Hey there, i have a 1990 GMC c1500 and i'm getting a code 43. Engine is running really rough, no power, and dies often, but will start back up right away. I have pretty much done a ton of research already on this but could not get all my questions answered. The issue seems to be that the knock sensor is not getting power,which led me to believe that the ESC was bad. I replaced it and still no power to the knock sensor. Just as a reminder the ESC has 4 wires going to it.

1st wire (red) is hot and I get 12 volts.
2nd wire is the ground and is grounded well
3rd wire is direct connection to knock sensor which i read should get about 5 volts and is getting none.
4th wire is the ECM signal wire (B7 on the ECM) and should get 8-10 volts (from what i read).

My question is: does wire 1 feed power to wire 3 and 4 (once it goes into and out the ESC). This seems like it would make the most sense to me, however after i replaced the esc and still no power i'm questioning that theory. So now i'm wondering if the ECM actually feeds power into the ESC and back down to the Knock sensor, which would mean i have a bad ECM. However if that is the case wouldn't i probably have a whole bunch of other problems being all the responsibility that the ECM has?

I guess that's it, hopefully i have explained it well enough. Oh, i have checked continuity on each end of all the wires, so my connections are good. Thanks for your help.