I have a x14xe engine in my nova, janspeed 4-2-1 manifold, custom exhaust, ind kit and mantzel powerbox and it is running very rich. The hydrocarbons and emmisons are both very high.
After a few checks it was found that if the lambda sensor was disconnected the ECU warning light didn't come on. The running also seems to be exactly the same with the lambda disconnected. Obviously with the lambda sensor disconnected from the car a fault should come up in the ECU's diagnostic system.
The wire between the sensor and ecu has been checked by ChrisB. We also plugged another lambda in, with it just sat on the engine and the running also seemed the same. With no faults coming up. According to the diagram I got with the ECU, the lambda wire needs to go to pin F9 on the ECU.
If any other sensor is unpluged the light comes straight on!