Gasoline only, won't work with diesel IIRC. I looked into it years ago when it first came out, as it's pretty neat stuff.
Also, your fuel system can "digest" a certain amount of air so long as it has the bypass present to the return line from the filter head. If you've plugged that off like a lot of people do chasing air intrusion issues, don't count on sending large amounts of air through the injection pump and having a positive result.