Not true, at my dealership, we run duel fuel engines (you can select which fule to use), run on either gasoline or propane. One of the engines we run in caterpillar forklifts are GM's 4.3L which is designed to run on propane. They also use ECM's with sensors just like our vehicles. But for the older stuff, it's mostly run by vacuum similar to a gas carburator setup, or venturi.bigdogg said:i dont think you can on the gas motor, fare as i know its only for dieasles