Chief Robert

All y problems started when my CEL lighy went on last December for a malfunctioning Knock Sensor. I had the Knock Semsor replaced by certified mechanic. Afer installtion on the test drive, after a mile of so of driving the CEL light was on again for the same reason. At this point, the mechanic decided to look and test wiring from the Knock Sensor to the ECU. All was OK. After all troubleshooting, it was decided that the ECU was the problem. So I bought a used one online for a 2003 S2K - same model as mine. After ECU install, this tim the car wont even start so back to Square 1. Is there a procedure for installing a different ECU on S2000s. Thank you for all your help.

AP1Theory

US spec ECUs has a built in anti theft device built into the ECU that only allows you to start the car with the prigrammed key. So when purchasing a used ECU, make sure you get the key that came out of the same car as the ECU so that you can program a new key to that ECU.
Or you can get a JDM ecu that doesn't have the same security built in.

s2000maniac

I doubt the ECU is the problem. Double check to make sure that the mechanic didnt break the knock sensor.