Knock sensor, low power 3.2 2008 S80

[Loss80]

Hi, I have a problem with my Volvo.

It started with a misfire. I replaced two coils, and it was fine for a while.
Then the misfire problem reappeared, so I replaced the spark plugs and another four coils, all with new ones. It was better for a few days, but the problem returned.
I read that misfires are often caused by a faulty differential pressure valve (PCV), so I replaced it, and it was fine for two weeks until another problem arose.

The fuel knock is present, both on petrol and LPG. The intake manifold gaskets have been checked, the air flow sensor has been replaced, the air filter is new, and the throttle body has been cleaned.
The car can be driven all day and everything is fine, but sometimes, while driving near a shop, an error code appears: the car has no power and the RPMs are low. Error P0333 appears first, and then other errors may appear. I've read many forums about this error, but no one has mentioned its cause. According to mechanics, the knock sensor never fails, and replacing it won't solve the problem.

Can anyone help me?

I apologize for any spelling errors, but I'm using a dictionary to communicate in a foreign language.
They can't help me in Poland.

[Vova585]

Knock sensors are not immune to failing. It is rare occurrence, but is possible. There are many issues that can cause this fault code and simple part replacement may be costly without much help. First possibility is fuel injectors. If the car does not run a lot on regular fuel/patrol but mostly on LNG, it will lead to injectors being "dried" and thus no longer spraying normally. I am not sure of the default strategy of your fuel system when it is using LNG and when patrol, so hard to tell. I would start with removing all injectors(decently easy) and send them for professional cleaning and test(plenty of places in Poland will be able to do it i guess) so they will tell you how many ml(s) of fuel injectors were producing prior to cleaning and how many after. Also comment on the "cone" pattern of the spray vs "needle spray" pattern(basically instead of cloud of fuel you have single small stream which will not be igniting as efficiently). Replace lower and upper O-rings prior to reinstalling injectors into your car. Switch to only patrol mode, clear all the codes, drive around and see what codes it will return.
2nd possibility- problems with the timming chain being overstretched and causing all sorts of problems. Would be nice to have someone with good in cylinder tranducer scope test your car. (Oscilloscope of postolovsky will be quite familiar name for many in eastern europe). Waveform will show you possible timming issues, possible issues with catalytic converter creating backpressure, relative compression in cylinders).
3. Mechanical engine problem causing "knocking" and thus sensor sends signal to change ignition timming. You can unbolt the affected sensor(likely bank 2 or sensor 2) and isolate it in something "soft" which will prevent it from banging around engine compartment and send false signals. You may need to extend the wiring to do that vs just wrap it in something soft non flammable and secure to plastic element if able.
4. You can also go to "shrot"(salvage yard) and get used sensor from similar engine. Or buy brand new ones if able to afford.
5. Based on my quick search it appears that both sensors are connecting to 1 connector. If possible, it would be great to swap both sensor and see if the problem remained the same or now "1st" sensor reports issue since was moved to the problematic engine area. Not sure of the wiring harness is long enough to do so.
5. Fantastic scenario- you are able to find proper mechanic with tools and knowledge. He performs testing woth Oscilloscope and tells you all the info as above. He also tests voltages and signals at the connector and graphs them. After all that he gives you definitive diagnosis.
Glory to Poland and good luck
P.S. it would be nice to have "freeze frame" data to see what conditions were present when ecu turned on this code. Seeing fuel trims also will be great to understand what your ecu is seeing. I doubt you would be able to find tech equally great in LNG and patrol, it is usually one or another. Concentrate on making sure car runs good on fuel first and then you can work on LNG