LJ.925

I put 4 gallons of 100 oct last night to see if a could eliminate what sounds like pre-ignition in may car. I'm in CA (91 oct) and I'm stock, but I've had this intermitent noise forever that I've always thought was turbo related. I even had the dealer look into it about a year ago and they weren't able to hear anything.

The noise usually happens under heavy load/throttle usually in the 3-4k rpm range. Usually in 3rd or 4th gear. I think it gets worse when its warm, but it was only about 65 yesterday and it still happened.

It just occured to me that it might be pre-ignition, so I upped the octane to about 93. I was still able to create the noise but I've driven the car less than 50 miles. Due I need to run a couple of tanks of 93 thru my car to verify this experiment?

Thanks,

L.J.

john s

If knock is detected the ECU will retard timing from the baseline map points. No knock, no retard. If you're hearing the same noise either it's not knock or the knock is so bad that the extra octane is insufficient. If it has been doing this for a year it's unlikely to be excessive knock. The motor would have been ruined by now. If it's a resent car, borrow someone's VAG-COM and take measurements.