I’m not sure if the 1989/90 ECU will throw a code 42. From what I understand, it is possible for the engine to run with starter fluid, with the ECU completely disconnected, in these two years. IIRC, the ECU ‘monitors’ spark in these years, but doesn’t control it. That being said, the ECU should throw a code 41, if the ECU does not see the ignition signal. The first post here indicates that perhaps there is no longer a tach signal (tach needle not moving when cranking??). The tach signal is pulsing 12v to the ECU, and the ECU uses this signal to know when to pulse the injector.