My grandpa left me his 2004 dedicated LPG BA Falcon to drive when he went overseas, but I was shocked at how much fuel it was consuming. According to the trip computer it was doing 24-25 L/100km, but I managed to get that down to 22 L/100km after a few days of 'nanny' driving, which is still outrageous. I don't know what the problem might be.
Based on your figures it's consuming about 50 percent more LPG than it should. It should be doing around 17-18 L/100 km on LPG, not 24-25. I would have the LPG system serviced, and the spark plugs and plug leads changed.
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