ill give that a shot if this doesnt pan out. but now its been 3 items, o2 sensors, maf or could of been weak plugs. and my plugs had some serious color to them. for anyone interested

https://photos.app.goo.gl/bPoHcd1TueNjWSkg6

I’d definitely do the plugs they look old although doubt it’s causing this particular issue have you done the genuine maf yet? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

i did plugs. am waiting on delivery atm, eurocarparts only has delphi and not denso.

Don’t even bother with Delhi-

Message duckworth parts on here and you’ll get the forum discount on a denso maf it’s the only way to do it right. Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

This was the leak on my engine that caused it to run lean. Couldn't detect by the usual methods.

Same issue on mine at the pcv
Crap design, wrapped with self amalgamating tape to resolve

Would a smoke test not show the problem? Also doesnt explain why it only errors on 1 bank on LPG. Am getting GAP tool today, and maf on monday hopefully. So can also install new sensors and clear adaptive values.

Mine only had the code on LPG and on one bank. It was fine on petrol.
I think the answer is in the fueling map overlay for the LPG system. LPG has a lower calorific value than petrol, so you have to put more LPG in to get the same bang as petrol. LPG systems tend to run a little leaner than petrol (certainly on mine it does but normally the fuel trims are able to correct fueling to obtain a good mixture). But with the leak, on petrol, the fuel trims are able to accommodate the air leak influence. However, on LPG the trims don't have enough authority to pull the fueling back in, so you get a lean code.
Either way, mine ran fine on petrol, but was lean on 1 bank with LPG. I sprayed brake cleaner around and had no change in engine speed, so assumed no leak. Rebuilt my supercharger and replaced all inlet gaskets and the PCV pipe (£100+ !) etc at the same time, still lean on LPG only. Installed the 22mm rubber hose on the PCV system with a couple of jubilee clips and not a single problem since, on petrol or LPG.
The other option is that the fuel map on your LPG system is incorrect. However, if it worked fine before, its something else at fault as the software is deterministic (always does the same thing).
Hope this helps. Rob 05 L322 4.2SC
2016 Discovery 4 Graphite
Lotus Carlton
Ascona 400
Volvo V70R AWD manual
Suzuki 1200 Bandit
Velocette Venom
BMW R80/7
Daimler V8 250
Mini Cooper S Works 2006

ah so get this. on petrol both banks are lean, only lpg, only bank 1 is lean

And if it helps, the reason I know my LPG system fuels leaner is because I can watch the fuel trims increase when I change from petrol to LPG as they richen the mixture to achieve the correct fueling. The result is the fueling is OK, as long as the adjustment is within the authority the trims have.
Rob. 05 L322 4.2SC
2016 Discovery 4 Graphite
Lotus Carlton
Ascona 400
Volvo V70R AWD manual
Suzuki 1200 Bandit
Velocette Venom
BMW R80/7
Daimler V8 250
Mini Cooper S Works 2006

Did it run rough or idle rough or just throw the code? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

Just threw the code. It did onetime idle a bit rough, but i think thats due to deviation in fuel trims between petrol and lpg. so i cleared the errors, put 20quid of petrol in there and went for a hard drive. issues came back, so waiting on the maf and gap to turn up

mgrover wrote:

ah so get this. on petrol both banks are lean, only lpg, only bank 1 is lean

ill give it a shot when my other fixes dont pan out its a bit of an annoying issue since it only occurs in certain parts of the rev range but never when idling

Mine never happened on idle. Once I was driving, initially it only happened when I drove faster, if I drove very steady it was OK. However, once I fitted the expensive (did I mention that !) OE pipe, I think the leak got worse and it happened every time I drove it pretty much. 05 L322 4.2SC
2016 Discovery 4 Graphite
Lotus Carlton
Ascona 400
Volvo V70R AWD manual
Suzuki 1200 Bandit
Velocette Venom
BMW R80/7
Daimler V8 250
Mini Cooper S Works 2006