There are many reasons for engine jitter. When a problem occurs in a certain system of the engine and causes the malfunction of starter jitter, this phenomenon alone immediately points out where the fault point is impossible, so for maintenance personnel, accurate troubleshooting should be completed, we have to start with the data system that the engine can give. The following is a brief summary of the causes of engine jitter and maintenance ideas (taking passat1.8 T as an example). If there is any inappropriate place, criticism and correction are welcome.
I. Engine jitter caused by ignition system
1) spark plug
The first problem faced by the car during cold start is low temperature. The temperature in the engine is not enough, and the temperature of fuel and lubricating oil is not enough. Therefore, more fuel should be injected during cold start to meet the requirements of power. The larger the gap of the spark plug, the smaller the ignition energy.
When the fuel atomization is not good at low temperature, the fuel needs higher ignition energy. When the car is used for a long time, the ignition gap of the spark plug will easily become larger, resulting in a decrease in ignition energy, the ignition gap and time control of spark plugs will be different, but ECU cannot diagnose this deviation and still treat "them" equally, which leads to practical and theoretical errors, as a result, the power generated by some cylinders is relatively small, which affects the power and makes the car shake.
2) ignition coil
Ignition coil is the energy source of spark generated by spark plug, and its working quality directly affects the quality of ignition and the completion of ignition. The ignition coil of passat1.8 T car is used directly with spark plug, which saves ignition wire connection in the middle.
ECU identifies the working condition and knock condition of the whole set of ignition through knock sensor. Maintenance personnel can communicate with ECU through special instruments to know the specific location of the failure. In the maintenance example, we often find that the air under the ignition coil cannot be excluded due to the failure to pay attention to the sealing condition of the ignition coil when installing the ignition coil, and the heating expansion of the gas causes the ignition coil to pop up, as a result, artificial engine jitter and so on are caused.
II. Jitter caused by oil supply system failure
1) nozzle
The blockage, leakage, and resistance of the fuel injection nozzle will affect the quality of the fuel injection. When one or more of them produce deviation, the oil-gas mixing ratio of each cylinder is not properly allocated, and the vibration caused by inconsistent power between the cylinder and the cylinder is generated. The maintenance of the fuel injection nozzle should be cleaned regularly to maintain a normal good atomization state. The basic parameters during inspection are a very important basis.
Check whether the fuel charge of the nozzle is even or not, and whether the atomization degree is good, which requires a dedicated laboratory table. It is not difficult to do these tasks, for maintenance personnel, it is the key to judge that the fault is on the nozzle. Usually, we can only see the injection time of the nozzle through data flow, but we cannot judge its quality. The general method is "oil cut-off method".
2) oil pump
Oil supply system components such as oil pump, fuel filter and oil pressure regulator are faulty, which causes oil pressure fluctuation and leads to unstable engine operation. Check this part mainly depends on the fuel pressure gauge, connect the oil pressure gauge to the distribution pipe, run the engine at idle speed, observe the pressure value of the gauge at this time, and make a preliminary judgment on the fuel system through the data.
After the injection time of the injector is determined, the fuel pressure directly affects the amount of fuel charge, which also affects the concentration of the mixture. There is also a pipe straight joint connection active carbon canister from the fuel tank. The carbon tank absorbs the fuel vapor in the fuel tank and controls it through the solenoid valve to send the fuel vapor to the intake pipe, which will also affect the concentration of the mixture, this is a place that repairmen often ignore.
III. Engine jitter caused by intake system
1) intake tube and valve if carbon deposits occur in the valves and intake ports of the engine, ECU determines that an error occurs because carbon deposits can absorb a proper amount of fuel. When the engine is shut down, there will always be some valves in the open state. Carbon deposit adheres to the working surface of the valves and cools after cure after one night or more,
When starting again, the pressure deviation between the cylinder and the cylinder is caused by lax valve closing, which makes it difficult to start the cold car or the engine jitter after starting. The characteristics of this fault are easier to understand, after the hot car, the failure phenomenon is not obvious or the phenomenon disappears. The way to deal with such faults is cleaning. No matter whether you prevent them in advance or clean them afterwards, the purpose is to keep the intake pipe unblocked and clean.
2) air filter \air flow meter \throttle gate \intake connection hose
Air filter the filter element is blocked due to long-term use, which makes the intake volume small, intake hose aging damage or leakage at each connection, air flow meter data deviation, throttle gate sensor damage, etc. All these factors will cause the ECU of the control unit to affect the operation of the mixture, resulting in engine jitter. Maintenance check this part of fault method form: ("look", "Listen", "Touch", "try" and so on. 3) worm gear supercharger parts
The failure of the free press often leads to weakness, resulting in idle jitter or acute loss of throttle engine jitter, which often occurs in the recirculation part, focusing on checking the recirculation pipeline, solenoid valve, sensor, circuit, etc.
IV. Jitter caused by mechanical parts of the engine
After the engine is used for a long time, the gap between each cylinder liner and the piston will also be different in size or small, that is, some gaps are large and some gaps are small. During cold start, there is no good oil lubrication, and cylinders with large clearance easily leak certain high temperature gas from the clearance, thus reducing power output. However, to solve mechanical problems, inspection and maintenance will take a lot of trouble, and some even need overhaul to solve the problems.
V. Jitter caused by water temperature sensor failure
Water temperature sensor is one of the important bases for computer to judge the working condition of the engine at that time. If the temperature of the engine is minus 10 degrees Celsius when it starts cold, but the sensor "tells" the computer "The current temperature is 20 degrees Celsius", then the computer will inject oil according to the working condition of 20 degrees Celsius, and the oil volume is of course small, of course, jitter is natural.
Conclusion
To sum up, we can see that there are three necessary factors to make the engine work normally: one is sufficient ignition energy, the other is mixed gas suitable for working conditions, third, sufficient cylinder pressure. These three are indispensable, otherwise the engine runs unstable, causing abnormal jitter of the engine. Then, once the engine has this kind of fault phenomenon, we should also start with this idea and gradually find out and eliminate the fault so as to make the engine work normally.
