I am an LPG expert...
Regarding 'How will I know if the LPG is running lean on my V70'....
I don't know what type of system is installed on the V70. On an older V70 the MIL light not come on as long as the lambda signal flicks occasionaly. On a newer V70 the MIL light is more likely to come on if the mixture is incorrect at any point in the load / rpm range, even if the lambda signal flicks occasionally.
If it is a modern sequential system on a newer V70 then the MIL light should come on if the engine runs lean, but only during the petrol system's 'closed loop mode' operation. Closed loop mode is the usual mode, but from a cold start, on the over-run or on high engine loads (when you put your foot down) the engine runs 'open loop mode' (i.e. it ignores the lambda signal). It is possible for a vehicle to have the correct mixture on LPG most of the time, but to run lean when the driver puts his foot down. If the engine runs lean when the driver puts his foot down, this will do more engine damage and sooner than if the engine runs lean at part throttle. The way to check is to monitor lambda signal under such conditions.
If it is an older system (single point or multipoint none sequential) then the lambda signal might be emulated to prevent MIL light illumination. In these cases the only way to know if the mixture is lean is to connect to the LPG system or connect to the lambda probe with a voltmeter. It is unlikely one of these systems is fitted to a later V70, as later V70's use a type of lambda probe that isn't compatible with the lambda input on older LPG systems... But I owned a V70 with a multipoint none sequential system where the installer had fitted a second lambda probe specifically for the LPG system!
The best way to check all is OK if you don't know the type of LPG system would be to visit a good LPG installer who knows all the systems...
Simon
www.Lpgc.co.uk