Translation:I wanted to know if you had liked it.
Volevo sapere se gli ero piaciuto would be I wanted to know if he liked you. I'm not sure about the passive. I don't know if I've done that yet. Piacere does it opposite way around, means 'is pleasing to' http://italian.about.com/od/verbs/a/italian-verb-piacere.htm
"I wanted to know if you were liked" is incorrect because "ti" is the object of the liking. In other words something is pleasing to "ti" (you). I'd translate your sentence as "Volevo sapere si eri piaciuti" (literally "I wanted to know if you were pleasing to one," but don't depend on that.