O2 Sensor failed or somehing else?

[Emit]

This is a cross post from another place - I'll update this thread when I get some resolution, apologies...

My car has started to hunt after warm up over the last few months, so I decided to reset the CO adjustment, last time I set it a few months back it was happily fluctuating between 15 and 20 on the 8cyl scale. Today I connected the dwell meter and its sticking on 42.5, I can bring the adjustment either way until the engine cuts out, and no change in the reading, some background:


Disconnected O2 sensor brings it to 22
Holding the WOT switch brings it to 26
FV is buzzing
Engine was rebuilt by me, grounds are good
I can set the CO so the engine is happy, runs ok
O2 sensor isn't a bosch one, less than a year old


I would have thought an o2 failure would bring it to 22, i.e. disconnected, but maybe it's failed the other way? any and all input appreciated :)

[Bitsyncmaster]

I would replace the O2 sensor first. It's rare the lambda ECU would fail like that but guess it could happen.

[David T]

My guess is either the connection between the O2 sensor and the ECU (and the ground connection) is not good and/or you have vacuum leaks.

[Emit]

I would replace the O2 sensor first. It's rare the lambda ECU would fail like that but guess it could happen.

Correct, it was the o2 sensor :) Replaced it with the genuine bosch one and it came back to life. Night and day difference when I put them side-by-side, the bosch one is much more robust.

Dialed in my settings and its running smoothly. As an aside because it's not running rich its getting up to temp much faster.