I installed the B18C GSR motor in my 93 Civic and it was a transmission conversion as well (auto-manual). The ECU keeps on shooting code 23 (knock sensor code) whenever the motor passes 4000 RPM. There are no signs of internal knocking or detonation but at the same time, it seems like the knock sensor is doing its sensing job as the CEL only lights up once the motor reaches 4000 RPM. I haven't replaced the sensor yet as it is a $240 part at Acura. Does anybody know, most likely, what the cause could be? Either bad sensor (over-sensitive sensor?) or faulty ECU I suppose? Thanks for any help.