To follow up the guy who owns and uses a PicoScope a member of this forum is called Terry and I would guess based on Steve's location live in the Worcester area. With luck he'll post his view on this issue.
Today's post by Steve is as follows:
OK, this is not going to be easy to explain clearly.
I have already etsablished that when viewing real time 02 data
(voltage and STFT) the STFT does NOT represent an output from the
02's as you would assume. It is an aspration, a requirement or
expectation of the ECU, not an 02 reading at all. So, STFT info has
to be ruled out as evidence that the 02's are working.
I've run the engine up from 13C coolant temp this morninng and
watched the 02 info. They are both flatlined at 0.000V and +24.2%
When the 123 failure occurs around 80C coolant, an engine restart
will either see the engine run on 456 only, or sometimes on all 6,
it's a bit of a lottery. When running on all 6, I may see 02
voltages as I'd expect, 3.2V is one I rememeber seeing, and
voltages are shown for both B1 and B2 02's for a time.....along
with STFT's you'd expect.
Until cyls 456 drop out that is.
When 123 fail once more, both 02's flatline at 0.000V and the STFT
shoots up to 24.2%.
I'm beginning to think the 5V supply to both 02's is being cut
somehow. I doubt the 02 heater circuit is at fault as I'm revving
the engine to high exhaust temps, so the 02's are not going cold
due to the lack of their heaters.
In both cases, I'm going to have to check for the presence of both
the 5V 02 sensor supply, and the heater circuits, although the
latter I'm sure I did months ago.
Having seen proper, varying voltage outputs from both 02 sensors on
occasions, this probably provides proof that both 02's are good,
viable. It would be easy to think they are both useless when they
are aparently flatlining, but that is effect, not cause. Something
is causing both of the 02's to drop to 0.000V when they should be
bouncing up and down the voltage range. That might be the source of
all my trouble with this car.