speed, which also can cause overheating. When the brand of gearbox gear oil especially the viscosity number is wrong, it is difficult to lubricate and then the gearbox is overheating. The air ventilator of gearbox can cause overheating and also can make gearbox seriously leaks oil on the input and output end. Engine exhaust system is too closed to gearbox. Running speed is less than 32Km/h generally. Working angle of gearbox shall be more than 12°.



Give Us A Shout
Get Email Updates
WhatsApp Online Chat !