O2 sensor removal

[Radar]

Any tips to remove the O2 sensor?

After 29 years mine has packed up. Is there a trick to removing it without taking that manifold and exhaust off?

[Brianmoooore]

Where's it hidden on your car? Readily accessible on the E30s I've seen with an O2 sensor.
If your car is 29 years old, it is first registered before 08/92 and is tested in the UK to emissions levels that are easily met without a cat. and its associated lambda (02) sensor.

[Radar]

Where's it hidden on your car? Readily accessible on the E30s I've seen with an O2 sensor.
If your car is 29 years old, it is first registered before 08/92 and is tested in the UK to emissions levels that are easily met without a cat. and its associated lambda (02) sensor.

It's located on the balancing pipe on the headers between the block, chassis leg and above the engine subframe. There's very little space to get any tools or heat on it. I think I'm resigned to dropping the headers. Even my friendly mechanic who has every tool known to mankind (and some others) can't get it to budge.

I need to replace it because something is clearly not quite right. What it's pumping out now is an MOT failure and it smells outrageously rich on start up. I think the CO levels need to be under 3.5% and mine's fluctuating between 6.5 and 8%.

[Brianmoooore]

3.5% CO and 1200ppm HC is the old requirement. Yours needs to be 0.2% or less and 200ppm or less. The former should be easily obtainable without a cat., and the latter no problem with a cat.
You say the car is very rich on start up? O2 sensor doesn't operate until it reaches operating temperature, so the fault may be elsewhere.
Anyone checked that the correct coolant temp. signal is reaching the ECU?
Is this an S14 engine? Unfortunately the E30 engine I'm least familiar with, but most UK versions were built without O2 sensors, so we know that the engine can run perfectly well without it, with the ECU running on a constant default value. Unfortunately, I don't know if this is provided automatically, like with the M20 ECU, or needs to be provided by an external pot., like the M40.

[Radar]

3.5% CO and 1200ppm HC is the old requirement. Yours needs to be 0.2% or less and 200ppm or less. The former should be easily obtainable without a cat., and the latter no problem with a cat.
You say the car is very rich on start up? O2 sensor doesn't operate until it reaches operating temperature, so the fault may be elsewhere.
Anyone checked that the correct coolant temp. signal is reaching the ECU?
Is this an S14 engine? Unfortunately the E30 engine I'm least familiar with, but most UK versions were built without O2 sensors, so we know that the engine can run perfectly well without it, with the ECU running on a constant default value. Unfortunately, I don't know if this is provided automatically, like with the M20 ECU, or needs to be provided by an external pot., like the M40.

German car, I bought it in Berlin. Removed cats last year when I fitted new exhaust. I’m friendly with my local testing centre so I can check it pretty much anytime I feel the need. They only test me to the earlier standard, so under 3.5% is fine... but I’m not passing now. Coolant sensor is not that old, though I am aware that they’re not really a time sensitive part and sitting unused (which my car does a lot of) is probably the worst thing for them.

In any case my 2.7 engine should be ready before I need another MOT and I’ll fit a new suite of sensors to that before the next MOT.

[Brianmoooore]

Since the UK MOT test became computerised, the discretion of the tester has been removed. The computer will say what the test limits are, so if the computer says 3.5%, then 3.5% it is. Just looked up the last production date for your model - June '91, so that explains it.
If the cat. has been removed, then there's no point in keeping the O2 sensor. It's job is to protect the cat., so if that's not there, then neither does the O2 sensor need to be.
There's only one version of the AFM listed for your car, so either the ECU will simply set a default value with the O2 sensor disconnected, or there's a pot. to set a simulated voltage (and trim the CO) built into it. I don't have a S14 AFM to check and see - is there an adjustment on the side of it (possibly under a red cap), and is it a mechanical air bypass screw or an electrical potentiometer?
Back to your original question - just disconnect the wiring from the O2 sensor, leave it in place and forget it.

P.S. The 3.5% - 0.2% confusion is because I'm getting confused between two current threads I'm replying to!