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Has anyone fitted a wire in g4+ extreme to an rb20/25 using the factory single wire knock sensors?
I recently did so with some strange results. With the knock frequency set to 6 or 7 khz and the gain at 1 ~ 3 the measured knock levels are at zero. Increasing the gain to 4 and greater numbers yields some knock levels that increase as expected with RPM but they are in the range of 10 - 100. I'm curious is it typical to have the gain set to these values to pick up the signal. Generally on the other g4+'s i have installed on evos and 3sgte's for example the gain set at 1 yields good results.
I generally prefer the Bosch 2 wire knock sensor, and find you get a clean and consistent signal almost irrespective of the engine. With the single wire sensor, the ECU is going to measure the voltage from the sensor relative to the chassis ground or wherever you have the ECU grounded - hopefully to the block. This can effect the signal level, particularly given the voltages from the knock sensor are relatively small.
Our 350Z is configured with a gain of 4 so I wouldn't consider this is unreasonable, although this does yield peak values of around 400-500. Check your cylinder gains too and ensure they aren't set really low for some reason. Ultimately I'd try tuning the system and see if it's effective in detecting knock. That's really the bottom line.