(ESC) Electronic Spark Control Module on 89 Chevy should be mounted near the throttle body of the TBI. May have letters HKR stamped on it.
I have a 92 s10 blazer and my code 43 was fixed by replacing the knock sensor. so maybe check the knock sensor and the wiring from that to the ECM.
1995 and eariler models use a separate ESC module mounted near the throttle body of TBI
knock sensor
thats your knock sensor ESC is Electronic Spark Control which governs timing.
The Arsenio Hall Show - 1989 1-43 was released on: USA: 2 March 1989
The Pat Sajak Show - 1989 1-43 was released on: USA: 8 March 1989
The firing order is 18 43 65 72.
replace the ignition module Its under the rotor inside the distributer cap
Code 43 is listed as Electronic Spark Control Circuit
any from 88 to 98
43