Have a 1993 200sx 1.8 turbo MOT failure in this morning. Has excessive CO at idle. Mechanically all seems well, Ignition seems good, Smoked the intake and fixed a small air leak, Eng temp sensor gives a reasonable output for a warm engine, new air filter needed and fitted.

I then checked O2 and MAF output's. Which were not nice.

First observation was the heater in the O2 sensor is not active (good supply and ground but no current flow) So an O2 sensor is needed, It is close coupled so I expected to see an amount of O2 switching with some cruise.

This is what I have got, Any opinions on this would be great.



Next was a good look around the exhaust manifold. Its a Zirconia 3 wire sensor so I was keen to check a decent earth path. There is a piece of earth strapping from the cylinder head to the manifold just after the turbo which has rotted off. Its pretty grotty and rotten in the area and I cant see a way of refitting without an extensive strip down and clean up (Which frankly the car is not worth) so would a good quality (Bosch/NTK) 4 wire Zirconia grounded back to the cylinder head be an acceptable fix????

Any opinions on the O2 sensor output would be great (I'm hoping someone has some as I'm not sure where to go now). The noise when its low worries me, Should it?? It seems to be rich at idle and then goes lean with any amount of throttle. I'm also very suspicious of the speed it switch's from rich - lean??? Seems almost instant?? Which I have never seen. Are these sensor problems that could be attributed to a poor earth or low temp?? or should I be believing the sensor and looking further at pulse width, fuel pressure etc.

Thanks.
Steve.