knock sensors

Seight-V8 · Post by **Seight-V8** » Thu Apr 28, 2011 3:03 pm

hello all,

anyone know what voltage the GEMS type 4.6 knock sensors use?

its the ERR5594 (blue) type sensors...

cheers

scottt

ChrisJC · Post by **ChrisJC** » Thu Apr 28, 2011 4:16 pm

RAVE says:
"The knock sensor produces an output voltage which is proportional to mechanical vibration caused by the engine"

So I'm not sure what you mean?

Chris.

Seight-V8 · Post by **Seight-V8** » Thu Apr 28, 2011 11:01 pm

one side of my v8 is getting 1.5v and the otherside nothing...

Just wondered if it should get something like other sensors.....ie 5V to make it work.

Could find much info so thought i would ask.

cheers

scott

ChrisJC · Post by **ChrisJC** » Fri Apr 29, 2011 7:15 am

Hmm, I wouldn't like to speculate on what signal should be present.
RAVE doesn't say anything about that, it basically says if the OBD tells you to replace a knock sensor, then that's the answer!

But it would seem logical that both have the same signal on.

Chris.

DaveEFI · Post by **DaveEFI** » Fri Apr 29, 2011 8:36 am

Seight-V8 wrote:one side of my v8 is getting 1.5v and the otherside nothing...

Just wondered if it should get something like other sensors.....ie 5V to make it work.

Could find much info so thought i would ask.

cheers

scott

They are generally a piezoelectric microphone so don't need a supply voltage. They actually generate one. The signal from that mic goes to an amplifier which has a shaped response curve centred around the knock frequencies. When that signal exceeds a pre-set level it triggers ignition retard. But this will all be built in to the main ECU, I'd guess.

The only way I know of to check a sensor would be with a 'scope - or by substituting a known good one.

ChrisJC · Post by **ChrisJC** » Fri Apr 29, 2011 12:35 pm

DaveEFI wrote: The only way I know of to check a sensor would be with a 'scope - or by substituting a known good one.

I believe they are piezo based, which means they are a capacitor. If you had access to a 'Bridge', you could measure the capacitance of two, and check they were the same.

Chris.

Seight-V8 · Post by **Seight-V8** » Sun May 01, 2011 2:35 pm

i gather from this then there shouldnt be any voltage supplied to these from the ecu.

At the moment one is getting 0v and the other 1.5v, so its making a loud high pitched sound when the ignition is turned on.

need to find out why its been supplied a voltage next.

cheers

scott

DaveEFI · Post by **DaveEFI** » Sun May 01, 2011 5:58 pm

Seight-V8 wrote:i gather from this then there shouldnt be any voltage supplied to these from the ecu.

At the moment one is getting 0v and the other 1.5v, so its making a loud high pitched sound when the ignition is turned on.

need to find out why its been supplied a voltage next.

cheers

scott

Many microphones, if fed with an AC signal, will act as a loudspeaker.