Chevy s-10 Knock sensor problem

Hi.
I've recently got a Chevy s-10 1999, its original engine was taken off and we installed a blazer 99 engine with the same characteristics.

After a day or two of using it, the "Service Engine Soon" light turned on and it diagnosed the Knock Sensor. So we switched the knock sensor from the other engine and placed it on the running one. Apparently that took care of the problem, until yesterday (one day after) that the light turned on again.

I don't know what to check for now, the truck is running fine but I don't want to risk it and have a bigger problem later.
Can someone please guide me into what I should look for doing?

Thanks

The code does not say the part is bad, it just tells you there is a problem in that circuit. Since you swapped engines, is it possible you pinched a wire? It also would help to know the exact code.

Thank you, I will have to disconnect the gas lines to check if there is any wire disconnected.

But one other thing, the check engine light turned off already.. Does this mean it might have worked?? It happened twice already but this time it hasn't turned on in 5 days or so

If the car has completed its drive cycle and found no errors the check engine light will turn off. It will still show as a history code on a scan tool. If it is now off and has no issues I would probably let it go unless it came back on again. That is up to you though. Actually, if it were me I would probably clear all codes and drive with the scan tool connected and monitor the knock sensor through the tool.