Dear all,

I own a 2001 S60 MT 140 HP but I'm posting this question at the 850 forum because it is rather unknown at the newer S60 and you guys of the 850 forum have more years of experience.

After about 20k kms I noticed slight knock during acceleration. At normal driving conditions even at full throttle in 4th gear there was no knock audible. Only at about 1000-1500 rpm under acceleration there was knock audible. Dealer checked out everything and eventually replaced spark plugs which indeed reduced the knock. It was only slighty audible at temperatures above 14 deg centigrade (57 F). I was using (in the Netherlands) so called Shell Pura which is a RON-95 with cleaning additives.
The car was taken for a power test and delivered the full 140 HP (motor) power with normal RON-95.

I turned out with the normal RON-95 gas or RON-98 NO knock was audible at all. (The test I always did was: Full and half throttle in 2,3,4 from about 1200 rpm). That all was about a year agoo.

Last October by occasion I did full throttle in 2nd gear window down, and I could hear again this "zzz" "zzz" noise at about 4000-4500 rpm! (T=14 deg C/ 57 F) I used RON-95.

My questions
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Is this knocking behaviour @4000-4500 rpm in 2nd gear full throttle using RON-95 normal??? Should I worry or not? Why can I actually HEAR the knocking (see comment 4)?

Comments
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1. No error messages
2. Car drives actually perfectly
3. At normal driving even full throttle acceleration in other gears, no knock audible
4.=> THIS IS THE ONE I DON'T UNDERSTAND: Always thought that the knock sensors are much faster than I am in detecting knock and that the ECU would command to retard ignition/ enrich mixture immidately, so I would not able to actually HEAR the knocking? (Remember that I could also HEAR knocking at about 1200 rpm using the Shell Pura gas, and noting audible with other gases (why was the ECU not taking action when the knocking occured with the Shell Pura?)

Thanks very much in advance for your replies,

Dutch