Almost complete with a restoration of a 91 Talon. Shop is getting OBD1 code 0031, knock sensor circuit malfunction. The knock sensor was new, but swapped it out with another new one. Same code. Checked wiring to ECU, no issues there.

ECU was refurbished by ECMLink. They confirmed it was tested and shouldn't be giving a false reading.

The knock sensor isn't over tightened.

Any ideas? Thanks in advance.

Maybe phantom knock giving it off I had that happen before.

Is it a 1g knock sensor?

My bet is wiring. I know you said it's ok, but did you trace it all the way from sensor to ecu? I had the same issue and rewiring it solved it. It's a weird shielded wire that taps into the o2 circuit.
This guide might help you out:
http://clintsgarage.blogspot.com/2010/05/how-to-rewire-your-knock-sensor.html

Unless u unloomed the wires and checked it from the sensor to the ecu I wouldnt cross it off the list just yet.

I have rebuilt my engine and transmission for my 91 Talon have it installed and running great. Now I have this same issue. Never had this issue before. I'm going to rewire it see what happens.