[ainarssems]

Just my 2p about knock sensors.
1. Old or poor fuel.
2. Carbon build-up in in combustion chamber due to historic use of poor fuel, mostly being driven short distances not getting up to temp or high oil consumption.
3. Knock sensors bolted down with wrong torque values or loose. Or something else loose on the engine vibrating away giving false knock reading.

My friends 3.7 was like that, sometimes showing error codes and in measuring blocks always showing high knock values and ignition timing retarded due to knock values. Car did not seem like cared before and he was always driving on cheapest Morrissons petrol. Put in VPower just for trying and values went down quite a bit. He could not be bothered and just went back to Morrissons fuel. Probably cost him more in increased fuel consumption due to ignition timing retardation than he saved in cost per liter.