S14 SR20DET - o2 Sensor issue

[Steve13]

Hey guys,

I have a S13 running a S14 SR20det. Been chasing an issue for a while now. At part throttle (trying to maintain speed, any speed, any gear), It's a bit lumpy and running a bit strange, yet runs fine on full throttle and idle.

I've replaced the o2 sensor because when I unplugged it, it ran fine. However with new o2 sensor in, it does the same thing. But unplugged is fine.

I've been trying to find some info on how it earths etc, because when I have the key in the on position, i'm getting 12v at one of the wires. However I can't seem to pick up an earth on the other one. According to my continuity test both wires run back to the ecu. One goes to pin 115 and the other goes to pin 110 which is also Fuel Injector 2 Drive Input (according to wiring specialties pinout on their website). Anyone shed some light on where it gets it's earth from or if it sounds like a different issue altogether? Starting to think my ecu has failed.

Does have a wiringspecialties harness
Has a WC ECU in it

Any help would be appreciated

Thanks