@Ulf and all the pump enthusiasts (long)

Hello,

wie schon im alten Forum diskutiert wurde bei meinem G3 Variant 1Z Mj96 durch einen Bosch-Dienst bei der Suche nach der Ruckelursache das Mengenstellwerk neu eingestellt. Eigentlich war ich mit dieser Justage auch zufrieden. Das Auto ruckelte zwar immer noch Verbrauch und Fahreigenschaften waren aber okay. Die Diagnose "defektes Mengenstellwerk" lies mich von einer Reparatur absehen. Nach dem Osterurlaub war ich geschockt über den Verbrauch: 8,1l/100km (mit Eigentumswohnung am Haken). Vor der Reparatur hatte ich einen Gespann Verbrauch von 7,5l/100km. Weiterhin beunruhigte mich eine extreme Anfahrschwäche die bis ca. 1800U/min vorhanden war. When I then drove a colleague's car (also a 1Z) that didn't have this starting problem, I decided...I want to adjust the ESP settings again, according to my own preferences.

WARNING!!!! What follows is not a general guide and, as Ulf already pointed out, it's a very difficult undertaking. If you don't have the appropriate tools and measuring instruments available, you should avoid attempting this.

Um die "Originale" Stellung des Mengenstellwerkes zu ermitteln habe ich meinen Meßschieber bemüht und den Abstand von zwei Punkten an dem Pumpendeckel und der Halterung am Motorblock ermittelt. Dann habe ich den Deckel gelockert und den Deckel 0,3mm weise nach "fetter" gerückt und immer wieder Probegefahren. An dem Punkt an dem sich das Standgas dann nicht mehr auf 880U/min zurückregelte habe ich den Deckel wieder in Richtung "mager" verschoben. DThe result was very interesting.
THE JERKING IS GONE!!!!!?????
2. After a sudden surge of gas, the idle speed doesn't return to its original setting as quickly (so it needs to be adjusted to be leaner again).
3. The problem with starting is GONE!
4. In the area around the thrust cutoff engagement (1400-1600 U/min), a slight oscillation of the engine unit can occur, especially with minimal gas input (still within acceptable limits). If you release the throttle or apply it very gently, everything returns to normal.

I only tried using a hook for my apartment on short distances, and subjectively, I felt it was more comfortable to drive with.
Should I perform an "Ulf" pull test with my vehicle and trailer combination, which weighs approximately 2500 kg?
- How can I restore the original settings (before the Bosch service repair)?


Best regards, Bertil.

Hi Bertil.

While the fact that you eliminated jolting by adjusting the turnout track to a "fatter" setting contradicts my previous experiences (the fatter the setting, the more jolting it usually is), it's still an interesting observation.

As a general cause for the jerking, I currently suspect issues in the transition area between idle speed control and throttle-dependent engine management: if there are significant differences in the required fuel injection amount when switching between these fundamentally different functions, this could ultimately lead to the known jerky behavior. (Purely theoretical; does anyone know something better?)
I cannot confirm from my experience that the thrust cutoff threshold should be at 1500 rpm: My AFN and my wife's ALH switch off in thrust mode at every speed above 900 rpm.

I also don't know how to restore the original pump setting without a test bench or a documented reference measurement value.
Approximately(!), it could involve using a test range of 2000 - 4000, if all measurement conditions are known (rolling circumference!!), and then adjusting the pump until you achieve the calculated value from the table as accurately as possible.
What is also naturally required is a completely intact engine; otherwise, one might try to compensate for performance deficiencies caused by worn nozzles, insufficient boost pressure, etc., by adjusting the fuel pump too generously .

Hello Ulf,

If I increase the pump's output significantly, it starts to jerk violently -> correct.
According to Bosch service documentation, the thrust cutoff threshold for the 1Z engine is approximately 1500 RPM (although I only realized this after experiencing the jerking).
The nozzles are brand new (all of them).
The difference in the 2000-4000 RPM sprint time before and after my adjustment was about 0.2 seconds, which probably doesn't say much. When the engine was getting full boost, the performance was okay, but before that (below 2000 RPM), it was a disaster.
On my test hill (accelerating from a standstill and always revving up to 4000 RPM), I was just as fast as I was four years ago when I made my first attempt there. Before and after the adjustment by the Bosch service, I had almost identical values. I think the injectors were the problem (one of them was leaking back then).
I can confirm your suspicion that the jerking is caused by a poor transition, but only if the jerking occurs within a narrow RPM range.

I only hope that our experiments will be helpful to others.


Best regards, Bertil.