Being a Tickford gas system it has a self tune function, do a search as the proceedure for activating it is on here somewhere.
Apparently it should be done every 20k kms and after every time work engine work is done (like a Headgasket, leads, plugs etc)

My EL with factory Vialle gas system averages 12L/100km

On my EF I6 i get around 325 to 335 K's suburban driving while 450+ on freeway driving off a 69 ltr LPG tank. My LPG system is pretty new got it installed last year from Parnell,needs a retune atm.

Is it a SVI system or the old type donut system that parnell installed?

I'm gettting an avg of 17/100 from my lpg injection that parnell fit ( and could never get the tune right ) atm, but it needs the filters changed & an engine service again. I also swap cogs @ 3k rpm usually, which doesn't help the fuel consumption either. I tune it myself with my laptop when i change the filters & service the engine. After a service & filters, i usually get about 14.5/100 swapping cogs @ 3k rpm.

Cheers

ToranaGuy