I got a 91 civic si with a obd o jdm b16 swap im using the jdm ecu with the swap i have no check engine light at all i have both o2 sensor an i changed out the fuel filter cap an rotor new nology wires an plugs car starts up fine the problem im having is when u start to drive the car hesitates around 2300-3500 rpm it dose it enought too slow me down but if it more gas it picks upp i read that it could be the main relay could it be anything else

 

Swap the O2 sensors around, that did the trick for me.

 

wouldnt the check light be on if it was the other way around

 

no if you search you'll find the o2 switch is common as the usdm plug works on the opposite sensor. however, i have done the switch and i also get a little hesitation. i think i just need new sensors