Knock Sensor Output (Again).

[Tom Cloud]

>     Sorry to get back to covered ground.....
>     
>     I have a question about the outputs of a knock sensor.

 - if you're unsure whether it's AC or DC (and don't have a scope)
use a DMM (not an analog VOM) .... the reason is that a standard
digital multimeter will have a capacitor (condensor ;-) blocking
the DC voltages when it's on the AC range (where an analog VOM
does not -- it will read DC even on the AC range).  IOW, the
DMM will only read AC on the AC range, not DC so you can determine
the DC and the AC component of a signal with a DMM

 - the normal engine noise will probably mask any knock signal --
it's apparently quite difficult to ferret out (until it gets very
severe), so very narrow notch filters are used at specific frequencies
where knock is known to exist

I've just put a knock sensor on my 351W and hooked it to an audio
amp -- it's just a bunch of noise to me  8^)   The Probst book on
Fords says that knock occurs at certain known, and very narrow,
frequencies peculiar to specific engines -- those frequencies being
from about 6 kc up to over 10 kc

Tom Cloud

   If there was a funeral at night, would all the cars drive
    with their headlights off?