I have a 93 jimmy 4.3 cpi. It runs really rough at an idle. Checked the codes on it and I get code 43, knock sensor cicuit. I started by checking the timing with a light and tapping on the block to check the knock sensor. Turns out when I checked the timing it was jumping around all over the place (+,-, 15 degrees). Kinda hard to see the timing moving when you hit the block if it is jumping around already. The timing chain is good (first thing that came to mind when I saw the timing jumping around like that) and the dist. doesn't have anything loose in it. Pulled the computer down thinking mabey it was a bad wire, that was part of the problem. So here is a list of what I have done since then. I replaced the dist. module and all the wires on the dist. (they were the bad ones), New knock sensors and wiring (just in case), new cap, rotor, plugs and wires. Still get the same knock sensor code and the timing (while slightly better now) still jumps around. I plugged it into my brothers snap-on scanner and when I tapped on the block we did get a knock signal. So as far as I can tell everything now points to a bad ESC. Problem is, the spark controll in the cpi trucks is part of the of the ECM. I want to know if that would be the next best thing to try, and if so what computers are compatible with it. There are lots of throttle body 4.3's at the boneyard but not many spider injected ones. This system seems to be quite a bit different but if the older ones have the prom chip, couldn't I just use any computer with my prom?

 

I have a 93 s10 blazer with the same cpi unit and it has 2 knock sensors one on passengerside behind the head and the other is on drivers side by the exhaust hope you checked both wires the other thing you can do is to check the intake for leaks useing some carbcleaner.and did you unhook the wire on the passenger side behind the carpet before you set the timing ?when done you need to clear the computer and test I know the timing on mine is 0%btc I have it at 6% and runs fine and it gave me 3-4 miles better mileage.good luck on this...j

 

Yea, both knock sensors are new along with the plugs on them and the wire to the computer (the one on the back of the head was a pain in the ***). Yes, I know about the plug for the timing and I set mine at 6 degrees also, same results. Oddly enough a vaccum leak never came to mind. I will have to check that out. Oh and yes I cleared the codes. It comes up right away even when it is cold and the computer is not relying on the knock sensors, that's what is making me think it might be the esc. Thanks for the advice!!