The M104 has 2 sensors.

It is more complicated than just bolting on a couple of random sensors. The sensors are piezo electric microphones tuned to specific frequencies so every engine family is going to have a different frequency, sensor location.

The sensor needs to be physically mounted to the block in such a way that it does not vibrate. US engines tended to remove a block coolant drain plug and screw the sensor in there.

Someone has to of tested various sensors by now, it is just a subject that hasn't come up very often.

Try here

I think this is the original site
Welcome to diy_efi/efi332

This might be a different site
DIYEFI.org