Car is a '96 Pajero on LPG. (I know! I don't need to be told again!)
3.5L DOHC model

It might be a long shot, but something's sitting in the back of my mind that
says my original thoughts may have been wrong.
The car used to drive fine on both petrol and gas. Then, when on petrol, it
would start to drive as if it wasn't getting enough fuel. This would happen
after driving about 120km or so. It would then do this every time I put my
foot down to overtake or take off with any grunt. Initial thoughts were that
the fuel pump was on it's way out, because it was a somewhat intermittent
problem, as the next day, the car would be fine again for about another
180km.
Eventually the problem deteriorated to the point where the car basically
runs on about 3-4 cylinders when it's on petrol. On gas it's fine. At this
point, we started to think it was either the fuel pump, and then, once the
fuel pump was tested to be OK, we thought perhaps badly blocked injectors.
Again, another pricey problem. I continued to drive the car solely on lpg.
It's been 6 months now with no dramas, and have decides to look into it
further. It's a pain in the a.s to have only a 300km maximum range.
Recently, I had the LPG system 'de-gunked' from the wax sh.t that builds up
and causes shitty running when cold. The guys had major difficulties getting
the mixtures right afterwards, and discovered that the lpg computer was
faulty, and would cost about $500 to replace. Funds were lacking, so they
just disconnected it, and set mixtures best as possible, and all was fine.
Now, I spoke to another mechanic about it, and he suggested that if the
oxygen sensor was gone, it could cause the engine to run very badly (ie: on
3 or 4 cylinders) because it's not telling the computer to inject enough
fuel. He said also that because the lpg computer got it's information from
the oxygen sensor, then it might 'appear' to be faulty because it's working
off dodgy information from the stuffed oxygen sensor, but in actual fact not
be faulty at all.
Does any of this make sense to anyone, or does it sound like sh.t?
Crash Lander