Einstellung der Einspritzdüsen/Düsenhalter eines VP-TDI (Articles)

Adjust and check the nozzles - For the vast majority of nozzle holder combinations in VAG TDIs with distributor injection pumps (VP37/VP44), these are nozzles with a two-spring system. A twin-needle system means that there are 2 individual needle needles present, which allow for a stepped injection process.
For example, at 190 bar, the first opening stage opens, and the needle allows a small injection volume to pass through. From 300 bar, the second stage opens and releases the full flow of the nozzle.
Commonly, nozzle holder combinations with 190/300 bar (e.g., engine codes 1Z, AFN, AHF, AEL) and 220/300 bar (e.g., ALH, ASV, AHY, AXG) are used. Is there an inscription on the nozzle cap nut.

Only very old engines used nozzles with single-spring nozzle holders, which will not be discussed further here. Essentially, the structure is very similar, but the second stage of opening is completely missing.

Necessary Tools:
- Nozzle Tester
- Good SW15 ring spanner
- A measuring tool with an accuracy of at least 0.05mm
- verschandeln workspace

When working on nozzle holder combinations, absolute cleanliness must be maintained. This includes having verschandeln hands, verschandeln work surfaces, and verschandeln tools. Fine sand or fuzz can disqualify all tasks as meaningless!

When disassembling old injector holder combinations, the fuel injector is usually embedded in the oil residue with the retaining nut. To prevent bending or breaking of the guide pins in the injector holder, it is recommended to loosen the injector by tapping it with a hammer after 1-2 turns. Since the old injector is already being discarded, there is no need to be stingy here. So, you cheapskates who want to get the old, used injectors back to sell, take note! Previously, it was just junk (otherwise there would be no reason to replace the nozzle), and then even worse afterwards.

With standard hand testers, only the first opening stage can be tested. Only a test bench with measurement of flow rate or pressure profile allows for reliable statements about the second opening stage.
Due to the spring system, changes in the first opening stage also affect the second opening stage. Practice has shown that if the first stage is properly adjusted, the second stage will also fit well.
For non-assembled nozzle holder combinations, it is sufficient to check and adjust the first opening stage when replacing the fuel injector.

When the nozzle holder combinations are damaged, the process quickly becomes extremely complex, as the internal structure of the 4 nozzle holder combinations can vary significantly. It is even very likely that this is the case.
Obviously, the manufacturing process only focuses on the correct properties of the finished nozzle holder combination, i.e., the opening pressures. Deviations in the mechanical/dynamic properties, e.g., of the springs, are "corrected" through mechanical adjustments. Mixing the contents of multiple nozzle holder combinations or not paying attention during assembly as to what was in which, is therefore a very bad idea.

With the correct adjustment of the first opening stage, a trick can be used to check the second opening stage to some extent without using complicated equipment: The component of the first opening stage is approximately 0.25 - 0.30 mm closer to the component of the second opening stage in typical nozzle holder combinations for the VAG VP37.

For adjustment, spacer shims are used that are available in 0.05mm increments of thickness. 0.05mm corresponds to approximately a 10bar pressure difference.
To achieve the most precise adjustment, the distance spacers can be lightly abraded with fine sandpaper. In practice, it has been shown that in extreme cases, this can improve the acoustic properties at idle. For example, with 3 nozzle holder combinations with an opening pressure of 182 bar for the first stage and 1 nozzle holder combination with an opening pressure of 198 bar for the first stage, sensitive ears may detect a slightly uneven engine run. This is also evident in the idle speed control measurement values in measurement block 13 of the engine control unit (Diagnostic tool: VCDS / OBD2 Profi-Diagnose KKL+CAN, HEX-V2, HEX-NET).
The values of the idle speed control should not be overemphasized, as many other factors also influence performance, such as the compression of the corresponding cylinder. Similarly, uneven running of the belt drive can have an impact, for example, a cam belt pulley that is not centered, or worn tension rollers.

To somewhat compensate for the inevitable minor differences in opening pressures between individual nozzle holder combinations and to optimize the engine's rotation, it is recommended to install the nozzle holders such that the ignition sequence alternates between one with a higher opening pressure and one with a lower opening pressure. The position of the needle holder combination with needle guide is fixed and should not be changed.
Good: + Deviation, - Deviation, + Deviation, - Deviation.
Bad: + Deviation, + Deviation, - Deviation, - Deviation.