A 2002 annual production Jetta avant-garde sedan, in the drive to accelerate the failure of failure. After receiving the car, first verify the phenomenon of failure, observed when the idle engine running a slight jitter, in situ air step on the gas, the work seems to be normal, no trouble. Then maintenance personnel to road test, slow step on the accelerator pedal, speed performance can also be. Accelerated, as the owner described, there is a crash phenomenon.
    According to the fault phenomenon, maintenance personnel with experience to judge, the fault area is in the oil. Engine no load state, the acceleration performance is acceptable, but the load state of the phenomenon of pacing, under normal circumstances, mostly mixed with too thin fault. What are the factors that affect the mixture too thin? The maintenance personnel first check the fuel pressure. If the fuel system is faulty, the pressure can not reach the standard value or can not increase with the throttle opening increases, reducing the fuel supply, will produce poor acceleration failure. Connected to the fuel pressure gauge, idle state, read the fuel pressure value of 260kPa, the needle is very smooth, acceleration up to 300kPa or so, indicating that the gasoline pump internal mechanical wear, gasoline pump and fuel pressure regulator work properly.
    Maintenance personnel analysis, this time if the engine from the electronic control system to read the fault code and observed from the data flow pulse width, oxygen sensor voltage, can be used as an important basis for judging the engine mixture is too thin. Connect the diagnostic instrument, read the fault code, the results show no fault code. Into the engine dynamic data flow test, the idle speed of 850r / min, the water temperature of 88 ℃, throttle opening of 6 °, the absolute pressure of 32kPa intake, fuel injection pulse width of 5.6ms, oxygen sensor signal voltage is 0 .3V or so. From the above data flow, we can see that there are several data anomalies. The throttle opening is 6 °, indicating that the throttle body dirty, the normal value is generally below 5 °; fuel injection pulse width 5.6ms, indicating that the idle state of the fuel injection is too large; oxygen sensor signal voltage 0.3V, then Indicating that the mixture is too thin. From the fuel injection pulse width and oxygen sensor signal voltage value analysis, it seems a bit contradictory. Why the fuel injection pulse width (that is, a long injection time), while the oxygen sensor voltage is low? Oxygen sensor signal voltage is low, said the mixture is too thin. From the theoretical analysis, fuel injection pulse width increases, will lead to increased fuel injection, mixed gas is too thick, oxygen sensor signal voltage should be greater than 0.45V or more. But the analysis of the phenomenon of failure, or mixed gas is too thin due. In order to verify whether the pulse width increases, or oxygen sensor "lie military intelligence", maintenance personnel unplug the vacuum tube on the intake manifold, brought a bottle of carburetor cleaning agent, the cleaning agent into the intake pipe, It is observed that the oxygen sensor signal voltage in the data stream rises rapidly to about 0.8V, and it is clear that the oxygen sensor can correctly reflect the concentration of the mixed gas.
    From this, the fault or the mixture is too thin caused. The engine ECU instructs the injection pulse width to increase, and the oxygen sensor signal voltage always shows that the mixture is too thin, and there must be no reason. What are the causes of the failure? If the vacuum sealing system leaks, it will also lead to the mixture is too thin, oxygen sensor that the signal, the feedback to the engine ECU, increase the fuel injection pulse width. As the oxygen sensor to correct the fuel injection has a certain range, more than the limit of correction, but also powerless. If the vacuum intake system a lot of leakage, to meet this situation. Then connected to the vacuum table, the vacuum table when the reading is 68kPa vacuum, indicating a smooth needle, it is clear that the vacuum sealing system without leakage failure.
    If the injector is dirty and clogged, it will also cause insufficient fuel injection. The oxygen sensor detects that the mixture is too thin and fed back to the engine control unit. Control unit to get this information, continue to increase the fuel injection pulse width, when the injector dirty clogging more serious, the mixture is extremely thin, more than the oxygen sensor adjustment range, it can not be amended fuel injection. Remove the four injectors, on the test bench and ultrasonic cleaning, and sure enough there are two injectors blocked more serious. Because the data flow shows the throttle opening is 6 °, indicating that there are dirty, the throttle body was cleaned. Then the maintenance personnel with the diagnostic device on the idle system for the adaptive value of the elimination and matching. Should be the owner of the requirements of the road test, anxious to step on the throttle, the conditions are accelerated performance are good, no trouble, the fault completely ruled out.