There are a number of different propane injection systems, but one thing they have in common: the propane is bled into the intake airstream. Unless it was changed, look for a bung that has been capped.
Here's the deal with propane: it's a relatively inexpensive way to add a bunch of power. With power comes risks. Used in moderation, propane can/will increase your rear wheel horsepower by 80hp. If you run it on the edge, you can tweak a little more than 100hp out of it. Too much propane going into the system too soon can damage the engine. It's safer to stay in the 80hp range. Using propane in moderation doesn't add wear and tear. It's the hard, abusive driving that would add wear and tear. I love my system, and would do it again in a second, if I needed to. Here's a word of caution, though. You're dealing with a highly flammable gas, in fairly large quantities, and it's under pressure. With propane, there are no little mistakes.