[V8] Knock sensor#1

[george.fallot at verizon.net]

     I have been getting poor gas mileage lately and also the check engine
 light comes on when under a load, like going up a hill. I have a 1990 V8
 from California. 
    I pulled the codes and found code 2142-knock sensor #1. Does anyone
 know which of the two knock sensors this is? It looks easy to change,at least 
in the manual, but I would like to know that I am changing the correct one. Anyone
know if the part is easy to find? How much?BTDT?
        Thanks,George