MoTeC Global Forum

I have two knock sensors on the block. Is it possible to connect two SKMs on M800?

Hi Mazi,

Unfortunately the 'gating' process that the SKM uses would mean that it would not be possible to have 2 SKM's.

Hi Mazi,
Because we use a gated signal it means we are listening to each cylinder individually. We also have a gain factor on each cylinder so we can more or less turn up the volume of the single knock signal for cylinders that are further away. Even on V engines this has proven to be sucessful so there is no real need for more than one sensor. There may be the ability to use more sensors in the future but for now it all seems to work just as you would want it to with one sensor.

Isn't the SKM able to use upto 4 knock sensor inputs ? The literature shows it does.

It has the ability to monitor up to 4 separate knock sensors - but it can only monitor them one at a time. So even if you have 4 of them connected you cant use them all at the same time for knock control. As Mark stated since the SKM Gain values can be set to "normalize" or "normalise" (depending on which hemisphere you live in) the knock signature from each cylinder so that they all have the same intensity regardless of physical location of the knock sensor - only one knock sensor is sufficient for knock control.

Shane would there be a benefit to having multiple knock sensors?

My 2JZ engine (last model supra) block has 2 knock sensor provisions on the inline 6. The knock sensors are also narrow band sensors. The newer Lexus V8 engines use 4 wideband knock sensors. 1 knock sensor per 2 adjacent cylinders. I'm assuming the OEM ecu detects the knock thershold and retards timing accordingly. The inline 6 has a knock sensor at the #2 and #5 cylinder locations. I was hoping to switch to the newer wideband knock sensors if it would benefit the SKM to detect frequency over a wider range. I have the provisions of adding a third sensor in the middle of the #3 and #4 cylinders. I was wondering if having multiple sensors would make detecting knock any easier than the two the block already has provisions for. The sensors are a 8mm thru hole knock sensors with a 2 pin connection on the side. It maybe identical to the flat response Bosch sensors I've been hearing about except they are made by Denso.

Thanks in advance
-Joe