Knock Sensors

[Bl4cK32]

I found a few things on the net about them, and was wondering if anyone found them to be interesting....

the first:

knock sensors on engines are set to detect knock at a certain frequency range, and shaving as little as 0.5 mm from the cylinder head can render the knock sensor completely ineffective as the change in combustion chamber also changed the frequency of the detonation, and they know this because when they stripped the motor and saw the detonation damage, they knew they had not recorded detonation via the knock sensors and I am sure this would not be widely known

The second:

A knock sensor can usually be tested by rapping a wrench on the manifold near the sensor (never hit the sensor itself!) and watching for the timing change while the engine is idling. If the timing fails to retard, the sensor may be defective -- or the problem may be within the electronic spark timing control circuitry of the computer itself. To determine the cause, you'll have to refer to the appropriate diagnostic chart in a service manual and follow the step-by-step test procedures to isolate the cause. Sometimes a knock sensor will react to sounds other than those produced by detonation. A noisy mechanical fuel pump, a bad water pump or alternator bearing, or a loose rod bearing can all produce vibrations that can trick a knock sensor into retarding timing.

Any thoughts??

[JimX]

There are cars with mechanical fuel pumps in the engine bay AND knock sensors?! No way!

[Sydneykid]

Hi Guys, we had a car with an open wastegate pipe that used to set the knock sensors into a frenzy.

I don't know about the frequency of the knock being a problem, you would have to check the knock sensor specifications to determine its listening frequency range. But I have used RB20DET knock sensors on RB31DET's and they read the knock levels perfectly. That kinda discounts the "cylinder head shaving" theory.

Hope that adds to the thread.

[sewid]

The moral or this story is that not everything you read on the net is true.

[ix9]

what's the normal amount of knocking that should occur... I'm running an AFCII on knock sensor 1 and gettin "10" on the knock display....