Two Knock Sensors Per Knock Module Channel?

[Tjabo]

First of all, I apologize if this isn't the most appropriate forum in which to post this question, I was torn between this forum and the MS3 General forum since the knock module is for MS3 only. There just doesn't seem to be a lot of discussion about it anywhere on the board.

So anyway, my question relates to the BMW M62 V8s. There are two knock sensors on the inner surface of each bank of cylinders. They come into the factory ECU on four separate wires. What I was wondering was whether the signals for the two from each side could be joined into a single wire coming into a channel of the knock module? The sensors appear to be the normal Bosch broad spectrum sensors that have a bolt through them holding them to the block, and they have the standard old fuel injector style wire connector.

Thanks to whoever can help with this!

Thad

[phoenix3d]

Hi Thad...

I would suppose it should be do-able... As seeing that each sensor generated a voltage at the respective frequencies that they were designed for and that the Knock module is pretty much listening for the noise (albeit at a specific "Volume") All I foresee is that you may have to play with the Gains. And not sure of the Knock Per Cylinder feature would still be applicable, Nut I don't see why not.

But Please Note.. I may be Completely Of the Line here.. I would suggest some feedback from gurus Like James (JSMcortina), Bruce Bowling , All Grippo and the like.

Gordon

[Tjabo]

Thank you very much Gordon!

I know those guys are all very busy, so hopefully one of them will bump into this thread and share their thoughts.

Cheers!

Thad

[arran]

Thinking out loud here, basically I don't think there is any point connecting two knock sensors to a single channel.

With a normal config having a single sensor driving into the electronics, you have a lowish impedance source (the sensor) driving a high impedance sink (the amp).
Typically the electronics would offer mega ohms of input impedance, this is a generalised principle, the idea being that a sensor needs to be able to drive MORE current the lower the input impedance of whatever it is connected to. Knock sensors will only be able to deliver a tiny amount of current, so if you try to drive something with a significantly lower impedance, you are going to substantially damp the signal swing (think V=IR).

With two sensors connected together, what I think will happen is that they will be driving a very low impedance and so the amp won't see very much signal to work with. The reason for this is that if you position yourself at one of the two sensors and look out along the wire, you will see the impedance of the amp (high impedance), and also the impedance of the other knock sensor, in parallel. A quick google tells me that the sensor will typically offer 500 ohms, which is very low in comparison to the amp. The resultant impedance of the two loads in parallel will be almost the value of the other sensor, 500 ohms. The situation is obviously the same if you consider the other sensor.
The sensors just would not have enough grunt (they are just a microphone) to drive 500 ohms.

Arran Coote, Electrical Engineer

[Sheriffpower]

First of all, I apologize if this isn't the most appropriate forum in which to post this question, I was torn between this forum and the MS3 General forum since the knock module is for MS3 only. There just doesn't seem to be a lot of discussion about it anywhere on the board.

So anyway, my question relates to the BMW M62 V8s. There are two knock sensors on the inner surface of each bank of cylinders. They come into the factory ECU on four separate wires. What I was wondering was whether the signals for the two from each side could be joined into a single wire coming into a channel of the knock module? The sensors appear to be the normal Bosch broad spectrum sensors that have a bolt through them holding them to the block, and they have the standard old fuel injector style wire connector.

Thanks to whoever can help with this!

Thad

Hi, have you got join the two cable in one single wire ? Thank's

[Tjabo]

I did not. I ran E85, so I just scrapped the knock sensors all together. Sorry!