My 91 silverado odbI code 43 any ideas

Hello All,
I have a 91 Silverado 305 2WD. In march 2K5 I did tune up.. plugs,rotor,cap,wires, air filter. All ran fine until September same yr. Engine stalling stumbling, found out it was fuel filter, changed it ran like a bat out of hell until November, Check Engine light came on. I use a piece of wire to jump the ODBI diags, and get a code 43. Book says it' knock sensor, wire from K.S. to Elertronic Spark Control module, or ESC module itself.
Any diags i can perform, or do i have to go to a dealer?
$ to tight to mention.... ;-)

Thanks for any thoughts