Dear Forum,

i'm from Germany and i am owning a Opel Astra OPC with the A20NFT / LHU Engine.

Unfortunately my fuel pressure (both low and highpressure) fluctuates when idling and at medium load.
Furthermore, the fuel pressure drops from 4 to 3.5 bar /50psi under full load.
This results in a shaking above 5500rpm.

No check engine light - no errors on the ecu.
Boost pressure, ignition timing, injector duty cycle are showing nothing but smooth curves.

My workshop installed a new fuel pump on it, which did not change anything.
Now they don't know what to do and would start swapping parts wildly.

Now I have noticed that when I remove the pre-cat o2 sensor the engine runs very quietly and nothing fluctuates.
Also the sound of the highpressure pump changes.
If the fuel pressure oscillates, the pump clicks about 1x per second.
When the lambda sensor is disconnected and the fuel pressure is stable, the pump makes a clicking sound in time with the injectors.
My car dealer can't even tell me which of the two is the right one.

The engine and also the O2 sensor has only 6000km on the clock. (First Engine died because a faulty sparkplug wich... "dissolved"..)

Maybe you guys have a hint for me where i could start searching for failures?