Ok guys, just to close this thread in case it is of use to anyone.

To recap, fuel trims way out of whack, calling lean to the Max. Therefore the injectors are putting more fuel in - you can smell it at the back of the car, tons of fuel coming out.

Lots suggesting a massive air leak, but to my mind, any air leak this size would be found by a simple inspection and a few squirts of some volatile fluid, which I'd already done. I know my hearing is not that great, but I could not hear a damn thing leaking, and no squirting was making any difference.

NO FAULT CODES - ALSO, just passed inspection.

Fuel consumption absolutely terrible.

O2 sensor readings screwy - both sitting around the zero mark with some small swings either way.

Fuel system reporting in closed loop and getting adjustments from the O2 sensors.

After much probing, heater circuits were fine on both O2 sensors, and readings, albeit small, were coming out the back of each sensor on my DVM with the engine running. Also checked this with frequency.

Graphing on the diagnostic app showed little to no response from the O2 sensors.

Wiring checked, everything plugged where it should have been.

I could not make sense of the O2 sensor readings, and checked the app and bluetooth adaptor on another car - all good there.

New O2 sensors ordered.

Absolute ba****rd to fit them. Just managed to do the right hand one in the car. Left hand one, the CAT had to come out as it was seized solid.

Both replaced - car running perfectly now, fuel trims are spot on (no air leaks!). 02 sensor readings and graphs are text book. Been for a drive and she runs like a dream. MPG also coming back quickly.

Thanks to everyone for their help on this...

On to the next job now.

 

Good job!