Thanks for further ideas. O2 sensor gives 0,47 V at idle. The output from X11 pin 3 is steady around (AC) 4,7 V, (DC) 2,6V. The value raises only when decelerating. With a voltage on 4,7 V the duty cycle is 65%, and with 2,6 V 80%. I have tried another EHA and the voltage to it is 13,4 V.

While testing I accidentaly disconnected the ECU and the engine kept running like before - how is that possible?