1, If you want it to be reliable don't use second hand parts.
2, Fitting LPG is NOT a DIY job. Strict regulations apply to the fitting of LPG systems and must be done by suitably qualified techs.
3, The cost of the system depends mainly on the quality and technology of the system being installed. If you have a carby petrol vehicle then you can get away with the cheaper "carby" type LPG systems but you still want quality components and fitting for reliabillty. If your car is EFI then it's worth paying a bit more for an LPG injection system. LPG injection gives much more precise fuel control, virtually eliminates the possibillity of backfiring and allows rev limiters and traction control (where fitted-not talking Patrols here) to operate normally.
There are now 2 types of LPG injection systems vapour injection and liquid injection. Vapour sequential injection will see only about a 5% drop in power when you switch from petrol to gas. The more expensive liquid sequential injection will actually increase power by 2 or 3% when running on gas. They do this by injecting liquid LPG into the intake port where it evaporates to a vapour causing an intercooling type effect, latant heat of evaporation I think it's called.
Patrols do cost a bit more to convert than most as in most cases it requires the fitting of a sub fuel tank for Petrol. Most people opt to put the LPG tank where the standard fuel tank was fitted hence the need for a new petrol tank.
I live in QLD and in my previous job was a qualified LPG fitter/repairer. I fitted Parnell vapour sequential injection systems to my '94 EFI Patrol (since sold the car) and my wifes BA Falcon wagon which we still have. We were able to claim the government rebate ($2000 per vehicle at the time) for both vehicles. Doing the labour myself meant both systems owed us very little after rebate.
Tony
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