Jetta SDI diesel cars using Bosch's VP37 electronically controlled axial piston pump, by the engine electronic control unit ECU according to the signal sent by each sensor, the logic operation, issued a final execution command, control VP37 axial piston Type fuel injection start time and fuel injection, so that it meets the engine starting, idle, small load, medium load, heavy load, full load and acceleration and other needs of the situation.
    Maintenance personnel received a Jetta SDI diesel car repair, the car configuration AQM engine idle operation is unstable, the process of acceleration and weakness, and the phenomenon of mild smoke. Jetta diesel cars can cause the cause of idling instability, generally caused by the following aspects:
    (1) the cylinder pressure of individual cylinders is too low.
    (2) VP37 axial piston pump is damaged, resulting in uneven fuel supply.
    (3) individual cylinder injectors are damaged or clogged.
    We first tested the cylinder pressure, the cylinder pressure in the standard range (2500 ~ 3100kPa) within. Excluding the cylinder pressure problem, the fault point is concentrated on the VP37 pump and the injector. With V. A. G1551 for testing, test results: ① no fault in the memory. ② diesel fuel injection rate of 2.0mg / s or so changes, a larger range of change. ③ The fueling time starts at 94. ④ data group 013 value as shown in the table.
    According to the above data, we first adjust the fuel injection starting angle 04 function under the 000 group, 2 area value of 50 to 60, the fault is still the phenomenon. And then check the fuel system, the results did not find water or impurities, oil flow. Check the circuit system everything is normal. So the VP pump is suspected to have failed, replace a new, the fault is still the same. We re-start to analyze the idle speed control data group 013, why 3-cylinder work better than the other three tanks, and beyond the adjustment of the allowable range (± 1.9mg / s), which means that the three-cylinder oil too too much. So remove the 3-cylinder injector to test its opening pressure, the result is the pressure reaches 7000kPa when the injector began to inject. The standard opening pressure is 19000 ~ 20000kPa, which means that the 3-cylinder injector does not meet the standard pressure in advance to open, replace the 3-cylinder injector, troubleshooting. We found a spring break in the 3-cylinder injector.
    After the repair of this failure analysis, Jetta SDI diesel car fuel injector is the use of double coil spring control injector opening pressure, due to 3 cylinder injector 1 spring break, resulting in open pressure is too low, the injector open Prematurely, too much fuel injection, needle valve lift sensor to the signal back to the engine computer. Needle valve lift sensor to the engine control unit to accurately reflect the fuel injection start time, fuel injection time that fuel injection, but also play a role in the cylinder. At this time the engine control unit control VP pump to reduce fuel injection, that is, according to the needle valve lift sensor signal, 3 cylinder fuel injection is sufficient. And to 1, 2 and 4 cylinder, the opening pressure is high to 19000 ~ 20000kPa, this time will lead to 1,2 and 4 cylinder fuel supply, lack of capacity. At this point the engine computer in order to maintain the idling operation is stable, there will be a large range of changes in fuel supply to maintain the engine idling operation, to the maintenance staff intuitive feeling is the diesel pump has been damaged. Therefore, Jetta AQM engine in the maintenance process, if found that the fuel injection is too large or too small, it is not necessarily VP axial piston pump distribution damage, be sure to do a thorough and comprehensive inspection.