I´ve managed to dig out some info on them and it seems the signal is very low .
Below 0.7v , the square wave length contains the dwell obviously.
How can I change the 5v logic level into something like 0.7v for upto 6 channels?
Then it is most probably current signal not voltage (as bipolar transistors have). You need to knew what resistor uses OE ecu in series (or how miliamps). If it's not possible, I would try 2.2 KOhm at first.
I´ll get a ecu and have and trace it.