ok i put a b20b into my 90 civic si. motor runs great no problems except after the car warms up and has been driven for about 20 minutes the cel pops on the dash but not on the ecu. i have tried 3 ecu with the same result. car doesn't run any different after the cell comes on, still runs great. by the way i have searched and didn't come up with anything. thanks in advance

 

Mine did the same but it was due to the ECU looking for the EGR. Maybe the same for yours.