Changed both front O2 sensors for known good ones, cheers Rob
Light back on with 0420, 0430, 0300 and 0306
Will feed it on V Power over the weekend to see if that cures the first two, but stumped with the misfire
I've changed the loom for a good second hand one, fitted new coil packs, changed the fuel rail, fuel pressure regulator, injectors and loom, throttle body, MAF sensor, ECU and front O2 sensors. Plugs are GM quads and are changed every 20k. No oil or water in the plug wells either.
Runs well, and pulls like a train. But it has a tendency to run rough when started, both hot and cold, but not consistently. Turn it off and restart and it's fine, so still think that the problem is electrical rather than mechanical.
Definitely better since the loom change last week, and more so since the O2 sensors... still has a slight vibration at idle, but this engine has never idled that smoothly