I am not an electrical engineer, but I tried your method with my '87 Supra and it failed, only solution was using a shielded wire and grounding one end. The KS system is finicky, it seems breaks in the connection(even when resoldered) or RF disruption of the signal from outside will cause it to throw a code, which causes the ecu to retard the timing to prevent engine damage.
Since you have already soldered in a new wire I would try the correct KS or Willards suggestion, then try to rewire it using the method used for the Supras.
http://oldschool.supracentral.com/htm/knock.htm
Is that using the oem wire?
Again, where is this one end being grounded. ECM to sensor, where is the wire grounded? Like splice to a ground?
