knock, knock! Who's there?

[John Lagnese]

Knock is predetonation. It is when the gas ignites before the spark plugs
ignite it at the correct piston position. Higher octane gas does stop this.
However, if your engine is not knocking or pinging, higher octane can be
wasted money. If the engine has a knock sensor, a small microphone like
device, the engine will retard the timing to stop the pinging. It reduces
power and mileage.
John
-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com] On
Behalf Of Tess McMillan
Sent: Sunday, July 22, 2007 11:56 AM
To: quattro at audifans.com
Subject: knock, knock! Who's there?

So what actually is a "knock"? 

How can you have a knock only at certain rpms?

In response to my query about a CEL that was going off (and which is no 
longer doing so), someone responded they thought I could have a faulty 
knock sensor. Would this by itself cause "knock"? What about if you've had 
cam modifications? The knock is about where the power band starts; beyond 
that, and below that, it is not present.

For some reason I thought poor gas caused knock.... The minimum I use is 
92, sometimes I'll opt for 100 when I can get it.

As usual, thanks for the education and advice &:-).

Tess

in Bellevue, WA USA



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