Engine misfire once warmed up

[caransom]

Please can anyone help!  The engine runs smoothly until warm  then misfires after warm up since a new gearbox was fitted.  Have had sensors all tested, also spark plugs and HT leads sorted. Both sensors after cat show lean/low readings and will not switch rich even with throttle pumping. Also by this time engine is running rich so B1 S2 and B2 S2 data is incorrect. Maybe both lambda sensors are faulty but the fuel malfunction bank 1 error suggests a fault on only bank 1 whilst there is a problem with both banks, so there are 3 pieces of problem data which do not make sense. Latest outcome is that it is an ECU problem.  BUT, we had already had another ECU put in and tested, but this did not have any affect.
The car is a 2001 2.6 Omega.

[Entwood]

 ....mmmmm  gearbox changed .. so lots of work in the vicinity of the lambda sensors ...

damaged wiring to the sensors ??
wiring put on incorrectly (wired in reverse ??)
lambda heater wires not connected ??

As the problem only occurs once warm .. it reads like a lambda problem under closed loop conditions .... ok when cold under open loop

http://www.picoauto.com/applications/lambda-sensor.html

[caransom]

Thank you for that.
So I need to get the sensors tested on a "closed loop" ?
TY for replying to a very   FOO "Frustrated Omega Owner"  !!

[tigers_gonads]

As nige said, jack it up and swap the O2 sensor wires around 

I had a similar fault after I changed my engine.
Ended up burning 2 cats out so beware of sparks coming out of your tailpipe 

[caransom]

Thanks for the advice. Can anyone recommend a specialist Vauxhall mechanic who is a wizz at sorting this sort of problem out? We are in Berkshire.

[TheBoy]

B1S2 and B2S2 showing rich

What are B1S1 and B2S1 doing? Lean I guess, in which case wire up lamdas properly.

[caransom]

Can I just thank all of you who replied, esp Entwood (?).  When I mentioned problem had been with us ever since new gear box fitted and told him your suggestions, then it made sense - he checked wiring and sure enough it had been put back incorrectly !  A few other things needed sorting after so long sitting on the drive, but otherwise all is (so far) well and good.  Why couldn't the garage have checked the wiring in the first place??  And, would we have any come back on the company that fitted the gear box, as the problem arose from their installation ? 
ANyway, a very big thank you again as we really love our Omega!  (Just got to get it taxed and insured again now!)