Citroen C8 Engine Power Loss Whistling Noise

I had a similar issue with my C8! Those symptoms sound awfully familiar. The whistling noise and hissing, along with the reduced power, really point towards a problem with the turbo system. Have you checked for any obvious boost leaks? Maybe a cracked hose or loose connection? It could also be the pressure sensor giving false readings. Is the turbo wastegate working as it should? Mine was a pain, so I feel your struggle.

Thanks for the quick response! I haven't specifically checked the pressure sensor yet, but I did visually inspect the hoses, and they seemed okay at first glance. However, I'll definitely take a closer look for any subtle cracks or loose connections. What exactly did you experience with your turbo wastegate? Any specific tests I can perform to check if it's functioning correctly? Also, where is the electrical bypass valve located? I'm not entirely familiar with the turbo system components.

Okay, so with mine, the wastegate was sticking, causing overboost at times and underboost at others. This would throw the engine into limp mode and generate similar symptoms to yours. As for the bypass valve, it's usually located near the turbocharger itself. Given all the symptoms you describe, honestly, I'd suggest getting it checked by a workshop. They'll have the tools to properly diagnose the turbo system and pressure readings. It could be the actuator valve, but without the right equipment, you might be chasing ghosts.

Thanks for the advice! I took your suggestion and brought it to a workshop. Turns out it was the electrical bypass valve, just as I suspected. They replaced it, and the total repair cost was 250€. The car is running perfectly now; no more check engine light, full power restored, and the whistling noise is gone. Thanks again for pointing me in the right direction!