Knock sensor band pass filter

[Dave WM]

having a bit of an issue getting a knock sensor that will work with a 300zx turbo 1986 ecu and an L28et block.

found a sensor from nissan but when I looked at the scope with it installed on the running engine I was getting all kinds of voltages that I would assume be problematic. My guess is the flat response vs resonate is the issue. Pretty sure the doughnut type I am using is a flat response type. 

 

the rc value was selected since the ecu seems to want a specific value to not set a code, there is a bias voltage that is dropped by this resistance. The r1 was selected as I assumed the lower value would pass more signal.

The stock sensor in a L28et has a resistance of about 750 ohms, which sets the error code. Left disconnected (infinite) also sets the code.

I used the nissan senor that was about 500k and no code. will try the 330k and see, if not will adj up to the 500k and reset the C2 

that C2 56pf seems like a very small number for any kind of audio frequency, but that is what the calculator called for with the R2 value.

 

so here is my next try...

 

Edited May 22 by Dave WM

[Captain Obvious]

I don't know anything about knock sensors other than they are piezoelectric. Piezoelectric materials change shape when a voltage is applied to them, and conversely... when a piezoelectric material is subjected to a shape change, it generates a voltage. That's about all I know.

Do you have any links or learning sites that do a good job of explaining more detail than that? How this pertains to knock sensors?

[zKars]

https://phormula.com/knock-frequency-calculator/?fbclid=IwAR1dO8_Qw8lferQVBmn7h66PiqEi3_FtGA5hvaXtLDI-7r5ed6ihA8VfxeI

All of the aftermarket ECU vendors (Haltech, MegaSquirt, etc) that support knock sensor inputs have some documentation related to the subject. At least you can see the input screens and review what types of inputs are needed. 

It’s all about finding the frequency band where knock occurs on your engine. And mechanically about putting the sensor where it can pick up the noise properly. Engines that never had knock sensors don’t have convenient places to mount one in the “right” place. You have to get creative sometimes. You can’t just duct tape to the side of the block.

The only knock sensor on an L series is on the 82-83 ZXT in the block just below the head.

Edited May 23 by zKars

[zKars]

 

https://www.viatrack.ca/

 

Edited May 23 by zKars

[Dave WM]

I have the L28et block, and the knock sensor that goes with it, just not sure its compatible with the 300zxt ecu, very confusing stuff. Prob the smart thing would be to just use the one that it came with (the 800 ohm sensor that keeps creating the error code) and see if it knocks in use. From what I have found so far is the knock freq is about 6.5k and if I go with a flat response sensor (not tuned just outputs AC at what ever freq it sees when vibrating the piezo crystal) in order to get any usable info from it I would need a narrow bandwidth, prob an active filter. Since for now I am sticking with the OE ecu from the 1986 300zxt my options are pretty limited as far as tuning.

The best course of action really seems like just install the thing and see how it runs....