DIY solution for starting engines with VP 37 (Articles)

If a 90 or 110 HP TDI engine tends to stutter or jerk when rolling or accelerating slightly at speeds below approximately 1300 rpm in higher gears, a slight reduction in the injection quantity can help. This can be achieved either through adaptation using VCDS or by mechanically adjusting the pump's delivery rate (by shifting the upper part of the pump with the control mechanism on the pump body).
While this process does result in a slight loss of horsepower, the often excessive power output of the TDI engine typically only approaches its stated value without actually falling below it, provided the modifications are not overly aggressive.
Furthermore, drivers using power boxes can often compensate for power loss by adjusting the settings on the power box.

A good indicator of the throttle position is the engine returning to idle speed after brief bursts of acceleration, typically around 1400 rpm: Ideally, when you release the pedal, you should only hear the mechanical sounds of the engine for a short time; the actual combustion noise (a controlled knocking) should only become clearly audible again when the engine reaches 900 rpm.
Then, (at least with AFN, based on my experience), you shouldn't expect any stuttering or lag.

If there is a tendency for the engine to surge due to a high fuel flow setting, the combustion noise will at best become quieter when the pedal is released, but will become clearly audible again at around 1100 rpm (or even higher).

Within certain limits, the fuel flow rate can be adjusted using VCDS adaptation, which essentially shifts the stored pump characteristic curve in the software. Given the significantly lower risk of damage compared to mechanical intervention, this option should definitely be tried first.
At idle speed (engine warm, electrical consumers and air conditioning off), the fuel injection quantity should ideally be around 4 mg as displayed in the measurement block; significantly less (< 3 mg) can contribute to misfire problems.

Perform a login using the credentials "12233" and, in the "Settings" menu, select channel 1. Enter a lower value than the saved value (for 5-digit values, decrease in steps of approximately 20; for 3-digit values, decrease in steps of 2) and save the change. Subsequently, check the injection amount to see if it is approaching the target value (approximately 4 mg).
Unfortunately, the adjustment range is not very large when using VCDS. Beyond the "attack" of adaptation, no smaller or larger values are considered.

If the adaptation process is not sufficient or VCDS is not available, one should consider the following correction, which requires not only feeling and patience, but also must be carried out with absolute care and precision.



Warning:
If performed incorrectly, the engine may not start at all (without initially causing any consequential damage).
An excessive correction of this error or a shift of the control lever directly in the wrong direction can cause the engine to immediately rev up to harmful RPM ranges (well over 4,000 rpm) without any throttle input, which can potentially lead to serious damage (collision of valves and pistons, connecting rod failures, etc.)!

First, be sure to mark the position of the pump's upper part (with the cable connection) on the pump body using a pin or similar tool.
Without the marking, the original (approximate) position is practically impossible to reproduce after excessive adjustment!

After the engine is running, loosen the triangular screw on the pump cover and the 3 lower Torx screws in a criss-cross pattern, first only by 1/8 of a turn, then another approximately 1/4 of a turn.
Then, shift the pump housing slightly towards the timing belt (on the order of approximately 1/20 to 1/10 mm; this is barely visible on the marking!). Unfortunately, the rubber sealing ring in the upper part makes precise adjustment difficult due to its tendency to rebound.

Gradually tighten the screws, start the engine, and pay close attention to the engine's behavior during the described sudden acceleration test. If it returns to idle speed more quietly (and quickly), then the adjustment was generally successful.

If the power loss during operation proves to be too significant, one should aim for an intermediate value in a subsequent adjustment.
Don't get discouraged if it's still not perfect after the third attempt. If necessary, use a magnifying glass to better see the adjustment.

Those who have access to VCDS can quite accurately check the result, as described above, by examining the displayed idle injection volume. When the reading is approximately 4-4.5 mg, the pump is adjusted in such a way that any disruptive jolting should normally no longer occur.

The pump can handle several adjustments without leaks or stripped threads, as long as you don't handle it carelessly.

Regarding the SDI: if they are experiencing similar problems, the solution described here should also be applicable.


By reducing the injection amount (either mechanically or via VCDS), it may be possible to... Starting problems are occurring.
A solution can generally only be achieved using VCDS: log in again with "12233" and enter higher values in channel 5 (in steps of approximately 30 for 5-digit values, and in steps of 3 for 3-digit values) until the starting behavior is normal again.


Similarly, chips/dirt in the area of the metering station can cause jerking, see: https://community.dieselschrauber.org/en/viewtopic.php?t=5517

[Translating...]

Hallo,

heute habe ich Ulfs Vorschlag angewendet. Tatsächlich lässt sich der unruhige Leerlauf beim Rollen zwischen 1 und 30km/h meines AHF durch Verschieben des Pumpenoberteils vollständig beheben.
Bei Leerlaufdrehzahl von 900min-1 wurde vorher eine Einspritzmenge von ca. 2,2 mg/Hub über die Diagnoseschnittstelle gemessen (Klima aus, kein Licht, Motor betriebswarm).
Bei Meßwerten ab 6mg/Hub verschwand das Ruckeln vollständig, ab 3mg/Hub trat noch eine deutliche Besserung auf.
Da bei den höheren Werten zwar absolut kein Ruckeln mehr zu provozieren war, aber auch die Leistungsentfaltung deutlich zäher , habe ich nun 3,2 mg/Hub eingestellt.
Damit sind nur noch mit ausgeschalteter Klimaanlage leichte Leerlaufschwankungen beim Rollen spürbar.
Ergebnis: Ulfs Tip ist auch beim unruhigen Leerlauf des AHF anwendbar.

Grüße, Rainer