Chevy 1500 Express Van 4.3L engine. I recently had my engine switched with a Jasper Replacement (290,000 plus miles). Continuing problems with Knock sensor code and catalytic converter code.
Is there a possibility that the stock ECM and Jasper Replacement don't like each other. What would be my remedy if this is the case?

 

I'd replace the knock sensor first.

 

why did you replace the engine
with the limited info you provided; what is the knock sensor code...do you have a audible engine knock...was the code there before

cat codes have nothing to do with the engine replacement. if the cat or 02 were bad before the engine replacement...they will still be bad after.