GM knock sensor thread Options

[lagos]

is that an ATS TB inlet? looks nice. i ordered one last week!

Yup, I ordered that and the GM Knock Sensor Conversion for Doc to install. Along with the healthy dose of goodies that he's putting in the car.......should be really niiiiiiice.

i woudlnt recomend using the GM knock sensor. it dosnt work correctly for our cars and ats should stop selling it imho. keep the stock sensor.

[lagos]

and finally ....FOR THE WIN....

a copy of the toytoa bible (better then the bgb) from auto shop 101. that proves that each knock sensor is tuned to a specific frequency and that the ecu dosnt do any from of audio filtering to get its knock info from.

http://www.autoshop101.com/forms/h38.pdf

Very good link. I probably have that downloaded in the tech director on my other computer... I just haven't read it yet!

So, here's my *opinion* on what's going on in the knock system: Knock sensor sees knock even and resonates at a larger amplitude (shown in the graph on the second page). This signal is sent to the ECU where there is an envelope filter that is able to grab the peaks of the knock events. When this peak reaches a certain value, the knock response of the ECU is generated. In this way, the ECU can have a simple comparator watching the knock system - cheap and effective. (at one time, started investigating designing something like a J&S with a friend of mine...). There is no need for complicated electronics or computation in the ECU.

The resonant effects of the motor (peaking at the same or similar frequency as the sensor) will enhance the sensitivity of the sensor to knock events. BUT... the bandwidth of the resonance of something as complicated as a motor (with a shape NOTHING like a tuning fork and made up of many materials) should be fairly wide - and thus a sensor that is less than 1kHz away in peak frequency should still work well.

Once again, my opinion - but a fairly educated guess.

-Charlie

just read that pdf. tells you exactly how it works...lol

[phattyduck]

just read that pdf. tells you exactly how it works...lol

I did read it. Just because that's what they tell their mechanics what is going on, doesn't mean it is 100% technically correct.

In an interesting side note: There were some Subarus built with 'overactive' knock sensors. The recommended fix from the factory: a small amount of teflon tape on the threads to insulate it from the knock vibrations... On the flip side, some of the earliest US WRXs were shipped with almost deaf knock sensors. The result? About an extra 30hp and all those great reviews of the WRX (and that 5.4 second 0-60 time) and then the motors eating themselves alive after a while.

-Charlie